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Multiple chemical sensitivity

2024-11-24T20:21:00Z

Aletheia2020:spelling

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal | last = Rossi | first = Sabrina | authorlink = | last2 = Pitidis | first2 = Alessio | authorlink2 = | date = Feb 2018 | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{Cite book | url =|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|chapter-url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS | first = |location=Università degli Studi di Milano, Italy | date = 2019-05-23|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and [[mold]].<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="1.2-trigger">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
==Signs and symptoms ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal| year = 1999 | title = Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /> that symptoms range from mild to severely disabling,<ref name="Ch1" /><ref name="NICNAS" /><ref name="TaskForce2017">{{Citation | last = Task Force on Environmental Health | date = 2017 | url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf | title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal | last = Steinemann | first = Anne | authorlink = | date = Mar 2018 | title = National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name="TaskForce2017" /><ref name="Loria2017">{{Cite journal | last = Loria-Kohen | first = Viviana | last2 = Marcos-Pasero | first2 = Helena | last3 = de la Iglesia | first3 = Rocío | last4 = Aguilar-Aguilar | first4 = Elena | last5 = Espinosa-Salinas | first5 = Isabel | last6 = Herranz | first6 = Jesús | last7 = Ramírez de Molina | first7 = Ana | last8 = Reglero | first8 = Guillermo | date = 2017-08-22 | title = Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref name="Gibson2016-unmet">{{Cite journal | last = Gibson | first = Pamela Reed | last2 = Leaf | first2 = Britney | last3 = Komisarcik | first3 = Victoria | date = 2016-01-12 | title = Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5 | pages = 75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref name="García2014">{{Cite journal | last = García-Sierra | first = Rosa | last2 = Álvarez-Moleiro | first2 = María | date = 2014-07-01 | title = Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2 | pages = 95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref name="Alobid2014">{{Cite journal | last = Alobid | first = Isam | last2 = Nogué | first2 = Santiago | last3 = Izquierdo-Dominguez | first3 = Adriana | last4 = Centellas | first4 = Silvia | last5 = Bernal-Sprekelsen | first5 = Manuel | last6 = Mullol | first6 = Joaquim | date = 2014-12-01 | title = Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal | last = Gibson | first = PR | author-link = | last2 = Vogel | first2 = VM | authorlink2 = | date = Jan 2009 | title = Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1 | pages = 72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Koch2006">{{Cite journal | last = Koch | first = Lynn | last2 = Vierstra | first2 = Courtney | last3 = Penix | first3 = Ken | date = 2006-09-01 | title = A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS can include [[headache]], [[migraine]], [[cognitive dysfunction|neurocognitive deficits]], [[dizziness]], [[fatigue]], [[arrhythmia|cardiac arrhythmia]], [[tachycardia]], [[hypotension]], [[hypertension]] (high blood pressure), [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], [[myalgia|muscle]] and [[Arthralgia|joint pain]], [[skin rash]]es, [[hives]], [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name="NICNAS" /><ref name="Valderrama2015" /><ref name="TaskForce2017" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal | last1 = Genuis | first1 = SJ | date = May 2013 | title = Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5 | pages = 572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291 | last2 = Ross | first2 = PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation. | last3 = Whysner | first3 = J | last4 = Covello | first4 = VT | last5 = Kuschner | first5 = M | last6 = Rifkind | first6 = AB | last7 = Sedler | first7 = MJ | last8 = Trichopoulos | first8 = D|via=}}</ref><ref name="Ross1999-Olfaction">{{cite journal|vauthors=Ross PM, Whysner J, Covello VT, Kuschner M, Rifkind AB, Sedler MJ, Trichopoulos D, Williams GM| year = 1999 | title = Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5 | pages = 467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN| year = 1999 | title = A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2 | pages = 73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book |isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp | title = A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs | date = 2010 | last=National Industrial Chemicals Notification and Assessment Scheme | last2 = Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathologies."<ref name="Rossi2018" /> It can be associated with very high levels of disability. [[File:Cosmeticsbottles.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">{{Cite book | title = The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link= | url = |access-date= | date = 2017 | publisher=The text publishing company | last = Grenville | first = Kate | authorlink = |others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne, Australia | editor-last = | editor-first = |editor1-link=|editor-last2 = |editor-first2 = }}</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation |url = https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf | title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety | date = 2009|location=United States | page = 9}}</ref>]]
=== Chemicals that trigger symptoms ===
The following substances are common triggers for adverse symptoms in people with MCS:
* [[pesticide]]s (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic [[fragrance]]s and products containing fragrance (e.g. fragranced deodorant)
* laundry [[detergent]]s and fabric softeners
* [[cigarette smoke]] and woodfire smoke
* [[petrochemical|petrochemical solvents]] and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (e.g. [[tartrazine]])
* some [[medication intolerance|medications]] and anesthetics
* [[air pollution]] (e.g. [[black carbon]], [[nitrogen oxide]], [[ozone]])
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name="NICNAS" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15">{{Cite book | title = [[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]] | last = Pall | first = Martin L. | authorlink = Martin Pall|publisher=Routledge & Harrington Park Press | date = 2007 | isbn=978-0789023896|location=New York}}</ref><ref name="Valderrama2015">{{Cite book | last = Valderrama Rodríguez | first = M | last2 = Revilla López | first2 = MC | last3 = Blas Diez | first3 = MP | last4 = Vázquez Fernández del Pozo | first4 = S | last5 = Martín Sánchez | first5 = Jl | title = Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS) | date = 2015 | trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name="Ziem2018">{{Cite journal | last = Ziem | first = Grace E. | authorlink = | date = 2018-04-24 | title = Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Pigatto2019" />

==Diagnosis and diagnostic criteria ==
Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name="NICNAS" /><ref name="TaskForce2017" />

===International Consensus Criteria 1999===
The 1999 international consensus on MCS is the most commonly used diagnostic criteria for MCS. The consensus is based on the Cullen criteria plus a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /><ref name="pmid10444033" /> MCS is defined as:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book | title = Psychiatry: An evidence-based text | pages = 793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date= | date = 2009-11-27|publisher=CRC Press | last = Hooper | first = Malcolm | authorlink = Malcolm Hooper|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location= | editor-last = Puri | editor-first = Bassant|editor1-link=|editor-last2 = Treasaden|editor-first2 = Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
===Lacour criteria 2005===
# symptom duration of at least 6 months
# symptoms in response to at least 2 of 11 categories of chemical exposures
# at least one [[central nervous system]] symptom is present (eg [[fatigue]], [[headache]]s or [[cognitive dysfunction|neurocognitive deficits]], and one symptom from another organ system
# symptoms causing adjustments of personal lifestyle, or of social or occupational life
# symptoms occurring when exposed and improving or resolving when exposures are removed
# symptoms are triggered by exposure levels that do not induce symptoms in other individuals who are exposed to the same levels<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref><ref name="Tran2013">{{Cite journal | last = Tran | first = Marie Thi Dao | first2 = Lars | last2 = Arendt-Nielsen | first3 = Ron | last3 = Kupers | first4 = Jesper | last4 = Elberling | title = Multiple chemical sensitivity: On the scent of central sensitization|journal=International journal of hygiene and environmental health|volume=216|issue=2|pages=202-210 | date = April 2013|pmid=22487274|url=http://www.bcwomens.ca/Specialized-Services-Site/Documents/Complex%20Chronic%20Diseases%20(CCDP)/Multiple%20Chemical%20Sensitivity%20(journal%20article).pdf | doi=10.1016/j.ijheh.2012.02.010|pmc=|quote=|access-date=|via=}}</ref><ref name="Damiami2021" />
===Diagnostic tools===
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />
===Differential diagnosis ===
A series of tests are needed to identify other potential causes of the symptoms. Particularly important to rule out are:
*[[Porphyria]]s
*[[Mastocytosis]] including systematic mastocytosis<ref name="Damiami2021">{{Cite journal | title = Italian Expert Consensus on Clinical and Therapeutic Management of Multiple Chemical Sensitivity (MCS) | date = 2021-10-27|url=https://doi.org/10.3390/ijerph182111294|journal=International Journal of Environmental Research and Public Health|volume=18|issue=21|pages=11294 | last = Damiani | first = Giovanni | last2 = Alessandrini | first2 = Marco | last3 = Caccamo | first3 = Daniela | last4 = Cormano | first4 = Andrea | last5 = Guzzi | first5 = Gianpaolo | last6 = Mazzatenta | first6 = Andrea | last7 = Micarelli | first7 = Alessandro | last8 = Migliore | first8 = Alberto | last9 = Piroli | first9 = Alba | last10 = Bianca | first10 = Margherita | last11 = Tapparo | first11 = Ottaviano|doi=10.3390/ijerph182111294|pmc=PMC8582949|pmid=34769816|issn=1660-4601}}</ref>

==Prevalence==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" />]] While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="NICNAS" /> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="TaskForce2017" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC | date = May 2004 | title = Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5 | pages = 746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Bloch2007">{{Cite journal | last = Bloch | first = Richard M. | last2 = Meggs | first2 = William J. | date = 2007-01-01 | title = Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression | url =https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref name="Berg2008">{{Cite journal | last = Berg | first = Nikolaj Drimer | last2 = Linneberg | first2 = Allan | last3 = Dirksen | first3 = Asger | last4 = Elberling | first4 = Jesper | date = 2008-07-01 | title = Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population | url =https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7 | pages = 881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref name="Andersson2008">{{Cite journal | last = Andersson | first = Linus | last2 = Johansson | first2 = Åke | last3 = Millqvist | first3 = Eva | last4 = Nordin | first4 = Steven | last5 = Bende | first5 = Mats | date = 2008-10-01 | title = Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5 | pages = 690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}<ref name="Gibson2016-MH">{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM | date = Apr 6, 2016 | title = Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf | journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Rossi2018" />

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305 | last = Steinemann | first = AC | title = A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health | date = 2005|volume=59|issue=6|pages=300-5}}</ref><ref name="Caress2009">{{Cite journal | last = Caress | first = SM | last2 = Steinemann | first2 = AC | date = 2009-02-01 | title = Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1 | pages = 71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Steinemann2018" />

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/ | title = Danimarca: nuovo codice per la MCS | last = | first = | authorlink = | date = 2014-10-14 | website = Infoamica|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14|url-status=}}</ref><ref name="Elberling2014-code">{{Cite journal | title = Patienter med symptomer, der er relateret til dufte og kemiske stoffer, kan nu kodes specifikt med Sundhedsvæsenets Klassifikationssystem | date = 2014-05-26|url=https://pubmed.ncbi.nlm.nih.gov/25096843/|journal=Ugeskrift for Laeger|volume=176|issue=11|pages=V10120627 | last = Elberling | first = Jesper | authorlink = | last2 = Bonde | first2 = Jens Peter Ellekilde | authorlink2 = | last3 = Vesterhauge | first3 = Søren | authorlink3 = | last4 = Bang | first4 = Søren | authorlink4 = | last5 = Linneberg | first5 = Allan | authorlink5 = | last6 = Zachariae | first6 = Claus | authorlink6 = | last7 = Johansen | first7 = Jeanne Duus | last8 = Blands | first8 = Jette | last9 = Skovbjerg | first9 = Sine|language=da|doi=|pmc=|pmid=25096843|access-date=|trans-title=A new classification code is available in the Danish health-care classification system for patients with symptoms related to chemicals and scents|issn=1603-6824|quote=|via=}}</ref>

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name="TaskForce2017" />{{Rp|37}}<ref name="CCHS2014">Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

While a 2018 study at the University of Melbourne found that 1 million Australians (6.5% of adults) reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name="Pigatto2019">{{Cite journal | last = Pigatto | first = Paolo D. | last2 = Guzzi | first2 = Gianpaolo | date = 2019-06-01 | title = Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name="Steinemann2018-Aus">{{Cite journal |url=https://www.sciencedirect.com/science/article/pii/S2211335518300457 | last = Steinemann | first = A. | title=Prevalence and effects of multiple chemical sensitivities in Australia|journal=Prev Med Rep | date = 2018 | volume=10|pages=191-4|issue=|doi=10.1016/j.pmedr.2018.03.007|pmc=PMC5984225|pmid=29868366|quote=|access-date=|via=}}</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name="Steinemann2018" /><ref name="Steinemann2018-Aus" />
== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name="Schwenk2004" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name="Schwenk2004" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref name="ICD10-GM">{{Cite book | title = ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&dq=%C3%9Cberempfindlichkeit%20T78.4&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4&f=false|access-date=| date = 2011 |publisher=Deutscher Ärzteverlag | last = World Health Organization | first = | authorlink = World Health Organization | last2 = DIMDI | first2 = | authorlink2 = |veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name="Ch4.1-Noharm" /><ref name="NICNAS" /> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" /> In 2012, Denmark introduced code '''DR688A1''' for ''Symptoms related to chemicals and scents'' (Symptomer relateret til dufte og kemiske stoffer fra SKS), in the [[Medically unexplained physical symptoms|Medically Unexplained Symptoms]], under ''R68.8 Other specified general symptoms and signs''.<ref name="Elberling2014-code" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html | title = Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) | last = Centers for Disease Control | first = | authorlink = Centers for Disease Control and Prevention | date = 2019-11-19 | website = [[Centers for Disease Control and Prevention]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

==Treatment==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name="TaskForce2017" /><ref name="Ch4.1-Noharm">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name="NICNAS" /><ref name="TaskForce2017" /><ref name="Valderrama2015" /><ref name="Ziem2018" /><ref name="Ch4.1-Noharm" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name="NICNAS" /><ref name="Gibson2003">{{cite journal | last = Gibson | first = PR | last2 = Elms | first2 = AN | last3 =Ruding | first3 = LA | date = 2003 | title = Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name="Ch4.1-Noharm" />

There is evidence that some patients with MCS might have [[hypoxia|poor tissue oxygenation]] when exposed to triggers,<ref name="Ch4.5">{{Cite book |chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> perhaps because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal | last = Horvath | first = I. | last2 = Loukides | first2 = S. | last3 = Wodehouse | first3 = T. | last4 = Kharitonov | first4 = S.A. | last5 = Cole | first5 = P.J. | last6 = Barnes | first6 = P.J. | date = 1998-10-01 | title = Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10 | pages = 867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref name="Ewing1993">{{Cite journal | last = Ewing | first = James F. | last2 = Maines | first2 = Mahin D. | date = 1993 | title = Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain | url =https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref name="Gregersen">{{Cite journal | last = Gregersen | first = Per | last2 = Klausen | first2 = Hans | last3 = Elsnab | first3 = Charlotte Uldal | date = 1987 | title = Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up | url =https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures helps some people.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book |trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were:
* face masks (with HEPA and VOC filters)
* portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters), and
* water purifiers.<ref name="Ch4.2" />

== Accessibility needs==
People with MCS typically experience significant access barriers to society and accessing services. They are also commonly subject to stigma and lack of understanding, perhaps because the condition is poorly understood. Nevertheless, it is recognised as a disability. For example, "a growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR" />

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name="TaskForce2017" /><ref name="Grenvillebook" /><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/ | title = Guidelines on the Use of Perfumes and Scented Products | last = | first = | authorlink = | date = | website = University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Steinemann2018-Aus" /><ref name="Flegel2015">{{Cite journal | last = Flegel | first = Ken | last2 = Martin | first2 = James G. | date = 2015-11-03 | title = Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name="stJosephs" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref name="notsosexy">{{Cite web |at=Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern | url =https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf | title=Not so sexy. The health risks of secret ingredients in fragrance | last = The campaign for safe cosmetics|publisher=The Environmental Working Group | date = 2010}}</ref><ref name="Steinemann2019-asthma">{{Cite journal | last = Steinemann | first = Anne | last2 = Goodman | first2 = Nigel | date = 2019-06-01 | title = Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6 | pages = 643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref name="Steinemann2019-international">{{Cite journal | title = International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products | date = 2019-05-01|url=https://doi.org/10.1007/s11869-019-00672-1|journal=Air Quality, Atmosphere & Health|volume=12|issue=5 | pages = 519–527 | last = Steinemann | first = Anne|language=en|doi=10.1007/s11869-019-00672-1|issn=1873-9326}}</ref><ref name="Nazaroff2004">[https://www.sciencedirect.com/science/article/abs/pii/S1352231004002171 Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865]</ref><ref name="Kumar1995">[https://pubmed.ncbi.nlm.nih.gov/7583865 Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433]</ref><ref name="Elberling2004">[https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2133.2004.06251.x?sid=nlm%3Apubmed Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203.]</ref><ref name="Elberling2009">[https://www.sciencedirect.com/science/article/abs/pii/S1438463909000728?via%3Dihub Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.]</ref><ref name="Mendell2007">[https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2007.00478.x Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.]</ref><ref name="Schnuch2010">[https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2009.09510.x Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.]</ref><ref name="Neuenschwander2010">[https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.200900228 Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.]</ref><ref name="Nielsen2010">[https://pubmed.ncbi.nlm.nih.gov/15910405/ Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.]</ref><ref name="Nielsen2002">[https://pubmed.ncbi.nlm.nih.gov/12122569/ Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.]</ref><ref name="Venkatachari2008">[https://pubmed.ncbi.nlm.nih.gov/18688467/ Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.]</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is anecdotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref name="mcs-cv19-quebec">{{Cite web | last = The Environmental Health Association of Quebec | date = 2020 | url=https://aseq-ehaq.ca/en/projects/mcs-covid-19/ | title = Impacts of Covid-19 Health measures on people with multiple chemical sensitivities}}</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common in Canada and Sweden.<ref name="Steinemann2018-Aus" /><ref name="Grenvillebook" /><ref name="TaskForce2017" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name="stJosephs">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref name="ch5">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS | title = [The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23 | first = | authorlink = |volume=|pages=|edition=|isbn=}}</ref><ref name="Mercy1999">{{Cite web|url=http://www.lassentech.com/eimcspro.html | title = Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol | date = Sep 1999|publisher=Mercy Medical Centers New York and California}}</ref><ref name="Fisher2008">[https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.]</ref><ref name="Rea-surgerych">{{Cite book | last = Rea | first = William J. | authorlink = William Rea | date = 1996 | chapter=41 Surgery in the chemically sensitive|volume=IV | title = Chemical Sensitivity Tools of Diagnosis and Methods of Treatment|chapter-url=https://books.google.co.uk/books?id=cbsL8cUnO_EC&lpg=PA2015&pg=PA2803#v=onepage&q&f=true|url=https://books.google.com/books/about/Chemical_Sensitivity.html?id=cbsL8cUnO_EC | editor-last = Environmental Health Center|location=Dallas, Texas|publisher=CRC Press|pages=2803-2850|isbn=0873719654}}</ref><ref name="VictorianHosp">{{citation |url = https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals | title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals | date = Aug 25, 2011|website =Victoria Department of Health}}</ref><ref name="canberra2018">{{Cite web|url = http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx | title = Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities | date = 2018 | last = ACT Department of Health|access-date= | website = | first = Canberra, Australia | authorlink=|archive-url=|archive-date=}}</ref><ref name="NSW-factsheet">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx | title = Fact sheet: Multiple Chemical Sensitivity Disorder | last = NSW Health | first = | authorlink = | date = Sep 2, 2015 | website = NSW Health|archive-url=|archive-date=|access-date=2020-05-14}}</ref><ref name="Hosp2017">{{Cite web | last = Australian Commission on Safety and Quality in Health Care | date = 2017 | url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf | title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name="SA2016">{{Cite web|url = https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf | title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline | date = Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name="WA2019">{{Cite web |url=http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf | title=Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline | date = Sep 14, 2010|publisher=Western Australia Country Health Service.}}</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name="canberra2018" /><ref name="VictorianHosp" /><ref name="WA2019" /><ref name="SA2016" /> As well, some individual hospitals have their own policies for MCS patients.<ref name="Mercy1999" /><ref name="QHC2010">[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== Housing ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref name="amputated-lives">{{Cite book |chapter=The Elusive Search for a Place to Live | title = Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st|volume=|language=|title-link=|chapter-url=http://www.chemicalsensitivityfoundation.org/pdf/amputated-lives-ch2.pdf | url=|access-date= | date = November 20, 2008|publisher=Cumberland Press | last = Johnson | first =Alison | authorlink = |others=|doi=|oclc=|quote=|location=Parramatta, Australia}}</ref><ref name="Homelessness2002" /><ref name="ANRESS-2020">{{citation | title=Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy | date = Sep 2020 | first = Sharyn | last = Martin|pages=2}}</ref><ref name="Gibson2016" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name="ActionPlan2018">{{Cite web |url = https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf | title=An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)|publisher=Final Report of the Task Force on Environmental Health|location=Ottawa, Canada | date = Dec 2018}}</ref>{{Rp|12}}

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name="Homelessness2002">{{Citation | last = Environmental Health Coalition | first = | authorlink = | date = March 11, 2002 | title = Homelessness at critical level for Western Massachusetts chemically injured|publisher=Western Massachusetts|pages=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name="ANRESS-2020" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name="Gibson2016">{{Cite journal | last = Gibson | first = Pamela | authorlink =
| date = 2016-01-01 | title = A Review of the Life Impacts of Environmental Sensitivities | url = |journal=Internal Medicine Review|volume=|issue=May | page = 9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* [[mold illness|mold]]
* carpet
* fumes from paint
* [[pesticide]] residue
* fumes from [nearby] laundry facilities
* fumes from cleaning products in common areas and
* [[cigarette smoke]].<ref name=":3" />
People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name="ActionPlan2018" /> The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.<ref name="ActionPlan2018" /> It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.”<ref name="ActionPlan2018" />{{Rp|7,12,19}}

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name="NICNAS" /><ref name="Schwenk2004">{{Cite journal | last = Schwenk | first = Michael | date = 2004 | title = Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name="NICNAS" /><ref name="Schwenk2004" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name="Schwenk2004" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

==Possible causes==
[[File:MCS-IEI-biomarker-VOCs.png|thumb|'''MCS patients versus controls: VOCs in breath'''<br>
Basal exhaled VOCs data for MCS and controls, acquired with the ORT-VOC, are shown in a density plot.<br>
Source: Mazzatenta et al. (2021). [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 Physiological Reports, 9, e15034].<ref name="Mazzatenta2021" />]]
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name="TaskForce2017" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name="TaskForce2017" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus for the cause of MCS is that it likely has multiple causes: biochemical, neuro-physiological, causes related to the limbic system and perhaps also genetic predisposition.<ref name="ch1.4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018">{{citation | url =https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 | title = Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport | date = Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or divide.

In 2021, a small study by Mazzatenta and colleagues found breath analysis of key [[volatile organic compound]]s (VOCs) differed between MCS patients and healthy controls, raising the possibility that breath analysis may be able to diagnose MCS in future. Breath analysis can already be used to aid diagnosis for some illnesses.<ref name="Mazzatenta2021" />

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

The [[Toxicant-induced loss of tolerance (TILT)|Toxicant-Induced Loss of Tolerance]] (TILT) hypothesis proposed by Miller (1996) uses the name TILT for multiple chemical sensitivity, and describes a two-phase process. First, there is ''either'' a single major exposure to chemicals ''or'' many smaller exposures, which then result in chemical intolerance or ''sensitization''. In the second phase, low or very low levels of exposure to chemicals cause symptoms that did not occur before sensitization.<ref name="Horowitz2014" /> According to the TILT hypothesis, [[Food intolerance|food and medication intolerances]] frequently occur along with chemical sensitivity. Miller (2021) believes that [[Mast cell activation syndrome|Mast Cell Activation Syndrome]] may account for TILT/MCS.<ref name="Miller2021" />

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name="1.2-trigger" /><ref name="NICNAS" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name="ch1.4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15" /><ref name="Pall2011">{{Cite journal | last = Pall | first = Martin L. | authorlink = Martin Pall | last2 = Satterlee | first2 = JD | date = 2001 | title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder |url = https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of [[limbic kindling]], neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="NICNAS" />

A 2019 scientific review said that while further research was required to confirm Pall's theory, his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name="ch1.4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name="Bell1999">{{Cite journal | last = Bell | first = Iris R. | last2 = Baldwin | first2 = Carol M. | last3 = Fernandez | first3 = Mercedes | last4 = Schwartz | first4 = Gary E.R. | date = 1999-04-01 | title = Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name="Bell-kindling">{{Cite journal | last = Bell | first = IR | author-link = | last2 = Rossi | first2 = J | authorlink2 = | last3 = Gilbert | first3 = ME | authorlink3 = | last4 = Kobal | first4 = G | authorlink4 = | last5 = Morrow | first5 = LA | authorlink5 = | last6 = Newlin | first6 = DB | authorlink6 = | last7 = Sorg | first7 = BA | last8 = Wood | first8 = RW | date = 1997-03-01 | title = Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs' theory of neurogenic inflammation.<ref name="Meggs2017">{{Cite journal | last = Meggs | first = William J. | date = 2017-05-09 | title = The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2 | pages = 83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name="ch1.4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref name="Reid2001">{{cite journal | title = Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6 | pages = 604–9|doi=10.1093/aje/153.6.604|pmid=11257069 | last = Reid | first = S | last2 = Hotopf | first2 = M | authorlink2 = Matthew Hotopf | last3 = Hull | first3 = L | last4 = Ismail | first4 = K | last5 = Unwin | first5 = C | last6 = Wessely | first6 = S | authorlink6 = Simon Wessely | date = 2001 | pmc=|quote=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref name="Gronseth2005">{{Cite journal | title = Gulf war syndrome: a toxic exposure? A systematic review | date = 2005-05-01|url=https://doi.org/10.1016/j.ncl.2004.12.011|journal=Neurologic clinics|volume=23|issue=2 | pages = 523–540 | last = Gronseth | first = Gary S|doi=10.1016/j.ncl.2004.12.011|pmid=15757795|issn=1557-9875}}</ref><ref name="VA2014">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf | title=Clinical practice guideline for the management of chronic multisystem illness | last = U.S. Department of Veterans Affairs, Department of Defense | date = Oct 2014}}</ref><ref name="Spelman2012">{{Cite journal | last = Spelman | first = Juliette F. | last2 = Hunt | first2 = Stephen C. | last3 = Seal | first3 = Karen H. | last4 = Burgo-Black | first4 = A. Lucile | date = 2012-09-01 | title = Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name="VA2014" />

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal | last = Rea | first = William J. | date = 2018-06-01 | title = A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin | url =http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6 | pages = 889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref name="Lieberman2006">{{Cite journal | last = Lieberman | first = Allan | last2 = Rea | first2 = William | last3 = Curtis | first3 = Luke | date = 2006-09-01 | title = Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3 | pages = 763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref name="Vojdani2003">{{Cite journal | last = Vojdani | first = Aristo | last2 = Thrasher | first2 = Jack D. | last3 = Madison | first3 = Roberta A. | last4 = Gray | first4 = Michael R. | last5 = Heuser | first5 = Gunnar | last6 = Campbell | first6 = Andrew W. | date = 2003-07-01 | title = Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7 | pages = 421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref name="WHO-Indoor2011">{{Cite book | last = Hänninen | first = Otto O. | authorlink = | date = 2001 | editor-last = Adan | editor-first = Olaf C. G. |editor2-last=Samson| editor2-first = Robert A. | title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal | last = Knibbs | first = Luke D. | authorlink = | last2 = Woldeyohannes | first2 = Solomon | authorlink2 = | last3 = Marks | first3 = Guy B. | authorlink3 = | last4 = Cowie | first4 = Christine T. | authorlink4 = | date = 2018 | title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref name="Quansah2012">{{Cite journal | last = Quansah | first = Reginald | last2 = Jaakkola | first2 = Maritta S. | last3 = Hugg | first3 = Timo T. | last4 = Heikkinen | first4 = Sirpa A M. | last5 = Jaakkola | first5 = Jouni J.K. | date = 2012-11-07 | title = Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref name="Mendell2011">{{Cite journal | last = Mendell | first = Mark J | author-link = | last2 = Mirer | first2 = Anna G | authorlink2 = | last3 = Cheung | first3 = Kerry | authorlink3 = | last4 = Tong | first4 = My | authorlink4 = | last5 = Douwes | first5 = Jeroen | authorlink5 = | date = 2011-06-01 | title = Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6 | pages = 748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "[[dizziness]], [[seizure]]s, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name="Bell1999" /><ref name="Bell-kindling" /><ref name="Meggs2017" /><ref name="Tran2013" />

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name="Meggs2017" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name="ch1.4" /><ref name="Bell1994">{{Cite journal | title = EEG responses to low-level chemicals in normals and cacosmics | date = 1994-07-01|url=https://europepmc.org/article/med/7778120|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 633–643 | last = Schwartz | first = G E | last2 = Bell | first2 = I R | last3 = Dikman | first3 = Z V | last4 = Fernandez | first4 = M | last5 = Kline | first5 = JP | last6 = Peterson | first6 = JM | last7 = Wright | first7 = KP | pmid=7778120|issn=1477-0393}}</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref name="Bell1998">{{Cite journal | title = Differential Resting Quantitative Electroencephalographic Alpha Patterns in Women with Environmental Chemical Intolerance, Depressives, and Normals | date = 1998-03-01|url=https://www.sciencedirect.com/science/article/pii/S000632239700245X|journal=Biological Psychiatry|volume=43|issue=5|pages=376–388 | last = Bell | first = Iris R | last2 = Schwartz | first2 = Gary E | last3 = Hardin | first3 = Elizabeth E | last4 = Baldwin | first4 = Carol M | last5 = Kline | first5 = John P|language=en|doi=10.1016/S0006-3223(97)00245-X|issn=0006-3223}}</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name="ch1.4" /><ref name="Callender1994">{{Cite journal | title = Evaluation of chronic neurological sequelae after acute pesticide exposure using spect brain scans | date = 1994-03-01|url=https://doi.org/10.1080/15287399409531843|journal=Journal of Toxicology and Environmental Health|volume=41|issue=3|pages=275–284 | last = Callender | first = Thomas James | last2 = Morrow | first2 = Lisa | last3 = Subramanian | first3 = Kodanallur|doi=10.1080/15287399409531843|pmid=8126750|issn=0098-4108}}</ref><ref name="Callender1993">{{Cite book | title = Neurobehavioral Methods and Effects in Occupational and Environmental Health|chapter=Three-Dimensional Brain Metabolic Imaging in Patients with Toxic Encephalopathy. Presented at the Fourth International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health, July 8–11, 1991, Tokyo, Japan. | date = 1994-01-01|url=https://www.sciencedirect.com/science/article/pii/B9780120597857500478 | pages = 451–475 | last = Callender | first = Thomas J. | authorlink = | last2 = Morrow | first2 = Lisa | authorlink2 = | last3 = Subramanian | first3 = Kodanallur | authorlink3 = | last4 = Duhon | first4 = Dan | authorlink4 = | last5 = Ristovv | first5 = Mona | authorlink5 = |isbn=978-0-12-059785-7|language=en|publisher=Academic Press | editor-last = Araki|editor-first = Shunichi|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Heuser1994">{{Cite journal | title = NeuroSPECT findings in patients exposed to neurotoxic chemicals | date = 1994-07-01|url=https://europepmc.org/article/med/7778114|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 561–571 | last = Heuser | first = G | last2 = Mena | first2 = I | last3 = Alamos | first3 = F|pmid=7778114|issn=1477-0393}}</ref><ref name="Hillert2007">{{Cite journal | title = Odor processing in multiple chemical sensitivity | date = 2007 | url=https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266|journal=Human Brain Mapping|volume=28|issue=3|pages=172–182 | last = Hillert | first = Lena | last2 = Musabasic | first2 = Vildana | last3 = Berglund | first3 = Hans | last4 = Ciumas | first4 = Carolina | last5 = Savic | first5 = Ivanka|language=en|doi=10.1002/hbm.20266|pmc=PMC6871299|pmid=16767766|issn=1097-0193}}</ref><ref name="Ross1999-neurotoxic">{{Cite journal | title = Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities† | date = 1999-04-01|url=https://doi.org/10.1177/074823379901500316|journal=Toxicology and Industrial Health|volume=15|issue=3-4 | pages = 415–420 | last = Ross | first = Gerald H. | last2 = Rea | first2 = William J. | last3 = Johnson | first3 = Alfred R. | last4 = Hickey | first4 = David C. | last5 = Simon | first5 = Theodore R.|language=en|doi=10.1177/074823379901500316|issn=0748-2337}}</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name="ch1.4" /><ref name="Alessandrini2016">{{Cite journal | title = Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity | date = 2016-03-01|url=https://doi.org/10.1007/s10548-015-0453-3|journal=Brain Topography|volume=29|issue=2|pages=243–252 | last = Alessandrini | first = Marco | last2 = Micarelli | first2 = Alessandro | last3 = Chiaravalloti | first3 = Agostino | last4 = Bruno | first4 = Ernesto | last5 = Danieli | first5 = Roberta | last6 = Pierantozzi | first6 = Mariangela | last7 = Genovesi | first7 = Giuseppe | last8 = Öberg | first8 = Johanna | last9 = Pagani | first9 = Marco | last10 = Schillaci | first10 = Orazio|language=en|doi=10.1007/s10548-015-0453-3|issn=1573-6792}}</ref><ref name="Chiaravalloti2015">{{Cite journal | title = Cortical activity during olfactory stimulation in multiple chemical sensitivity: a 18F-FDG PET/CT study | date = 2015-04-01|url=https://doi.org/10.1007/s00259-014-2969-2|journal=European Journal of Nuclear Medicine and Molecular Imaging|volume=42|issue=5 | pages = 733–740 | last = Chiaravalloti | first = Agostino | last2 = Pagani | first2 = Marco | last3 = Micarelli | first3 = Alessandro | last4 = Di Pietro | first4 = Barbara | last5 = Genovesi | first5 = Giuseppe | last6 = Alessandrini | first6 = Marco | last7 = Schillaci | first7 = Orazio|language=en|doi=10.1007/s00259-014-2969-2|issn=1619-7089}}</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018" />{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name="ch1.4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref name="Albright1992">{{Cite journal | title = Is There Evidence of an Immunologic Basis for Multiple Chemical Sensitivity? | date = Sep 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800420|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=215–219 | last = Albright | first = Joseph F. | authorlink = | last2 = Goldstein | first2 = Robert A. | authorlink2 = |doi=10.1177/074823379200800420|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref><ref name="Meggs1992">{{Cite journal | title = Multiple Chemical Sensitivities and the Immune System | date = Jul 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800419|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=203–214 | last = Meggs | first = William J. | authorlink = |doi=10.1177/074823379200800419|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref name="Labarge2000">{{Cite journal | title = Multiple Chemical Sensitivity: A Review of the Theoretical and Research Literature | date = 2000-12-01|url=https://doi.org/10.1023/A:1026460726965|journal=Neuropsychology Review|volume=10|issue=4|pages=183–211 | last = Labarge | first = Andrew S. | last2 = McCaffrey | first2 = Robert J.|language=en|doi=10.1023/A:1026460726965|issn=1573-6660}}</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name="ch1.4" /><ref name="Belpomme2015">{{Cite journal | title = Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder | date = 2015-12-01|url=https://www.degruyter.com/document/doi/10.1515/reveh-2015-0027/html|journal=Reviews on Environmental Health|volume=30|issue=4|pages=251–271 | last = Belpomme | first = Dominique | last2 = Campagnac | first2 = Christine | last3 = Irigaray | first3 = Philippe|language=en|doi=10.1515/reveh-2015-0027|issn=2191-0308}}</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name="ch1.4" /><ref name="Belpomme2015" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref name="ch3.11">{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="Hrda2010">{{Cite journal | title = The role of environmental factors in autoimmune thyroiditis | date = 2010 | url=https://pubmed.ncbi.nlm.nih.gov/20588228/|journal=Neuro Endocrinology Letters|volume=31|issue=3|pages=283–289 | last = Hybenova | first = Monika | last2 = Hrda | first2 = Pavlina | last3 = Procházková | first3 = Jarmila | last4 = Stejskal | first4 = Vera | last5 = Sterzl | first5 = Ivan|pmid=20588228|issn=0172-780X}}</ref><ref name="Ziem1997">{{Cite journal | title = Profile of patients with chemical injury and sensitivity. | date = 1997-03-01|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 417–436 | last = Ziem | first = G. | last2 = McTamney | first2 = J.|doi=10.1289/ehp.97105s2417|pmc=PMC1469804|pmid=9167975}}</ref><ref name="Nogue2007">{{Cite journal | title = Sensibilidad química múltiple: análisis de 52 casos | date = 2007-06-01|url=https://doi.org/10.1157/13107370|journal=Medicina clinica|volume=129|issue=3 | pages = 96–9 | last = Nogué | first = Santiago | authorlink = | last2 = Fernández-Solá | first2 = Joaquim | authorlink2 = | last3 = Rovira | first3 = Elisabet | authorlink3 = | last4 = Montori | first4 = Elisabet | authorlink4 = | last5 = Fernández-Huerta | first5 = José Manuel | authorlink5 = | last6 = Munné | first6 = Pere | authorlink6 = |language=es|doi=10.1157/13107370|pmc=|pmid=17594860|access-date=|trans-title=Multiple chemical sensitivity: study of 52 cases|issn=1578-8989|quote=|via=}}</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychosomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has psychological causes has flaws.<ref name="TaskForce2017" /><ref name="ch1.4" /><ref name="Genuis2013" /><ref name="Tuuminen2018">{{Cite journal | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives | date = Aug 2018|url=https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=8|pages=e429 | last = Tuuminen | first = Tamara | authorlink = |language=en-US|doi=10.1097/JOM.0000000000001369|pmc=|pmid=|access-date=|issn=1076-2752|quote=|via=}}</ref><ref name="Davidoff1994">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Fogarty | first2 = L. | authorlink2 = | date = Sep 1994 | title = Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Bransfield2019">{{Cite journal | title = Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty | date = 2019-10-08|url=https://doi.org/10.3390/healthcare7040114|journal=Healthcare|volume=7|issue=4|pages=114 | last = Bransfield | last2 = Friedman|doi=10.3390/healthcare7040114|pmc=PMC6955780|pmid=31597359|issn=2227-9032}}</ref><ref name="Steinemann2018" /><ref name="Davidoff1996">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Keyl | first2 = P.M. | authorlink2 = | date = May 1996 | title = Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group | url =https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

The arguments used to support the hypothesis that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref name="Gots1995">{{Cite journal | last = Gots | first = Ronald E. | date = 1995-01-01 | title = Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref name="Hainge2003">{{citation | first =Kimberly | last = Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf | work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1 | date =Fall 2003 | title = Multiple chemical sensitivity|pages=3|edition=}}</ref>
# that nocebo responses may operate in MCS,<ref name="Binkley1997">{{Cite journal | last = Binkley | first = K | author-link = | last2 = Kutcher | first2 = S | authorlink2 = | date = Apr 1997 | title = Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4 | pages = 570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref name="Witthoft2008">[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref name="Bailer2005">{{Cite journal | title = Evidence for overlap between idiopathic environmental intolerance and somatoform disorders | date = Nov 2005|url=https://pubmed.ncbi.nlm.nih.gov/16314597|journal=Psychosomatic Medicine|volume=67|issue=6 | pages = 921–929 | last = Bailer | first = Josef | author-link = | last2 = Witthöft | first2 = Michael | authorlink2 = | last3 = Paul | first3 = Christine | authorlink3 = | last4 = Bayerl | first4 = Christiane | authorlink4 = | last5 = Rist | first5 = Fred | authorlink5 = |doi=10.1097/01.psy.0000174170.66109.b7|pmc=|pmid=16314597|access-date=|issn=1534-7796|quote=|via=}}</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name="ch1.4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (e.g. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name="ch1.4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name="ch1.4" /><ref name="Davidoff1994" /><ref name="Davidoff1996" />

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name="TaskForce2017" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref name="Gibson2011-doc">{{Cite journal | title = Physicians' perceptions and practices regarding patient reports of multiple chemical sensitivity | date = 2011 |url=https://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf | journal=ISRN nursing|volume=2011|issue= | pages = 838930 | last = Gibson | first = Pamela Reed | authorlink = | last2 = Lindberg | first2 = Amanda | authorlink2 = |doi=10.5402/2011/838930|pmc=3168894|pmid=22007328|access-date=|issn=2090-5491|quote=|via=}}</ref><ref name="Gibson2009" /><ref name="MCS-EI">{{Cite web | title = MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]|url-status=dead | url =https://www.counselingatcela.com/mcs-and-eis|archive-date = 2020-10-21|archive-url=https://web.archive.org/web/20201021235254/https://www.counselingatcela.com/mcs-and-eis|website=The Counseling Center at CELA|quote=Is MCS a mental illness? MCS is not a mental illness}}</ref><ref name="PMC2821254">{{Cite journal | last = Lavergne | first = M. Ruth | authorlink = | last2 = Cole | first2 = Donald C. | authorlink2 = | last3 = Kerr | first3 = Kathleen | authorlink3 = | last4 = Marshall | first4 = Lynn M. | authorlink4 = | date = Feb 2010 | title = Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal | last = Caress | first = Stanley M | authorlink = | last2 = Steinemann | first2 = Anne C | authorlink2 = | date = 2003-09-01 | title = A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref name="Brussels2015">''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of May 18, 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref name="nocebohh">{{citation |url = https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response | website = Harvard Health. Harvard Medical School blog | date = Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref name="Bittar2015">{{Cite journal | last = Bittar | first = Caroline | authorlink = | last2 = Nascimento | first2 = Osvaldo J.M. | authorlink2 = | date = Jan 2015 | title = Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1 | pages = 58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name="TaskForce2017" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref name="DSM-5">{{Cite book | title = Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|language=|title-link=|url= | date = May 15, 2014|publisher=American Psychiatric Press | last = American Psychiatric Association | first = | authorlink = |oclc=|quote=|archive-url=|archive-date=|location=Washington, D.C}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref name="icd10cm-f45.8">{{Citation | url =https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 | title = Other somatoform disorders {{!}} ICD-10-CM Diagnosis Code F45.8 | date = 2020 | website = ICD-10-CM}}</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name="TaskForce2017" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name="ch1.4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name="ch1.4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name="ch1.4" /><ref name=":23">{{Cite journal | title = Role of Polymorphisms of Inducible Nitric Oxide Synthase and Endothelial Nitric Oxide Synthase in Idiopathic Environmental Intolerances | date = 2015-03-24|url=https://www.hindawi.com/journals/mi/2015/245308/|journal=Mediators of Inflammation|volume=2015 |pages=e245308 | last = De Luca | first = Chiara | last2 = Gugliandolo | first2 = Agnese | last3 = Calabrò | first3 = Carlo | last4 = Currò | first4 = Monica | last5 = Ientile | first5 = Riccardo | last6 = Raskovic | first6 = Desanka | last7 = Korkina | first7 = Ludmila | last8 = Caccamo | first8 = Daniela|language=en|doi=10.1155/2015/245308|issn=0962-9351}}</ref><ref name=":24">{{Cite journal | title = Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses | date = 2016-01-15|url=https://www.sciencedirect.com/science/article/pii/S0024320515301211|journal=Life Sciences|volume=145|pages=27–33 | last = Gugliandolo | first = Agnese | last2 = Gangemi | first2 = Chiara | last3 = Calabrò | first3 = Carlo | last4 = Vecchio | first4 = Mercurio | last5 = Di Mauro | first5 = Debora | last6 = Renis | first6 = Marcella | last7 = Ientile | first7 = Riccardo | last8 = Currò | first8 = Monica | last9 = Caccamo | first9 = Daniela|language=en|doi=10.1016/j.lfs.2015.12.028|issn=0024-3205}}</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name="ch1.4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">{{Cite journal | title = The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances | date = Jul 2011|url=https://www.mdpi.com/1660-4601/8/7/2770|journal=International Journal of Environmental Research and Public Health|volume=8|issue=7|pages=2770–2797 | last = De Luca | first = Chiara | authorlink = | last2 = Raskovic | first2 = Desanka | authorlink2 = | last3 = Pacifico | first3 = Valeria | authorlink3 = | last4 = Thai | first4 = Jeffrey Chung Sheun | authorlink4 = | last5 = Korkina | first5 = Liudmila | authorlink5 = |doi=10.3390/ijerph8072770|pmc=3155329|pmid=21845158|access-date=|issn=1660-4601|quote=|via=}}</ref><ref name="Caccamo2013">{{Cite journal | title = Xenobiotic sensor- and metabolism-related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population | date = 2013 |url=https://downloads.hindawi.com/journals/oximed/2013/831969.pdf | journal=Oxidative Medicine and Cellular Longevity|volume=2013|issue= | pages = 831969 | last = Caccamo | first = Daniela | authorlink = | last2 = Cesareo | first2 = Eleonora | authorlink2 = | last3 = Mariani | first3 = Serena | authorlink3 = | last4 = Raskovic | first4 = Desanka | authorlink4 = | last5 = Ientile | first5 = Riccardo | authorlink5 = | last6 = Currò | first6 = Monica | authorlink6 = | last7 = Korkina | first7 = Liudmila | last8 = De Luca | first8 = Chiara|doi=10.1155/2013/831969|pmc=3725911|pmid=23936614|access-date=|issn=1942-0994|quote=|via=}}</ref><ref name="Luca2014-metabolic">{{Cite journal | title = Metabolic and Genetic Screening of Electromagnetic Hypersensitive Subjects as a Feasible Tool for Diagnostics and Intervention | date = 2014-04-09|url=https://www.hindawi.com/journals/mi/2014/924184/|journal=Mediators of Inflammation|volume=2014|pages=e924184 | last = De Luca | first = Chiara | last2 = Chung Sheun Thai | first2 = Jeffrey | last3 = Raskovic | first3 = Desanka | last4 = Cesareo | first4 = Eleonora | last5 = Caccamo | first5 = Daniela | last6 = Trukhanov | first6 = Arseny | last7 = Korkina | first7 = Liudmila|language=en|doi=10.1155/2014/924184|issn=0962-9351}}</ref> including polymorphisms and differences in expression of the following: [[Cytochrome P450 2D6|CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref name="Attis2019">{{Cite web|url=https://www.karger.com/Article/FullText/497322 | title = Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity | last = D'Attis | first = S | authorlink = | last2 = Massari | first2 = S | authorlink2 = | date = 2019 | website = |pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14 | last3 = Mazzei | first3 = F | last4 = Maio | first4 = D | last5 = Bozzetti | first5 = MP | last6 = Vergallo | first6 = I | last7 = Mauro | first7 = S | last8 = Minelli | first8 = M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V|title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR|volume = 33|issue = 5 |pages = 971–8 |pmid = 15256524 |doi = 10.1093/ije/dyh251|journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251 | last = | first = | last2 = | first2 = | date = 2004|pmc=|quote= | last7 = | first7 = |via=}}</ref><ref name="Schnackenberget">{{Cite journal | last = Schnakenberg | first = Eckart | last2 = Fabig | first2 = Karl-Rainer | last3 = Stanulla | first3 = Martin | last4 = Strobl | first4 = Nils | last5 = Lustig | first5 = Michael | last6 = Fabig | first6 = Nathalie | last7 = Schloot | first7 = Werner | date = 2007-02-10 | title = A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1 | pages = 6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name="ch1.4" />
===COVID-19 and Long COVID===
There have been anecdotal reports of people with [[Long COVID]], or chronic COVID, developing new allergies, including fragrance and other chemical sensitivities.<ref name="Davis2021">{{Cite journal | last = Davis | first = Hannah | authorlink = Hannah Davis | last2 = Assaf | first2 = Gina | authorlink2 = Gina Assaf | last3 = McCorkell | first3 = Lisa | authorlink3 = | last4 = Wei | first4 = Hannah | authorlink4 = | last5 = Low | first5 = Ryan | authorlink5 = | last6 = Re’em | first6 = Yochai | authorlink6 = | last7 = Redfield | first7 = Signe | last8 = Austin | first8 = Jared | last9 = Akrami | first9 = Athena | date = 2020 | title=Characterizing Long COVID in an International Cohort: 7 Months of Symptoms and Their Impac|url=https://europepmc.org/article/PPR/PPR258069|journal=medRxiv|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/ | title = Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation | last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers | last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain | last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir | last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson | last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas | last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner | last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested | last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry | last9 =Joshi | first9 = Pradip | authorlink9 = Pradip Joshi | last10 = Powles | first10 = AC Peter | authorlink10 = A C Peter Powles | last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey | last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | pages = 7-115 | date = 2003 | pmid = | doi = 10.1300/J092v11n01_02 | url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf}}</ref><ref name="ICC2011primer">{{citation | last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers | last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande | last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir | last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas | last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick | last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell | last7 = Staines | first7 = D | authorlink7 = Donald Staines | last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles | last9 = Speight | first9 = N | authorlink9 = Nigel Speight | last10 = Vallings | first10 = R | authorlink10 = Rosamund Vallings | last11 = Bateman | first11 = L | authorlink11 = Lucinda Bateman | last12 = Bell | first12 = DS | authorlink12 = David Bell | last13 = Carlo-Stella | first13 = N | authorlink13 = Nicoletta Carlo-Stella | last14 = Chia | first14 = J | authorlink14 = John Chia | last15 = Darragh | first15 = A | authorlink15 = Austin Darragh | last16 = Gerken | first16 = A | authorlink16 = Anne Gerken | last17 = Jo | first17 = D | authorlink17 = Daehyun Jo | last18 = Lewis | first18 = DP | authorlink18 = Donald Lewis | last19 = Light | first19 = AR | authorlink19 = Alan Light | last20 = Light | first20 = KC | authorlink20 = Kathleen Light | last21 = Marshall-Gradisnik | first21 = S | authorlink21 = Sonya Marshall-Gradisnik | last22 = McLaren-Howard | first22 = J | authorlink22 = John McLaren-Howard | last23 = Mena | first23 = I | authorlink23 = Ismael Mena | last24 = Miwa | first24 = K | authorlink24 = Kunihisa Miwa | last25 = Murovska | first25 = M | authorlink25= Modra Murovska | last26 = Stevens | first26 = SR | authorlink26 = Staci Stevens | title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners | date = 2012| isbn = 978-0-9739335-3-6 | url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf }}</ref>
# The [[Canadian Consensus Criteria]] (2003) for ME/CFS lists "[[New allergies and intolerances|new sensitivities to food, medications and/or chemicals]]" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for Myalgic Encephalomyelitis lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# The U.S. ME/CFS Clinician Coalition publication '''Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) (2020)''' lists "chemical sensitivity" as a symptom of ME/CFS, and MCS as a comorbidity.<ref name="USMECFS-2020">{{Cite web | last = U.S. ME/CFS Clinician Coalition | date = Jul 2020 | url = https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view | title = Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms
== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the [[real illness|reality of the illness]].<ref name="Oreskes2011">{{Cite book | title = Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=| date = 2011 |publisher=Bloomsbury | last = Oreskes | first = Naomi | authorlink = | last2 = Conway | first2 = Erik M. | authorlink2 = |quote=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">{{Cite web|website=Deadline | first =
Erik | last = Pedersen | url =https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ | title = Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs" | date = Aug 17, 2019|quote=a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.}}</ref><ref name="Dusenberry">{{cite web | last = Dusenberry | first = Maya. |url=https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science | title = An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science|publisher=PS Mag | date = Sep 20, 2018|quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers-including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care... and add to the stigma and social isolation of an already profoundly marginalized group of people.'}}</ref><ref name="wp-talk">{{Cite web | title = Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref name="WP-cap">{{Cite web|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ | title = Wikipedia captured by skeptics|website=Skeptics about skeptics|access-date=Feb 12, 2020|quote=Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained.}}</ref><ref name="rampantharassment">{{Citation | url =http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ | title = Rampant Harassment on Wikipedia | last = Skeptical About Skeptics | first = | authorlink = | date = | website = Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation | last = Bundrant | first = Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog | date = Apr 15, 2015 |access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url = https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog | date = Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="Steinemann2018" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name="TaskForce2017" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref name="siege2013">{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege | date = Jun 26, 2013|quote="In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."}}</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last = Gale | first =Richard | last2 = Null | first2 = Gary | title = Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network | date = Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref name="Lees1998">{{citation | first = Paul R | last = Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog | date = Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last = Gavura | first = Scott | title = Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog | date = Jul 3, 2014}}</ref><ref name="LeesMold2002">{{citation|last =Lees-Haley|first =Paul R. | title=Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog | date = Dec 23, 2002}}</ref><ref name="Probe1999">{{citation | title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03 | date = Jan 1, 1999 | last = D.R.Z.}}</ref><ref name="Hall-Rea">{{citation | last = Hall | first = Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref name="MacBeth2018">{{citation|last =MacBeth | first = Braden|title = Afflicted and the Tragedy of Fake Illnesses | date = Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref name="BarrettQuestionable">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Questionable Organizations: An Overview | date = Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref name="BarrettVulberability">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Vulnerability to Quackery | date = Jan 16, 2019}}</ref><ref name="Barrett-AAEM">{{Citation | last = Barrett | first = Stephen | title = Regulatory Actions against AAEM Members|publisher=Quackwatch blog | date = Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref name="BarrettOilyphyria">{{Citation | last = Barrett | first = Stephen | title = The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog | date = Jan 22, 2010}}</ref><ref name="BarrettProclam">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = MCS Proclamations}}</ref><ref name="BarrettGWI-MCS">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | first2 = Ronald E | last2 = Gots | title = Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref name="BarrettFad">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Be Wary of "Fad" Diagnoses | date = Oct 6, 2018}}</ref><ref name="BarrettIndex">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis? | date = Mar 28, 2019}}</ref><ref name="BarrettCloseLook">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = A Close Look at "Multiple Chemical Sensitivity" | date = 1998}}</ref><ref name="resolution21">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity | date = Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Multiple Chemical Sensitivity: A Spurious Diagnosis | date = Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref name="CaseWP2009">{{citation | url =https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf | title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York | date = Nov 24, 2009}}</ref><ref name="WP-cap" /><ref name=":20">{{citation|last = Gale | first =Richard | title = Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url = http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network | date = Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref name="NcCarthyism">{{Cite web|url=https://prn.fm/stephen-barrett-medical-mccarthyism/ | title = Stephen Barrett and Medical McCarthyism|website=The Progressive Radio network blog|access-date= Feb 21, 2020}}</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name="ch1.4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref name="siege2013"/> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name="TaskForce2017" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name="Schwenk2004" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name="NICNAS" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name="Ch4.1-Noharm" /><ref name="VictorianHosp" /><ref name="NSW-factsheet" /><ref name="Mercy1999" /><ref name="Hosp2017" /><ref name="canberra2018" /><ref name="WA2019" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name="Aus-HR">{{citation | date = 2007 | title=Australian Human Rights Commission Access: Guidelines and information | last = Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation | last =Michaels | first = Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf | title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization | date = 2013 |quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>
==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ | title = "Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films | last = | first = | date = Nov 25, 2015 | website = YouTube | archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10 | title = Todd Haynes and Julianne Moore on Safe | last = | first = | date = |website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation | title = The 1995 film ‘Safe’ has new meaning during our coronavirus isolation | last = Di Corpo | first = Ryan | authorlink= | date = April 11, 2020 | website = |archive-url=|archive-date=|access-date = December 31, 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url = https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries | date = Sep 18, 2018}}</ref>
==Notable studies and publications==
*1987, Cullen, M.R. The worker with multiple chemical sensitivities: An overview<ref name="Cullen1987">{{Cite journal | title = The worker with multiple chemical sensitivities: an overview | date = Oct 1987|url=https://pubmed.ncbi.nlm.nih.gov/3313760/|journal=Occupational Medicine (Philadelphia, Pa.)|volume=2|issue=4 | pages = 655–661 | last = Cullen | first = M.R. | authorlink = |doi=|pmc=|pmid=3313760|access-date=|issn=0885-114X|quote=|via=}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/3313760 (Abstract)]

*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2005, Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref> - [https://www.sciencedirect.com/science/article/pii/S1438463905000210 (Abstract)]

*2014, Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity<ref name="Horowitz2014">{{Cite journal | title = Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity | date = Apr 2014|url=https://www.liebertpub.com/doi/pdf/10.1089/act.2014.20201|journal=Alternative and Complementary Therapies|volume=20|issue=2 | pages = 96–100 | last = Horowitz | first = Sala | authorlink = |doi=10.1089/act.2014.20201|pmc=|pmid=|access-date=|issn=1076-2809|quote=|via=}}</ref> [https://www.niehs.nih.gov/news/assets/docs_a_e/download_background_material_toxicantinduced_loss_of_tolerance_by_claudia_miller_508.pdf (Full text)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2016">{{Cite journal | last = | first = | authorlink = |vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al. | date = 2016-12-09 | title = Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives<ref name="Rossi2018" /> - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal | last = Viziano | first1 = A. | last2 = Micarelli | first2 = A. | last3 = Pasquantonio | first3 = G. | last4 = Della-Morte | first4 = D. | last5 = Alessandrini | first5 = M. | date = Nov 2018 | title = Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8 | pages = 923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]

*2019, International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products<ref name="Steinemann2019-international" /> - [https://link.springer.com/article/10.1007/s11869-019-00672-1 (Full text)]
*2021, Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity<ref name="Mazzatenta2021">{{Cite journal | title = Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity | date = 2021 | url=https://onlinelibrary.wiley.com/doi/abs/10.14814/phy2.15034|journal=Physiological Reports|volume=9|issue=18|pages=e15034 | last = Mazzatenta | first = Andrea | last2 = Pokorski | first2 = Mieczyslaw | last3 = Giulio | first3 = Camillo Di|language=en|doi=10.14814/phy2.15034|pmc=PMC8449310|pmid=34536058|issn=2051-817X}}</ref> - [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 (Full text)]
*2021, Mast cell activation may explain many cases of chemical intolerance<ref name="Miller2021">{{Cite journal | title = Mast cell activation may explain many cases of chemical intolerance | date = 2021-11-17|url=https://doi.org/10.1186/s12302-021-00570-3|journal=Environmental Sciences Europe|volume=33|issue=1|pages=129 | last = Miller | first = Claudia S. | last2 = Palmer | first2 = Raymond F. | last3 = Dempsey | first3 = Tania T. | last4 = Ashford | first4 = Nicholas A. | last5 = Afrin | first5 = Lawrence B.|language=en|doi=10.1186/s12302-021-00570-3|issn=2190-4715}}</ref> [https://link.springer.com/article/10.1186/s12302-021-00570-3 (Full text)]
*2021, Multiple Chemical Sensitivity<ref name="Zucco2021">{{Cite journal | title = Multiple Chemical Sensitivity | date = 2021-12-29|url=https://www.mdpi.com/2076-3425/12/1/46/htm|journal=Brain Sciences|volume=12|issue=1 | pages = 46 | last = Zucco | first = Gesualdo M. | last2 = Doty | first2 = Richard L.|doi=10.3390/brainsci12010046|issn=2076-3425}}</ref> [https://www.mdpi.com/2076-3425/12/1/46/htm (Full text)]

==News articles and interviews ==
*2017, [https://web.archive.org/web/20200215070226/https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world] - New Zealand Listener

*2018, [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condtion that affects one million Australia] - SBS television, Australia (Video)
*2019, [https://www.theguardian.com/lifeandstyle/2019/sep/15/fragrance-sensitivity-why-perfumed-products-can-cause-profound-health-problems Fragrance sensitivity: why perfumed products can cause profound health problems] - The Guardian

*2020, [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds] - Melbourne University Press
*2020, [https://i.stuff.co.nz/life-style/homed/kitchen/300272316/are-scented-cleaning-products-making-you-sick Are scented cleaning products making you sick?] - Stuff NZ
*2021, [https://www.washingtonpost.com/health/medical-mysteries/headache-chemical-smell-medical-mystery/2021/09/24/16c427ea-f2ec-11eb-a49b-d96f2dac0942_story.html The unusual headaches that upended this man's life began with a new car] - The Washington Post
*2021, [https://www.smh.com.au/national/experts-disturbed-over-toxic-discovery-in-popular-makeup-products-20210626-p584k2.html Experts ‘disturbed’ over toxic discovery in popular makeup products]<ref name="Whitehead2021">{{Cite journal | title = Fluorinated Compounds in North American Cosmetics | date = 2021-07-13|url=https://doi.org/10.1021/acs.estlett.1c00240|journal=Environmental Science & Technology Letters|volume=8|issue=7 | pages = 538–544 | last = Whitehead | first = Heather D. | last2 = Venier | first2 = Marta | last3 = Wu | first3 = Yan | last4 = Eastman | first4 = Emi | last5 = Urbanik | first5 = Shannon | last6 = Diamond | first6 = Miriam L. | last7 = Shalin | first7 = Anna | last8 = Schwartz-Narbonne | first8 = Heather | last9 = Bruton | first9 = Thomas A. | last10 = Blum | first10 = Arlene | last11 = Wang | first11 = Zhanyun|doi=10.1021/acs.estlett.1c00240}}</ref> - Sydney Morning Herald

== See also ==
* [[Toxicant-induced loss of tolerance (TILT)]]
* [[Mast cell activation syndrome]]
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[New allergies and intolerances]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf | title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome | last = Williams | first = Margaret | authorlink = Margaret Williams | date = Nov 10, 2010 | website = margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals
== References ==
{{reflist}}

[[Category:Allergy signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2024-11-24T20:14:18Z

Aletheia2020:/* Signs and symptoms */ corrections proposed in discussion

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal | last = Rossi | first = Sabrina | authorlink = | last2 = Pitidis | first2 = Alessio | authorlink2 = | date = Feb 2018 | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{Cite book | url =|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|chapter-url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS | first = |location=Università degli Studi di Milano, Italy | date = 2019-05-23|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and [[mold]].<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="1.2-trigger">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
==Signs and symptoms ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal| year = 1999 | title = Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /> and symptoms range from mild to severely disabling,<ref name="Ch1" /><ref name="NICNAS" /><ref name="TaskForce2017">{{Citation | last = Task Force on Environmental Health | date = 2017 | url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf | title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal | last = Steinemann | first = Anne | authorlink = | date = Mar 2018 | title = National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name="TaskForce2017" /><ref name="Loria2017">{{Cite journal | last = Loria-Kohen | first = Viviana | last2 = Marcos-Pasero | first2 = Helena | last3 = de la Iglesia | first3 = Rocío | last4 = Aguilar-Aguilar | first4 = Elena | last5 = Espinosa-Salinas | first5 = Isabel | last6 = Herranz | first6 = Jesús | last7 = Ramírez de Molina | first7 = Ana | last8 = Reglero | first8 = Guillermo | date = 2017-08-22 | title = Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref name="Gibson2016-unmet">{{Cite journal | last = Gibson | first = Pamela Reed | last2 = Leaf | first2 = Britney | last3 = Komisarcik | first3 = Victoria | date = 2016-01-12 | title = Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5 | pages = 75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref name="García2014">{{Cite journal | last = García-Sierra | first = Rosa | last2 = Álvarez-Moleiro | first2 = María | date = 2014-07-01 | title = Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2 | pages = 95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref name="Alobid2014">{{Cite journal | last = Alobid | first = Isam | last2 = Nogué | first2 = Santiago | last3 = Izquierdo-Dominguez | first3 = Adriana | last4 = Centellas | first4 = Silvia | last5 = Bernal-Sprekelsen | first5 = Manuel | last6 = Mullol | first6 = Joaquim | date = 2014-12-01 | title = Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal | last = Gibson | first = PR | author-link = | last2 = Vogel | first2 = VM | authorlink2 = | date = Jan 2009 | title = Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1 | pages = 72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Koch2006">{{Cite journal | last = Koch | first = Lynn | last2 = Vierstra | first2 = Courtney | last3 = Penix | first3 = Ken | date = 2006-09-01 | title = A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS can include [[headache]], [[migraine]], [[cognitive dysfunction|neurocognitive deficits]], [[dizziness]], [[fatigue]], [[arrhythmia|cardiac arrhythmia]], [[tachycardia]], [[hypotension]], [[hypertension]] (high blood pressure), [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], [[myalgia|muscle]] and [[Arthralgia|joint pain]], [[skin rash]]es, [[hives]], [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name="NICNAS" /><ref name="Valderrama2015" /><ref name="TaskForce2017" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal | last1 = Genuis | first1 = SJ | date = May 2013 | title = Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5 | pages = 572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291 | last2 = Ross | first2 = PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation. | last3 = Whysner | first3 = J | last4 = Covello | first4 = VT | last5 = Kuschner | first5 = M | last6 = Rifkind | first6 = AB | last7 = Sedler | first7 = MJ | last8 = Trichopoulos | first8 = D|via=}}</ref><ref name="Ross1999-Olfaction">{{cite journal|vauthors=Ross PM, Whysner J, Covello VT, Kuschner M, Rifkind AB, Sedler MJ, Trichopoulos D, Williams GM| year = 1999 | title = Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5 | pages = 467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN| year = 1999 | title = A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2 | pages = 73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book |isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp | title = A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs | date = 2010 | last=National Industrial Chemicals Notification and Assessment Scheme | last2 = Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathologies."<ref name="Rossi2018" /> It can be associated with very high levels of disability. [[File:Cosmeticsbottles.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">{{Cite book | title = The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link= | url = |access-date= | date = 2017 | publisher=The text publishing company | last = Grenville | first = Kate | authorlink = |others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne, Australia | editor-last = | editor-first = |editor1-link=|editor-last2 = |editor-first2 = }}</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation |url = https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf | title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety | date = 2009|location=United States | page = 9}}</ref>]]
=== Chemicals that trigger symptoms ===
The following substances are common triggers for adverse symptoms in people with MCS:
* [[pesticide]]s (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic [[fragrance]]s and products containing fragrance (e.g. fragranced deodorant)
* laundry [[detergent]]s and fabric softeners
* [[cigarette smoke]] and woodfire smoke
* [[petrochemical|petrochemical solvents]] and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (e.g. [[tartrazine]])
* some [[medication intolerance|medications]] and anesthetics
* [[air pollution]] (e.g. [[black carbon]], [[nitrogen oxide]], [[ozone]])
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name="NICNAS" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15">{{Cite book | title = [[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]] | last = Pall | first = Martin L. | authorlink = Martin Pall|publisher=Routledge & Harrington Park Press | date = 2007 | isbn=978-0789023896|location=New York}}</ref><ref name="Valderrama2015">{{Cite book | last = Valderrama Rodríguez | first = M | last2 = Revilla López | first2 = MC | last3 = Blas Diez | first3 = MP | last4 = Vázquez Fernández del Pozo | first4 = S | last5 = Martín Sánchez | first5 = Jl | title = Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS) | date = 2015 | trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name="Ziem2018">{{Cite journal | last = Ziem | first = Grace E. | authorlink = | date = 2018-04-24 | title = Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Pigatto2019" />

==Diagnosis and diagnostic criteria ==
Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name="NICNAS" /><ref name="TaskForce2017" />

===International Consensus Criteria 1999===
The 1999 international consensus on MCS is the most commonly used diagnostic criteria for MCS. The consensus is based on the Cullen criteria plus a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /><ref name="pmid10444033" /> MCS is defined as:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book | title = Psychiatry: An evidence-based text | pages = 793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date= | date = 2009-11-27|publisher=CRC Press | last = Hooper | first = Malcolm | authorlink = Malcolm Hooper|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location= | editor-last = Puri | editor-first = Bassant|editor1-link=|editor-last2 = Treasaden|editor-first2 = Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
===Lacour criteria 2005===
# symptom duration of at least 6 months
# symptoms in response to at least 2 of 11 categories of chemical exposures
# at least one [[central nervous system]] symptom is present (eg [[fatigue]], [[headache]]s or [[cognitive dysfunction|neurocognitive deficits]], and one symptom from another organ system
# symptoms causing adjustments of personal lifestyle, or of social or occupational life
# symptoms occurring when exposed and improving or resolving when exposures are removed
# symptoms are triggered by exposure levels that do not induce symptoms in other individuals who are exposed to the same levels<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref><ref name="Tran2013">{{Cite journal | last = Tran | first = Marie Thi Dao | first2 = Lars | last2 = Arendt-Nielsen | first3 = Ron | last3 = Kupers | first4 = Jesper | last4 = Elberling | title = Multiple chemical sensitivity: On the scent of central sensitization|journal=International journal of hygiene and environmental health|volume=216|issue=2|pages=202-210 | date = April 2013|pmid=22487274|url=http://www.bcwomens.ca/Specialized-Services-Site/Documents/Complex%20Chronic%20Diseases%20(CCDP)/Multiple%20Chemical%20Sensitivity%20(journal%20article).pdf | doi=10.1016/j.ijheh.2012.02.010|pmc=|quote=|access-date=|via=}}</ref><ref name="Damiami2021" />
===Diagnostic tools===
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />
===Differential diagnosis ===
A series of tests are needed to identify other potential causes of the symptoms. Particularly important to rule out are:
*[[Porphyria]]s
*[[Mastocytosis]] including systematic mastocytosis<ref name="Damiami2021">{{Cite journal | title = Italian Expert Consensus on Clinical and Therapeutic Management of Multiple Chemical Sensitivity (MCS) | date = 2021-10-27|url=https://doi.org/10.3390/ijerph182111294|journal=International Journal of Environmental Research and Public Health|volume=18|issue=21|pages=11294 | last = Damiani | first = Giovanni | last2 = Alessandrini | first2 = Marco | last3 = Caccamo | first3 = Daniela | last4 = Cormano | first4 = Andrea | last5 = Guzzi | first5 = Gianpaolo | last6 = Mazzatenta | first6 = Andrea | last7 = Micarelli | first7 = Alessandro | last8 = Migliore | first8 = Alberto | last9 = Piroli | first9 = Alba | last10 = Bianca | first10 = Margherita | last11 = Tapparo | first11 = Ottaviano|doi=10.3390/ijerph182111294|pmc=PMC8582949|pmid=34769816|issn=1660-4601}}</ref>

==Prevalence==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" />]] While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="NICNAS" /> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="TaskForce2017" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC | date = May 2004 | title = Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5 | pages = 746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Bloch2007">{{Cite journal | last = Bloch | first = Richard M. | last2 = Meggs | first2 = William J. | date = 2007-01-01 | title = Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression | url =https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref name="Berg2008">{{Cite journal | last = Berg | first = Nikolaj Drimer | last2 = Linneberg | first2 = Allan | last3 = Dirksen | first3 = Asger | last4 = Elberling | first4 = Jesper | date = 2008-07-01 | title = Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population | url =https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7 | pages = 881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref name="Andersson2008">{{Cite journal | last = Andersson | first = Linus | last2 = Johansson | first2 = Åke | last3 = Millqvist | first3 = Eva | last4 = Nordin | first4 = Steven | last5 = Bende | first5 = Mats | date = 2008-10-01 | title = Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5 | pages = 690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}<ref name="Gibson2016-MH">{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM | date = Apr 6, 2016 | title = Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf | journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Rossi2018" />

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305 | last = Steinemann | first = AC | title = A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health | date = 2005|volume=59|issue=6|pages=300-5}}</ref><ref name="Caress2009">{{Cite journal | last = Caress | first = SM | last2 = Steinemann | first2 = AC | date = 2009-02-01 | title = Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1 | pages = 71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Steinemann2018" />

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/ | title = Danimarca: nuovo codice per la MCS | last = | first = | authorlink = | date = 2014-10-14 | website = Infoamica|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14|url-status=}}</ref><ref name="Elberling2014-code">{{Cite journal | title = Patienter med symptomer, der er relateret til dufte og kemiske stoffer, kan nu kodes specifikt med Sundhedsvæsenets Klassifikationssystem | date = 2014-05-26|url=https://pubmed.ncbi.nlm.nih.gov/25096843/|journal=Ugeskrift for Laeger|volume=176|issue=11|pages=V10120627 | last = Elberling | first = Jesper | authorlink = | last2 = Bonde | first2 = Jens Peter Ellekilde | authorlink2 = | last3 = Vesterhauge | first3 = Søren | authorlink3 = | last4 = Bang | first4 = Søren | authorlink4 = | last5 = Linneberg | first5 = Allan | authorlink5 = | last6 = Zachariae | first6 = Claus | authorlink6 = | last7 = Johansen | first7 = Jeanne Duus | last8 = Blands | first8 = Jette | last9 = Skovbjerg | first9 = Sine|language=da|doi=|pmc=|pmid=25096843|access-date=|trans-title=A new classification code is available in the Danish health-care classification system for patients with symptoms related to chemicals and scents|issn=1603-6824|quote=|via=}}</ref>

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name="TaskForce2017" />{{Rp|37}}<ref name="CCHS2014">Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

While a 2018 study at the University of Melbourne found that 1 million Australians (6.5% of adults) reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name="Pigatto2019">{{Cite journal | last = Pigatto | first = Paolo D. | last2 = Guzzi | first2 = Gianpaolo | date = 2019-06-01 | title = Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name="Steinemann2018-Aus">{{Cite journal |url=https://www.sciencedirect.com/science/article/pii/S2211335518300457 | last = Steinemann | first = A. | title=Prevalence and effects of multiple chemical sensitivities in Australia|journal=Prev Med Rep | date = 2018 | volume=10|pages=191-4|issue=|doi=10.1016/j.pmedr.2018.03.007|pmc=PMC5984225|pmid=29868366|quote=|access-date=|via=}}</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name="Steinemann2018" /><ref name="Steinemann2018-Aus" />
== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name="Schwenk2004" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name="Schwenk2004" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref name="ICD10-GM">{{Cite book | title = ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&dq=%C3%9Cberempfindlichkeit%20T78.4&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4&f=false|access-date=| date = 2011 |publisher=Deutscher Ärzteverlag | last = World Health Organization | first = | authorlink = World Health Organization | last2 = DIMDI | first2 = | authorlink2 = |veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name="Ch4.1-Noharm" /><ref name="NICNAS" /> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" /> In 2012, Denmark introduced code '''DR688A1''' for ''Symptoms related to chemicals and scents'' (Symptomer relateret til dufte og kemiske stoffer fra SKS), in the [[Medically unexplained physical symptoms|Medically Unexplained Symptoms]], under ''R68.8 Other specified general symptoms and signs''.<ref name="Elberling2014-code" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html | title = Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) | last = Centers for Disease Control | first = | authorlink = Centers for Disease Control and Prevention | date = 2019-11-19 | website = [[Centers for Disease Control and Prevention]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

==Treatment==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name="TaskForce2017" /><ref name="Ch4.1-Noharm">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name="NICNAS" /><ref name="TaskForce2017" /><ref name="Valderrama2015" /><ref name="Ziem2018" /><ref name="Ch4.1-Noharm" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name="NICNAS" /><ref name="Gibson2003">{{cite journal | last = Gibson | first = PR | last2 = Elms | first2 = AN | last3 =Ruding | first3 = LA | date = 2003 | title = Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name="Ch4.1-Noharm" />

There is evidence that some patients with MCS might have [[hypoxia|poor tissue oxygenation]] when exposed to triggers,<ref name="Ch4.5">{{Cite book |chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> perhaps because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal | last = Horvath | first = I. | last2 = Loukides | first2 = S. | last3 = Wodehouse | first3 = T. | last4 = Kharitonov | first4 = S.A. | last5 = Cole | first5 = P.J. | last6 = Barnes | first6 = P.J. | date = 1998-10-01 | title = Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10 | pages = 867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref name="Ewing1993">{{Cite journal | last = Ewing | first = James F. | last2 = Maines | first2 = Mahin D. | date = 1993 | title = Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain | url =https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref name="Gregersen">{{Cite journal | last = Gregersen | first = Per | last2 = Klausen | first2 = Hans | last3 = Elsnab | first3 = Charlotte Uldal | date = 1987 | title = Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up | url =https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures helps some people.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book |trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were:
* face masks (with HEPA and VOC filters)
* portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters), and
* water purifiers.<ref name="Ch4.2" />

== Accessibility needs==
People with MCS typically experience significant access barriers to society and accessing services. They are also commonly subject to stigma and lack of understanding, perhaps because the condition is poorly understood. Nevertheless, it is recognised as a disability. For example, "a growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR" />

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name="TaskForce2017" /><ref name="Grenvillebook" /><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/ | title = Guidelines on the Use of Perfumes and Scented Products | last = | first = | authorlink = | date = | website = University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Steinemann2018-Aus" /><ref name="Flegel2015">{{Cite journal | last = Flegel | first = Ken | last2 = Martin | first2 = James G. | date = 2015-11-03 | title = Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name="stJosephs" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref name="notsosexy">{{Cite web |at=Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern | url =https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf | title=Not so sexy. The health risks of secret ingredients in fragrance | last = The campaign for safe cosmetics|publisher=The Environmental Working Group | date = 2010}}</ref><ref name="Steinemann2019-asthma">{{Cite journal | last = Steinemann | first = Anne | last2 = Goodman | first2 = Nigel | date = 2019-06-01 | title = Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6 | pages = 643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref name="Steinemann2019-international">{{Cite journal | title = International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products | date = 2019-05-01|url=https://doi.org/10.1007/s11869-019-00672-1|journal=Air Quality, Atmosphere & Health|volume=12|issue=5 | pages = 519–527 | last = Steinemann | first = Anne|language=en|doi=10.1007/s11869-019-00672-1|issn=1873-9326}}</ref><ref name="Nazaroff2004">[https://www.sciencedirect.com/science/article/abs/pii/S1352231004002171 Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865]</ref><ref name="Kumar1995">[https://pubmed.ncbi.nlm.nih.gov/7583865 Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433]</ref><ref name="Elberling2004">[https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2133.2004.06251.x?sid=nlm%3Apubmed Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203.]</ref><ref name="Elberling2009">[https://www.sciencedirect.com/science/article/abs/pii/S1438463909000728?via%3Dihub Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.]</ref><ref name="Mendell2007">[https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2007.00478.x Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.]</ref><ref name="Schnuch2010">[https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2009.09510.x Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.]</ref><ref name="Neuenschwander2010">[https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.200900228 Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.]</ref><ref name="Nielsen2010">[https://pubmed.ncbi.nlm.nih.gov/15910405/ Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.]</ref><ref name="Nielsen2002">[https://pubmed.ncbi.nlm.nih.gov/12122569/ Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.]</ref><ref name="Venkatachari2008">[https://pubmed.ncbi.nlm.nih.gov/18688467/ Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.]</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref name="mcs-cv19-quebec">{{Cite web | last = The Environmental Health Association of Quebec | date = 2020 | url=https://aseq-ehaq.ca/en/projects/mcs-covid-19/ | title = Impacts of Covid-19 Health measures on people with multiple chemical sensitivities}}</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common in Canada and Sweden.<ref name="Steinemann2018-Aus" /><ref name="Grenvillebook" /><ref name="TaskForce2017" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name="stJosephs">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref name="ch5">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS | title = [The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23 | first = | authorlink = |volume=|pages=|edition=|isbn=}}</ref><ref name="Mercy1999">{{Cite web|url=http://www.lassentech.com/eimcspro.html | title = Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol | date = Sep 1999|publisher=Mercy Medical Centers New York and California}}</ref><ref name="Fisher2008">[https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.]</ref><ref name="Rea-surgerych">{{Cite book | last = Rea | first = William J. | authorlink = William Rea | date = 1996 | chapter=41 Surgery in the chemically sensitive|volume=IV | title = Chemical Sensitivity Tools of Diagnosis and Methods of Treatment|chapter-url=https://books.google.co.uk/books?id=cbsL8cUnO_EC&lpg=PA2015&pg=PA2803#v=onepage&q&f=true|url=https://books.google.com/books/about/Chemical_Sensitivity.html?id=cbsL8cUnO_EC | editor-last = Environmental Health Center|location=Dallas, Texas|publisher=CRC Press|pages=2803-2850|isbn=0873719654}}</ref><ref name="VictorianHosp">{{citation |url = https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals | title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals | date = Aug 25, 2011|website =Victoria Department of Health}}</ref><ref name="canberra2018">{{Cite web|url = http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx | title = Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities | date = 2018 | last = ACT Department of Health|access-date= | website = | first = Canberra, Australia | authorlink=|archive-url=|archive-date=}}</ref><ref name="NSW-factsheet">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx | title = Fact sheet: Multiple Chemical Sensitivity Disorder | last = NSW Health | first = | authorlink = | date = Sep 2, 2015 | website = NSW Health|archive-url=|archive-date=|access-date=2020-05-14}}</ref><ref name="Hosp2017">{{Cite web | last = Australian Commission on Safety and Quality in Health Care | date = 2017 | url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf | title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name="SA2016">{{Cite web|url = https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf | title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline | date = Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name="WA2019">{{Cite web |url=http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf | title=Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline | date = Sep 14, 2010|publisher=Western Australia Country Health Service.}}</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name="canberra2018" /><ref name="VictorianHosp" /><ref name="WA2019" /><ref name="SA2016" /> As well, some individual hospitals have their own policies for MCS patients.<ref name="Mercy1999" /><ref name="QHC2010">[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== Housing ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref name="amputated-lives">{{Cite book |chapter=The Elusive Search for a Place to Live | title = Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st|volume=|language=|title-link=|chapter-url=http://www.chemicalsensitivityfoundation.org/pdf/amputated-lives-ch2.pdf | url=|access-date= | date = November 20, 2008|publisher=Cumberland Press | last = Johnson | first =Alison | authorlink = |others=|doi=|oclc=|quote=|location=Parramatta, Australia}}</ref><ref name="Homelessness2002" /><ref name="ANRESS-2020">{{citation | title=Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy | date = Sep 2020 | first = Sharyn | last = Martin|pages=2}}</ref><ref name="Gibson2016" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name="ActionPlan2018">{{Cite web |url = https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf | title=An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)|publisher=Final Report of the Task Force on Environmental Health|location=Ottawa, Canada | date = Dec 2018}}</ref>{{Rp|12}}

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name="Homelessness2002">{{Citation | last = Environmental Health Coalition | first = | authorlink = | date = March 11, 2002 | title = Homelessness at critical level for Western Massachusetts chemically injured|publisher=Western Massachusetts|pages=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name="ANRESS-2020" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name="Gibson2016">{{Cite journal | last = Gibson | first = Pamela | authorlink =
| date = 2016-01-01 | title = A Review of the Life Impacts of Environmental Sensitivities | url = |journal=Internal Medicine Review|volume=|issue=May | page = 9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* [[mold illness|mold]]
* carpet
* fumes from paint
* [[pesticide]] residue
* fumes from [nearby] laundry facilities
* fumes from cleaning products in common areas and
* [[cigarette smoke]].<ref name=":3" />
People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name="ActionPlan2018" /> The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.<ref name="ActionPlan2018" /> It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.”<ref name="ActionPlan2018" />{{Rp|7,12,19}}

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name="NICNAS" /><ref name="Schwenk2004">{{Cite journal | last = Schwenk | first = Michael | date = 2004 | title = Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name="NICNAS" /><ref name="Schwenk2004" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name="Schwenk2004" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

==Possible causes==
[[File:MCS-IEI-biomarker-VOCs.png|thumb|'''MCS patients versus controls: VOCs in breath'''<br>
Basal exhaled VOCs data for MCS and controls, acquired with the ORT-VOC, are shown in a density plot.<br>
Source: Mazzatenta et al. (2021). [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 Physiological Reports, 9, e15034].<ref name="Mazzatenta2021" />]]
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name="TaskForce2017" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name="TaskForce2017" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus for the cause of MCS is that it likely has multiple causes: biochemical, neuro-physiological, causes related to the limbic system and perhaps also genetic predisposition.<ref name="ch1.4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018">{{citation | url =https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 | title = Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport | date = Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or divide.

In 2021, a small study by Mazzatenta and colleagues found breath analysis of key [[volatile organic compound]]s (VOCs) differed between MCS patients and healthy controls, raising the possibility that breath analysis may be able to diagnose MCS in future. Breath analysis can already be used to aid diagnosis for some illnesses.<ref name="Mazzatenta2021" />

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

The [[Toxicant-induced loss of tolerance (TILT)|Toxicant-Induced Loss of Tolerance]] (TILT) hypothesis proposed by Miller (1996) uses the name TILT for multiple chemical sensitivity, and describes a two-phase process. First, there is ''either'' a single major exposure to chemicals ''or'' many smaller exposures, which then result in chemical intolerance or ''sensitization''. In the second phase, low or very low levels of exposure to chemicals cause symptoms that did not occur before sensitization.<ref name="Horowitz2014" /> According to the TILT hypothesis, [[Food intolerance|food and medication intolerances]] frequently occur along with chemical sensitivity. Miller (2021) believes that [[Mast cell activation syndrome|Mast Cell Activation Syndrome]] may account for TILT/MCS.<ref name="Miller2021" />

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name="1.2-trigger" /><ref name="NICNAS" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name="ch1.4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15" /><ref name="Pall2011">{{Cite journal | last = Pall | first = Martin L. | authorlink = Martin Pall | last2 = Satterlee | first2 = JD | date = 2001 | title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder |url = https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of [[limbic kindling]], neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="NICNAS" />

A 2019 scientific review said that while further research was required to confirm Pall's theory, his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name="ch1.4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name="Bell1999">{{Cite journal | last = Bell | first = Iris R. | last2 = Baldwin | first2 = Carol M. | last3 = Fernandez | first3 = Mercedes | last4 = Schwartz | first4 = Gary E.R. | date = 1999-04-01 | title = Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name="Bell-kindling">{{Cite journal | last = Bell | first = IR | author-link = | last2 = Rossi | first2 = J | authorlink2 = | last3 = Gilbert | first3 = ME | authorlink3 = | last4 = Kobal | first4 = G | authorlink4 = | last5 = Morrow | first5 = LA | authorlink5 = | last6 = Newlin | first6 = DB | authorlink6 = | last7 = Sorg | first7 = BA | last8 = Wood | first8 = RW | date = 1997-03-01 | title = Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs' theory of neurogenic inflammation.<ref name="Meggs2017">{{Cite journal | last = Meggs | first = William J. | date = 2017-05-09 | title = The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2 | pages = 83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name="ch1.4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref name="Reid2001">{{cite journal | title = Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6 | pages = 604–9|doi=10.1093/aje/153.6.604|pmid=11257069 | last = Reid | first = S | last2 = Hotopf | first2 = M | authorlink2 = Matthew Hotopf | last3 = Hull | first3 = L | last4 = Ismail | first4 = K | last5 = Unwin | first5 = C | last6 = Wessely | first6 = S | authorlink6 = Simon Wessely | date = 2001 | pmc=|quote=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref name="Gronseth2005">{{Cite journal | title = Gulf war syndrome: a toxic exposure? A systematic review | date = 2005-05-01|url=https://doi.org/10.1016/j.ncl.2004.12.011|journal=Neurologic clinics|volume=23|issue=2 | pages = 523–540 | last = Gronseth | first = Gary S|doi=10.1016/j.ncl.2004.12.011|pmid=15757795|issn=1557-9875}}</ref><ref name="VA2014">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf | title=Clinical practice guideline for the management of chronic multisystem illness | last = U.S. Department of Veterans Affairs, Department of Defense | date = Oct 2014}}</ref><ref name="Spelman2012">{{Cite journal | last = Spelman | first = Juliette F. | last2 = Hunt | first2 = Stephen C. | last3 = Seal | first3 = Karen H. | last4 = Burgo-Black | first4 = A. Lucile | date = 2012-09-01 | title = Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name="VA2014" />

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal | last = Rea | first = William J. | date = 2018-06-01 | title = A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin | url =http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6 | pages = 889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref name="Lieberman2006">{{Cite journal | last = Lieberman | first = Allan | last2 = Rea | first2 = William | last3 = Curtis | first3 = Luke | date = 2006-09-01 | title = Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3 | pages = 763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref name="Vojdani2003">{{Cite journal | last = Vojdani | first = Aristo | last2 = Thrasher | first2 = Jack D. | last3 = Madison | first3 = Roberta A. | last4 = Gray | first4 = Michael R. | last5 = Heuser | first5 = Gunnar | last6 = Campbell | first6 = Andrew W. | date = 2003-07-01 | title = Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7 | pages = 421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref name="WHO-Indoor2011">{{Cite book | last = Hänninen | first = Otto O. | authorlink = | date = 2001 | editor-last = Adan | editor-first = Olaf C. G. |editor2-last=Samson| editor2-first = Robert A. | title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal | last = Knibbs | first = Luke D. | authorlink = | last2 = Woldeyohannes | first2 = Solomon | authorlink2 = | last3 = Marks | first3 = Guy B. | authorlink3 = | last4 = Cowie | first4 = Christine T. | authorlink4 = | date = 2018 | title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref name="Quansah2012">{{Cite journal | last = Quansah | first = Reginald | last2 = Jaakkola | first2 = Maritta S. | last3 = Hugg | first3 = Timo T. | last4 = Heikkinen | first4 = Sirpa A M. | last5 = Jaakkola | first5 = Jouni J.K. | date = 2012-11-07 | title = Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref name="Mendell2011">{{Cite journal | last = Mendell | first = Mark J | author-link = | last2 = Mirer | first2 = Anna G | authorlink2 = | last3 = Cheung | first3 = Kerry | authorlink3 = | last4 = Tong | first4 = My | authorlink4 = | last5 = Douwes | first5 = Jeroen | authorlink5 = | date = 2011-06-01 | title = Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6 | pages = 748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "[[dizziness]], [[seizure]]s, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name="Bell1999" /><ref name="Bell-kindling" /><ref name="Meggs2017" /><ref name="Tran2013" />

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name="Meggs2017" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name="ch1.4" /><ref name="Bell1994">{{Cite journal | title = EEG responses to low-level chemicals in normals and cacosmics | date = 1994-07-01|url=https://europepmc.org/article/med/7778120|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 633–643 | last = Schwartz | first = G E | last2 = Bell | first2 = I R | last3 = Dikman | first3 = Z V | last4 = Fernandez | first4 = M | last5 = Kline | first5 = JP | last6 = Peterson | first6 = JM | last7 = Wright | first7 = KP | pmid=7778120|issn=1477-0393}}</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref name="Bell1998">{{Cite journal | title = Differential Resting Quantitative Electroencephalographic Alpha Patterns in Women with Environmental Chemical Intolerance, Depressives, and Normals | date = 1998-03-01|url=https://www.sciencedirect.com/science/article/pii/S000632239700245X|journal=Biological Psychiatry|volume=43|issue=5|pages=376–388 | last = Bell | first = Iris R | last2 = Schwartz | first2 = Gary E | last3 = Hardin | first3 = Elizabeth E | last4 = Baldwin | first4 = Carol M | last5 = Kline | first5 = John P|language=en|doi=10.1016/S0006-3223(97)00245-X|issn=0006-3223}}</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name="ch1.4" /><ref name="Callender1994">{{Cite journal | title = Evaluation of chronic neurological sequelae after acute pesticide exposure using spect brain scans | date = 1994-03-01|url=https://doi.org/10.1080/15287399409531843|journal=Journal of Toxicology and Environmental Health|volume=41|issue=3|pages=275–284 | last = Callender | first = Thomas James | last2 = Morrow | first2 = Lisa | last3 = Subramanian | first3 = Kodanallur|doi=10.1080/15287399409531843|pmid=8126750|issn=0098-4108}}</ref><ref name="Callender1993">{{Cite book | title = Neurobehavioral Methods and Effects in Occupational and Environmental Health|chapter=Three-Dimensional Brain Metabolic Imaging in Patients with Toxic Encephalopathy. Presented at the Fourth International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health, July 8–11, 1991, Tokyo, Japan. | date = 1994-01-01|url=https://www.sciencedirect.com/science/article/pii/B9780120597857500478 | pages = 451–475 | last = Callender | first = Thomas J. | authorlink = | last2 = Morrow | first2 = Lisa | authorlink2 = | last3 = Subramanian | first3 = Kodanallur | authorlink3 = | last4 = Duhon | first4 = Dan | authorlink4 = | last5 = Ristovv | first5 = Mona | authorlink5 = |isbn=978-0-12-059785-7|language=en|publisher=Academic Press | editor-last = Araki|editor-first = Shunichi|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Heuser1994">{{Cite journal | title = NeuroSPECT findings in patients exposed to neurotoxic chemicals | date = 1994-07-01|url=https://europepmc.org/article/med/7778114|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 561–571 | last = Heuser | first = G | last2 = Mena | first2 = I | last3 = Alamos | first3 = F|pmid=7778114|issn=1477-0393}}</ref><ref name="Hillert2007">{{Cite journal | title = Odor processing in multiple chemical sensitivity | date = 2007 | url=https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266|journal=Human Brain Mapping|volume=28|issue=3|pages=172–182 | last = Hillert | first = Lena | last2 = Musabasic | first2 = Vildana | last3 = Berglund | first3 = Hans | last4 = Ciumas | first4 = Carolina | last5 = Savic | first5 = Ivanka|language=en|doi=10.1002/hbm.20266|pmc=PMC6871299|pmid=16767766|issn=1097-0193}}</ref><ref name="Ross1999-neurotoxic">{{Cite journal | title = Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities† | date = 1999-04-01|url=https://doi.org/10.1177/074823379901500316|journal=Toxicology and Industrial Health|volume=15|issue=3-4 | pages = 415–420 | last = Ross | first = Gerald H. | last2 = Rea | first2 = William J. | last3 = Johnson | first3 = Alfred R. | last4 = Hickey | first4 = David C. | last5 = Simon | first5 = Theodore R.|language=en|doi=10.1177/074823379901500316|issn=0748-2337}}</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name="ch1.4" /><ref name="Alessandrini2016">{{Cite journal | title = Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity | date = 2016-03-01|url=https://doi.org/10.1007/s10548-015-0453-3|journal=Brain Topography|volume=29|issue=2|pages=243–252 | last = Alessandrini | first = Marco | last2 = Micarelli | first2 = Alessandro | last3 = Chiaravalloti | first3 = Agostino | last4 = Bruno | first4 = Ernesto | last5 = Danieli | first5 = Roberta | last6 = Pierantozzi | first6 = Mariangela | last7 = Genovesi | first7 = Giuseppe | last8 = Öberg | first8 = Johanna | last9 = Pagani | first9 = Marco | last10 = Schillaci | first10 = Orazio|language=en|doi=10.1007/s10548-015-0453-3|issn=1573-6792}}</ref><ref name="Chiaravalloti2015">{{Cite journal | title = Cortical activity during olfactory stimulation in multiple chemical sensitivity: a 18F-FDG PET/CT study | date = 2015-04-01|url=https://doi.org/10.1007/s00259-014-2969-2|journal=European Journal of Nuclear Medicine and Molecular Imaging|volume=42|issue=5 | pages = 733–740 | last = Chiaravalloti | first = Agostino | last2 = Pagani | first2 = Marco | last3 = Micarelli | first3 = Alessandro | last4 = Di Pietro | first4 = Barbara | last5 = Genovesi | first5 = Giuseppe | last6 = Alessandrini | first6 = Marco | last7 = Schillaci | first7 = Orazio|language=en|doi=10.1007/s00259-014-2969-2|issn=1619-7089}}</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018" />{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name="ch1.4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref name="Albright1992">{{Cite journal | title = Is There Evidence of an Immunologic Basis for Multiple Chemical Sensitivity? | date = Sep 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800420|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=215–219 | last = Albright | first = Joseph F. | authorlink = | last2 = Goldstein | first2 = Robert A. | authorlink2 = |doi=10.1177/074823379200800420|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref><ref name="Meggs1992">{{Cite journal | title = Multiple Chemical Sensitivities and the Immune System | date = Jul 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800419|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=203–214 | last = Meggs | first = William J. | authorlink = |doi=10.1177/074823379200800419|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref name="Labarge2000">{{Cite journal | title = Multiple Chemical Sensitivity: A Review of the Theoretical and Research Literature | date = 2000-12-01|url=https://doi.org/10.1023/A:1026460726965|journal=Neuropsychology Review|volume=10|issue=4|pages=183–211 | last = Labarge | first = Andrew S. | last2 = McCaffrey | first2 = Robert J.|language=en|doi=10.1023/A:1026460726965|issn=1573-6660}}</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name="ch1.4" /><ref name="Belpomme2015">{{Cite journal | title = Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder | date = 2015-12-01|url=https://www.degruyter.com/document/doi/10.1515/reveh-2015-0027/html|journal=Reviews on Environmental Health|volume=30|issue=4|pages=251–271 | last = Belpomme | first = Dominique | last2 = Campagnac | first2 = Christine | last3 = Irigaray | first3 = Philippe|language=en|doi=10.1515/reveh-2015-0027|issn=2191-0308}}</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name="ch1.4" /><ref name="Belpomme2015" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref name="ch3.11">{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="Hrda2010">{{Cite journal | title = The role of environmental factors in autoimmune thyroiditis | date = 2010 | url=https://pubmed.ncbi.nlm.nih.gov/20588228/|journal=Neuro Endocrinology Letters|volume=31|issue=3|pages=283–289 | last = Hybenova | first = Monika | last2 = Hrda | first2 = Pavlina | last3 = Procházková | first3 = Jarmila | last4 = Stejskal | first4 = Vera | last5 = Sterzl | first5 = Ivan|pmid=20588228|issn=0172-780X}}</ref><ref name="Ziem1997">{{Cite journal | title = Profile of patients with chemical injury and sensitivity. | date = 1997-03-01|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 417–436 | last = Ziem | first = G. | last2 = McTamney | first2 = J.|doi=10.1289/ehp.97105s2417|pmc=PMC1469804|pmid=9167975}}</ref><ref name="Nogue2007">{{Cite journal | title = Sensibilidad química múltiple: análisis de 52 casos | date = 2007-06-01|url=https://doi.org/10.1157/13107370|journal=Medicina clinica|volume=129|issue=3 | pages = 96–9 | last = Nogué | first = Santiago | authorlink = | last2 = Fernández-Solá | first2 = Joaquim | authorlink2 = | last3 = Rovira | first3 = Elisabet | authorlink3 = | last4 = Montori | first4 = Elisabet | authorlink4 = | last5 = Fernández-Huerta | first5 = José Manuel | authorlink5 = | last6 = Munné | first6 = Pere | authorlink6 = |language=es|doi=10.1157/13107370|pmc=|pmid=17594860|access-date=|trans-title=Multiple chemical sensitivity: study of 52 cases|issn=1578-8989|quote=|via=}}</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name="TaskForce2017" /><ref name="ch1.4" /><ref name="Genuis2013" /><ref name="Tuuminen2018">{{Cite journal | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives | date = Aug 2018|url=https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=8|pages=e429 | last = Tuuminen | first = Tamara | authorlink = |language=en-US|doi=10.1097/JOM.0000000000001369|pmc=|pmid=|access-date=|issn=1076-2752|quote=|via=}}</ref><ref name="Davidoff1994">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Fogarty | first2 = L. | authorlink2 = | date = Sep 1994 | title = Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Bransfield2019">{{Cite journal | title = Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty | date = 2019-10-08|url=https://doi.org/10.3390/healthcare7040114|journal=Healthcare|volume=7|issue=4|pages=114 | last = Bransfield | last2 = Friedman|doi=10.3390/healthcare7040114|pmc=PMC6955780|pmid=31597359|issn=2227-9032}}</ref><ref name="Steinemann2018" /><ref name="Davidoff1996">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Keyl | first2 = P.M. | authorlink2 = | date = May 1996 | title = Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group | url =https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

The arguments used to support the hypothesis that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref name="Gots1995">{{Cite journal | last = Gots | first = Ronald E. | date = 1995-01-01 | title = Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref name="Hainge2003">{{citation | first =Kimberly | last = Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf | work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1 | date =Fall 2003 | title = Multiple chemical sensitivity|pages=3|edition=}}</ref>
# that nocebo responses may operate in MCS,<ref name="Binkley1997">{{Cite journal | last = Binkley | first = K | author-link = | last2 = Kutcher | first2 = S | authorlink2 = | date = Apr 1997 | title = Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4 | pages = 570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref name="Witthoft2008">[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref name="Bailer2005">{{Cite journal | title = Evidence for overlap between idiopathic environmental intolerance and somatoform disorders | date = Nov 2005|url=https://pubmed.ncbi.nlm.nih.gov/16314597|journal=Psychosomatic Medicine|volume=67|issue=6 | pages = 921–929 | last = Bailer | first = Josef | author-link = | last2 = Witthöft | first2 = Michael | authorlink2 = | last3 = Paul | first3 = Christine | authorlink3 = | last4 = Bayerl | first4 = Christiane | authorlink4 = | last5 = Rist | first5 = Fred | authorlink5 = |doi=10.1097/01.psy.0000174170.66109.b7|pmc=|pmid=16314597|access-date=|issn=1534-7796|quote=|via=}}</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name="ch1.4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (e.g. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name="ch1.4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name="ch1.4" /><ref name="Davidoff1994" /><ref name="Davidoff1996" />

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name="TaskForce2017" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref name="Gibson2011-doc">{{Cite journal | title = Physicians' perceptions and practices regarding patient reports of multiple chemical sensitivity | date = 2011 |url=https://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf | journal=ISRN nursing|volume=2011|issue= | pages = 838930 | last = Gibson | first = Pamela Reed | authorlink = | last2 = Lindberg | first2 = Amanda | authorlink2 = |doi=10.5402/2011/838930|pmc=3168894|pmid=22007328|access-date=|issn=2090-5491|quote=|via=}}</ref><ref name="Gibson2009" /><ref name="MCS-EI">{{Cite web | title = MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]|url-status=dead | url =https://www.counselingatcela.com/mcs-and-eis|archive-date = 2020-10-21|archive-url=https://web.archive.org/web/20201021235254/https://www.counselingatcela.com/mcs-and-eis|website=The Counseling Center at CELA|quote=Is MCS a mental illness? MCS is not a mental illness}}</ref><ref name="PMC2821254">{{Cite journal | last = Lavergne | first = M. Ruth | authorlink = | last2 = Cole | first2 = Donald C. | authorlink2 = | last3 = Kerr | first3 = Kathleen | authorlink3 = | last4 = Marshall | first4 = Lynn M. | authorlink4 = | date = Feb 2010 | title = Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal | last = Caress | first = Stanley M | authorlink = | last2 = Steinemann | first2 = Anne C | authorlink2 = | date = 2003-09-01 | title = A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref name="Brussels2015">''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of May 18, 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref name="nocebohh">{{citation |url = https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response | website = Harvard Health. Harvard Medical School blog | date = Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref name="Bittar2015">{{Cite journal | last = Bittar | first = Caroline | authorlink = | last2 = Nascimento | first2 = Osvaldo J.M. | authorlink2 = | date = Jan 2015 | title = Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1 | pages = 58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name="TaskForce2017" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref name="DSM-5">{{Cite book | title = Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|language=|title-link=|url= | date = May 15, 2014|publisher=American Psychiatric Press | last = American Psychiatric Association | first = | authorlink = |oclc=|quote=|archive-url=|archive-date=|location=Washington, D.C}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref name="icd10cm-f45.8">{{Citation | url =https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 | title = Other somatoform disorders {{!}} ICD-10-CM Diagnosis Code F45.8 | date = 2020 | website = ICD-10-CM}}</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name="TaskForce2017" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name="ch1.4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name="ch1.4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name="ch1.4" /><ref name=":23">{{Cite journal | title = Role of Polymorphisms of Inducible Nitric Oxide Synthase and Endothelial Nitric Oxide Synthase in Idiopathic Environmental Intolerances | date = 2015-03-24|url=https://www.hindawi.com/journals/mi/2015/245308/|journal=Mediators of Inflammation|volume=2015 |pages=e245308 | last = De Luca | first = Chiara | last2 = Gugliandolo | first2 = Agnese | last3 = Calabrò | first3 = Carlo | last4 = Currò | first4 = Monica | last5 = Ientile | first5 = Riccardo | last6 = Raskovic | first6 = Desanka | last7 = Korkina | first7 = Ludmila | last8 = Caccamo | first8 = Daniela|language=en|doi=10.1155/2015/245308|issn=0962-9351}}</ref><ref name=":24">{{Cite journal | title = Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses | date = 2016-01-15|url=https://www.sciencedirect.com/science/article/pii/S0024320515301211|journal=Life Sciences|volume=145|pages=27–33 | last = Gugliandolo | first = Agnese | last2 = Gangemi | first2 = Chiara | last3 = Calabrò | first3 = Carlo | last4 = Vecchio | first4 = Mercurio | last5 = Di Mauro | first5 = Debora | last6 = Renis | first6 = Marcella | last7 = Ientile | first7 = Riccardo | last8 = Currò | first8 = Monica | last9 = Caccamo | first9 = Daniela|language=en|doi=10.1016/j.lfs.2015.12.028|issn=0024-3205}}</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name="ch1.4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">{{Cite journal | title = The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances | date = Jul 2011|url=https://www.mdpi.com/1660-4601/8/7/2770|journal=International Journal of Environmental Research and Public Health|volume=8|issue=7|pages=2770–2797 | last = De Luca | first = Chiara | authorlink = | last2 = Raskovic | first2 = Desanka | authorlink2 = | last3 = Pacifico | first3 = Valeria | authorlink3 = | last4 = Thai | first4 = Jeffrey Chung Sheun | authorlink4 = | last5 = Korkina | first5 = Liudmila | authorlink5 = |doi=10.3390/ijerph8072770|pmc=3155329|pmid=21845158|access-date=|issn=1660-4601|quote=|via=}}</ref><ref name="Caccamo2013">{{Cite journal | title = Xenobiotic sensor- and metabolism-related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population | date = 2013 |url=https://downloads.hindawi.com/journals/oximed/2013/831969.pdf | journal=Oxidative Medicine and Cellular Longevity|volume=2013|issue= | pages = 831969 | last = Caccamo | first = Daniela | authorlink = | last2 = Cesareo | first2 = Eleonora | authorlink2 = | last3 = Mariani | first3 = Serena | authorlink3 = | last4 = Raskovic | first4 = Desanka | authorlink4 = | last5 = Ientile | first5 = Riccardo | authorlink5 = | last6 = Currò | first6 = Monica | authorlink6 = | last7 = Korkina | first7 = Liudmila | last8 = De Luca | first8 = Chiara|doi=10.1155/2013/831969|pmc=3725911|pmid=23936614|access-date=|issn=1942-0994|quote=|via=}}</ref><ref name="Luca2014-metabolic">{{Cite journal | title = Metabolic and Genetic Screening of Electromagnetic Hypersensitive Subjects as a Feasible Tool for Diagnostics and Intervention | date = 2014-04-09|url=https://www.hindawi.com/journals/mi/2014/924184/|journal=Mediators of Inflammation|volume=2014|pages=e924184 | last = De Luca | first = Chiara | last2 = Chung Sheun Thai | first2 = Jeffrey | last3 = Raskovic | first3 = Desanka | last4 = Cesareo | first4 = Eleonora | last5 = Caccamo | first5 = Daniela | last6 = Trukhanov | first6 = Arseny | last7 = Korkina | first7 = Liudmila|language=en|doi=10.1155/2014/924184|issn=0962-9351}}</ref> including polymorphisms and differences in expression of the following: [[Cytochrome P450 2D6|CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref name="Attis2019">{{Cite web|url=https://www.karger.com/Article/FullText/497322 | title = Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity | last = D'Attis | first = S | authorlink = | last2 = Massari | first2 = S | authorlink2 = | date = 2019 | website = |pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14 | last3 = Mazzei | first3 = F | last4 = Maio | first4 = D | last5 = Bozzetti | first5 = MP | last6 = Vergallo | first6 = I | last7 = Mauro | first7 = S | last8 = Minelli | first8 = M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V|title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR|volume = 33|issue = 5 |pages = 971–8 |pmid = 15256524 |doi = 10.1093/ije/dyh251|journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251 | last = | first = | last2 = | first2 = | date = 2004|pmc=|quote= | last7 = | first7 = |via=}}</ref><ref name="Schnackenberget">{{Cite journal | last = Schnakenberg | first = Eckart | last2 = Fabig | first2 = Karl-Rainer | last3 = Stanulla | first3 = Martin | last4 = Strobl | first4 = Nils | last5 = Lustig | first5 = Michael | last6 = Fabig | first6 = Nathalie | last7 = Schloot | first7 = Werner | date = 2007-02-10 | title = A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1 | pages = 6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name="ch1.4" />
===COVID-19 and Long COVID===
There have been anecdotal reports of people with [[Long COVID]], or chronic COVID, developing new allergies, including fragrance and other chemical sensitivities.<ref name="Davis2021">{{Cite journal | last = Davis | first = Hannah | authorlink = Hannah Davis | last2 = Assaf | first2 = Gina | authorlink2 = Gina Assaf | last3 = McCorkell | first3 = Lisa | authorlink3 = | last4 = Wei | first4 = Hannah | authorlink4 = | last5 = Low | first5 = Ryan | authorlink5 = | last6 = Re’em | first6 = Yochai | authorlink6 = | last7 = Redfield | first7 = Signe | last8 = Austin | first8 = Jared | last9 = Akrami | first9 = Athena | date = 2020 | title=Characterizing Long COVID in an International Cohort: 7 Months of Symptoms and Their Impac|url=https://europepmc.org/article/PPR/PPR258069|journal=medRxiv|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/ | title = Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation | last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers | last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain | last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir | last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson | last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas | last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner | last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested | last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry | last9 =Joshi | first9 = Pradip | authorlink9 = Pradip Joshi | last10 = Powles | first10 = AC Peter | authorlink10 = A C Peter Powles | last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey | last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | pages = 7-115 | date = 2003 | pmid = | doi = 10.1300/J092v11n01_02 | url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf}}</ref><ref name="ICC2011primer">{{citation | last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers | last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande | last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir | last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas | last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick | last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell | last7 = Staines | first7 = D | authorlink7 = Donald Staines | last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles | last9 = Speight | first9 = N | authorlink9 = Nigel Speight | last10 = Vallings | first10 = R | authorlink10 = Rosamund Vallings | last11 = Bateman | first11 = L | authorlink11 = Lucinda Bateman | last12 = Bell | first12 = DS | authorlink12 = David Bell | last13 = Carlo-Stella | first13 = N | authorlink13 = Nicoletta Carlo-Stella | last14 = Chia | first14 = J | authorlink14 = John Chia | last15 = Darragh | first15 = A | authorlink15 = Austin Darragh | last16 = Gerken | first16 = A | authorlink16 = Anne Gerken | last17 = Jo | first17 = D | authorlink17 = Daehyun Jo | last18 = Lewis | first18 = DP | authorlink18 = Donald Lewis | last19 = Light | first19 = AR | authorlink19 = Alan Light | last20 = Light | first20 = KC | authorlink20 = Kathleen Light | last21 = Marshall-Gradisnik | first21 = S | authorlink21 = Sonya Marshall-Gradisnik | last22 = McLaren-Howard | first22 = J | authorlink22 = John McLaren-Howard | last23 = Mena | first23 = I | authorlink23 = Ismael Mena | last24 = Miwa | first24 = K | authorlink24 = Kunihisa Miwa | last25 = Murovska | first25 = M | authorlink25= Modra Murovska | last26 = Stevens | first26 = SR | authorlink26 = Staci Stevens | title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners | date = 2012| isbn = 978-0-9739335-3-6 | url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf }}</ref>
# The [[Canadian Consensus Criteria]] (2003) for ME/CFS lists "[[New allergies and intolerances|new sensitivities to food, medications and/or chemicals]]" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for Myalgic Encephalomyelitis lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# The U.S. ME/CFS Clinician Coalition publication '''Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) (2020)''' lists "chemical sensitivity" as a symptom of ME/CFS, and MCS as a comorbidity.<ref name="USMECFS-2020">{{Cite web | last = U.S. ME/CFS Clinician Coalition | date = Jul 2020 | url = https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view | title = Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms
== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the [[real illness|reality of the illness]].<ref name="Oreskes2011">{{Cite book | title = Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=| date = 2011 |publisher=Bloomsbury | last = Oreskes | first = Naomi | authorlink = | last2 = Conway | first2 = Erik M. | authorlink2 = |quote=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">{{Cite web|website=Deadline | first =
Erik | last = Pedersen | url =https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ | title = Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs" | date = Aug 17, 2019|quote=a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.}}</ref><ref name="Dusenberry">{{cite web | last = Dusenberry | first = Maya. |url=https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science | title = An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science|publisher=PS Mag | date = Sep 20, 2018|quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers-including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care... and add to the stigma and social isolation of an already profoundly marginalized group of people.'}}</ref><ref name="wp-talk">{{Cite web | title = Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref name="WP-cap">{{Cite web|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ | title = Wikipedia captured by skeptics|website=Skeptics about skeptics|access-date=Feb 12, 2020|quote=Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained.}}</ref><ref name="rampantharassment">{{Citation | url =http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ | title = Rampant Harassment on Wikipedia | last = Skeptical About Skeptics | first = | authorlink = | date = | website = Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation | last = Bundrant | first = Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog | date = Apr 15, 2015 |access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url = https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog | date = Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="Steinemann2018" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name="TaskForce2017" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref name="siege2013">{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege | date = Jun 26, 2013|quote="In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."}}</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last = Gale | first =Richard | last2 = Null | first2 = Gary | title = Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network | date = Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref name="Lees1998">{{citation | first = Paul R | last = Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog | date = Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last = Gavura | first = Scott | title = Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog | date = Jul 3, 2014}}</ref><ref name="LeesMold2002">{{citation|last =Lees-Haley|first =Paul R. | title=Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog | date = Dec 23, 2002}}</ref><ref name="Probe1999">{{citation | title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03 | date = Jan 1, 1999 | last = D.R.Z.}}</ref><ref name="Hall-Rea">{{citation | last = Hall | first = Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref name="MacBeth2018">{{citation|last =MacBeth | first = Braden|title = Afflicted and the Tragedy of Fake Illnesses | date = Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref name="BarrettQuestionable">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Questionable Organizations: An Overview | date = Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref name="BarrettVulberability">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Vulnerability to Quackery | date = Jan 16, 2019}}</ref><ref name="Barrett-AAEM">{{Citation | last = Barrett | first = Stephen | title = Regulatory Actions against AAEM Members|publisher=Quackwatch blog | date = Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref name="BarrettOilyphyria">{{Citation | last = Barrett | first = Stephen | title = The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog | date = Jan 22, 2010}}</ref><ref name="BarrettProclam">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = MCS Proclamations}}</ref><ref name="BarrettGWI-MCS">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | first2 = Ronald E | last2 = Gots | title = Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref name="BarrettFad">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Be Wary of "Fad" Diagnoses | date = Oct 6, 2018}}</ref><ref name="BarrettIndex">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis? | date = Mar 28, 2019}}</ref><ref name="BarrettCloseLook">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = A Close Look at "Multiple Chemical Sensitivity" | date = 1998}}</ref><ref name="resolution21">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity | date = Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Multiple Chemical Sensitivity: A Spurious Diagnosis | date = Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref name="CaseWP2009">{{citation | url =https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf | title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York | date = Nov 24, 2009}}</ref><ref name="WP-cap" /><ref name=":20">{{citation|last = Gale | first =Richard | title = Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url = http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network | date = Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref name="NcCarthyism">{{Cite web|url=https://prn.fm/stephen-barrett-medical-mccarthyism/ | title = Stephen Barrett and Medical McCarthyism|website=The Progressive Radio network blog|access-date= Feb 21, 2020}}</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name="ch1.4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref name="siege2013"/> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name="TaskForce2017" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name="Schwenk2004" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name="NICNAS" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name="Ch4.1-Noharm" /><ref name="VictorianHosp" /><ref name="NSW-factsheet" /><ref name="Mercy1999" /><ref name="Hosp2017" /><ref name="canberra2018" /><ref name="WA2019" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name="Aus-HR">{{citation | date = 2007 | title=Australian Human Rights Commission Access: Guidelines and information | last = Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation | last =Michaels | first = Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf | title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization | date = 2013 |quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>
==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ | title = "Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films | last = | first = | date = Nov 25, 2015 | website = YouTube | archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10 | title = Todd Haynes and Julianne Moore on Safe | last = | first = | date = |website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation | title = The 1995 film ‘Safe’ has new meaning during our coronavirus isolation | last = Di Corpo | first = Ryan | authorlink= | date = April 11, 2020 | website = |archive-url=|archive-date=|access-date = December 31, 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url = https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries | date = Sep 18, 2018}}</ref>
==Notable studies and publications==
*1987, Cullen, M.R. The worker with multiple chemical sensitivities: An overview<ref name="Cullen1987">{{Cite journal | title = The worker with multiple chemical sensitivities: an overview | date = Oct 1987|url=https://pubmed.ncbi.nlm.nih.gov/3313760/|journal=Occupational Medicine (Philadelphia, Pa.)|volume=2|issue=4 | pages = 655–661 | last = Cullen | first = M.R. | authorlink = |doi=|pmc=|pmid=3313760|access-date=|issn=0885-114X|quote=|via=}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/3313760 (Abstract)]

*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2005, Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref> - [https://www.sciencedirect.com/science/article/pii/S1438463905000210 (Abstract)]

*2014, Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity<ref name="Horowitz2014">{{Cite journal | title = Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity | date = Apr 2014|url=https://www.liebertpub.com/doi/pdf/10.1089/act.2014.20201|journal=Alternative and Complementary Therapies|volume=20|issue=2 | pages = 96–100 | last = Horowitz | first = Sala | authorlink = |doi=10.1089/act.2014.20201|pmc=|pmid=|access-date=|issn=1076-2809|quote=|via=}}</ref> [https://www.niehs.nih.gov/news/assets/docs_a_e/download_background_material_toxicantinduced_loss_of_tolerance_by_claudia_miller_508.pdf (Full text)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2016">{{Cite journal | last = | first = | authorlink = |vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al. | date = 2016-12-09 | title = Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives<ref name="Rossi2018" /> - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal | last = Viziano | first1 = A. | last2 = Micarelli | first2 = A. | last3 = Pasquantonio | first3 = G. | last4 = Della-Morte | first4 = D. | last5 = Alessandrini | first5 = M. | date = Nov 2018 | title = Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8 | pages = 923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]

*2019, International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products<ref name="Steinemann2019-international" /> - [https://link.springer.com/article/10.1007/s11869-019-00672-1 (Full text)]
*2021, Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity<ref name="Mazzatenta2021">{{Cite journal | title = Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity | date = 2021 | url=https://onlinelibrary.wiley.com/doi/abs/10.14814/phy2.15034|journal=Physiological Reports|volume=9|issue=18|pages=e15034 | last = Mazzatenta | first = Andrea | last2 = Pokorski | first2 = Mieczyslaw | last3 = Giulio | first3 = Camillo Di|language=en|doi=10.14814/phy2.15034|pmc=PMC8449310|pmid=34536058|issn=2051-817X}}</ref> - [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 (Full text)]
*2021, Mast cell activation may explain many cases of chemical intolerance<ref name="Miller2021">{{Cite journal | title = Mast cell activation may explain many cases of chemical intolerance | date = 2021-11-17|url=https://doi.org/10.1186/s12302-021-00570-3|journal=Environmental Sciences Europe|volume=33|issue=1|pages=129 | last = Miller | first = Claudia S. | last2 = Palmer | first2 = Raymond F. | last3 = Dempsey | first3 = Tania T. | last4 = Ashford | first4 = Nicholas A. | last5 = Afrin | first5 = Lawrence B.|language=en|doi=10.1186/s12302-021-00570-3|issn=2190-4715}}</ref> [https://link.springer.com/article/10.1186/s12302-021-00570-3 (Full text)]
*2021, Multiple Chemical Sensitivity<ref name="Zucco2021">{{Cite journal | title = Multiple Chemical Sensitivity | date = 2021-12-29|url=https://www.mdpi.com/2076-3425/12/1/46/htm|journal=Brain Sciences|volume=12|issue=1 | pages = 46 | last = Zucco | first = Gesualdo M. | last2 = Doty | first2 = Richard L.|doi=10.3390/brainsci12010046|issn=2076-3425}}</ref> [https://www.mdpi.com/2076-3425/12/1/46/htm (Full text)]

==News articles and interviews ==
*2017, [https://web.archive.org/web/20200215070226/https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world] - New Zealand Listener

*2018, [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condtion that affects one million Australia] - SBS television, Australia (Video)
*2019, [https://www.theguardian.com/lifeandstyle/2019/sep/15/fragrance-sensitivity-why-perfumed-products-can-cause-profound-health-problems Fragrance sensitivity: why perfumed products can cause profound health problems] - The Guardian

*2020, [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds] - Melbourne University Press
*2020, [https://i.stuff.co.nz/life-style/homed/kitchen/300272316/are-scented-cleaning-products-making-you-sick Are scented cleaning products making you sick?] - Stuff NZ
*2021, [https://www.washingtonpost.com/health/medical-mysteries/headache-chemical-smell-medical-mystery/2021/09/24/16c427ea-f2ec-11eb-a49b-d96f2dac0942_story.html The unusual headaches that upended this man's life began with a new car] - The Washington Post
*2021, [https://www.smh.com.au/national/experts-disturbed-over-toxic-discovery-in-popular-makeup-products-20210626-p584k2.html Experts ‘disturbed’ over toxic discovery in popular makeup products]<ref name="Whitehead2021">{{Cite journal | title = Fluorinated Compounds in North American Cosmetics | date = 2021-07-13|url=https://doi.org/10.1021/acs.estlett.1c00240|journal=Environmental Science & Technology Letters|volume=8|issue=7 | pages = 538–544 | last = Whitehead | first = Heather D. | last2 = Venier | first2 = Marta | last3 = Wu | first3 = Yan | last4 = Eastman | first4 = Emi | last5 = Urbanik | first5 = Shannon | last6 = Diamond | first6 = Miriam L. | last7 = Shalin | first7 = Anna | last8 = Schwartz-Narbonne | first8 = Heather | last9 = Bruton | first9 = Thomas A. | last10 = Blum | first10 = Arlene | last11 = Wang | first11 = Zhanyun|doi=10.1021/acs.estlett.1c00240}}</ref> - Sydney Morning Herald

== See also ==
* [[Toxicant-induced loss of tolerance (TILT)]]
* [[Mast cell activation syndrome]]
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[New allergies and intolerances]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf | title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome | last = Williams | first = Margaret | authorlink = Margaret Williams | date = Nov 10, 2010 | website = margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals
== References ==
{{reflist}}

[[Category:Allergy signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2024-05-21T00:04:20Z

Aletheia2020:Reordered, trying to put most useful content first. Removed some bits that were causing formatting problems (sorry but they were making the page hard to read). Fixed some language and deleted some less-important details. Trying to make page more accessible for general audience

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal | last = Rossi | first = Sabrina | authorlink = | last2 = Pitidis | first2 = Alessio | authorlink2 = | date = Feb 2018 | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{Cite book | url =|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|chapter-url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS | first = |location=Università degli Studi di Milano, Italy | date = 2019-05-23|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and [[mold]].<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="1.2-trigger">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>
==Signs and symptoms ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal| year = 1999 | title = Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /> and symptoms range from mild to severely disabling,<ref name="Ch1" /><ref name="NICNAS" /><ref name="TaskForce2017">{{Citation | last = Task Force on Environmental Health | date = 2017 | url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf | title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal | last = Steinemann | first = Anne | authorlink = | date = Mar 2018 | title = National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name="TaskForce2017" /><ref name="Loria2017">{{Cite journal | last = Loria-Kohen | first = Viviana | last2 = Marcos-Pasero | first2 = Helena | last3 = de la Iglesia | first3 = Rocío | last4 = Aguilar-Aguilar | first4 = Elena | last5 = Espinosa-Salinas | first5 = Isabel | last6 = Herranz | first6 = Jesús | last7 = Ramírez de Molina | first7 = Ana | last8 = Reglero | first8 = Guillermo | date = 2017-08-22 | title = Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref name="Gibson2016-unmet">{{Cite journal | last = Gibson | first = Pamela Reed | last2 = Leaf | first2 = Britney | last3 = Komisarcik | first3 = Victoria | date = 2016-01-12 | title = Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5 | pages = 75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref name="García2014">{{Cite journal | last = García-Sierra | first = Rosa | last2 = Álvarez-Moleiro | first2 = María | date = 2014-07-01 | title = Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2 | pages = 95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref name="Alobid2014">{{Cite journal | last = Alobid | first = Isam | last2 = Nogué | first2 = Santiago | last3 = Izquierdo-Dominguez | first3 = Adriana | last4 = Centellas | first4 = Silvia | last5 = Bernal-Sprekelsen | first5 = Manuel | last6 = Mullol | first6 = Joaquim | date = 2014-12-01 | title = Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal | last = Gibson | first = PR | author-link = | last2 = Vogel | first2 = VM | authorlink2 = | date = Jan 2009 | title = Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1 | pages = 72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Koch2006">{{Cite journal | last = Koch | first = Lynn | last2 = Vierstra | first2 = Courtney | last3 = Penix | first3 = Ken | date = 2006-09-01 | title = A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS can include [[headache]], [[migraine]], [[cognitive dysfunction|neurocognitive deficits]], [[dizziness]], [[fatigue]], [[arrhythmia|cardiac arrhythmia]], [[tachycardia]], [[hypotension]], [[hypertension]] (high blood pressure), [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], [[myalgia|muscle]] and [[Arthralgia|joint pain]], [[skin rash]]es, [[hives]], [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name="NICNAS" /><ref name="Valderrama2015" /><ref name="TaskForce2017" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal | last1 = Genuis | first1 = SJ | date = May 2013 | title = Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5 | pages = 572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291 | last2 = Ross | first2 = PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation. | last3 = Whysner | first3 = J | last4 = Covello | first4 = VT | last5 = Kuschner | first5 = M | last6 = Rifkind | first6 = AB | last7 = Sedler | first7 = MJ | last8 = Trichopoulos | first8 = D|via=}}</ref><ref name="Ross1999-Olfaction">{{cite journal|vauthors=Ross PM, Whysner J, Covello VT, Kuschner M, Rifkind AB, Sedler MJ, Trichopoulos D, Williams GM| year = 1999 | title = Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5 | pages = 467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN| year = 1999 | title = A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2 | pages = 73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book |isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp | title = A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs | date = 2010 | last=National Industrial Chemicals Notification and Assessment Scheme | last2 = Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" /> It can be associated with very high levels of disability. [[File:Cosmeticsbottles.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">{{Cite book | title = The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link= | url = |access-date= | date = 2017 | publisher=The text publishing company | last = Grenville | first = Kate | authorlink = |others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne, Australia | editor-last = | editor-first = |editor1-link=|editor-last2 = |editor-first2 = }}</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation |url = https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf | title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety | date = 2009|location=United States | page = 9}}</ref>]]
=== Chemicals that trigger symptoms ===
The following substances are common triggers for adverse symptoms people with MCS:
* [[pesticide]]s (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic [[fragrance]]s and products containing fragrance (eg. fragranced deodorant)
* laundry [[detergent]]s and fabric softeners
* [[cigarette smoke]] and woodfire smoke
* [[petrochemical|petrochemical solvents]] and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some [[medication intolerance|medications]] and anesthetics
* [[air pollution]] (eg. [[black carbon]], [[nitrogen oxide]], [[ozone]])
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name="NICNAS" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15">{{Cite book | title = [[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]] | last = Pall | first = Martin L. | authorlink = Martin Pall|publisher=Routledge & Harrington Park Press | date = 2007 | isbn=978-0789023896|location=New York}}</ref><ref name="Valderrama2015">{{Cite book | last = Valderrama Rodríguez | first = M | last2 = Revilla López | first2 = MC | last3 = Blas Diez | first3 = MP | last4 = Vázquez Fernández del Pozo | first4 = S | last5 = Martín Sánchez | first5 = Jl | title = Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS) | date = 2015 | trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name="Ziem2018">{{Cite journal | last = Ziem | first = Grace E. | authorlink = | date = 2018-04-24 | title = Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Pigatto2019" />

==Diagnosis and diagnostic criteria ==
Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name="NICNAS" /><ref name="TaskForce2017" />

===International Consensus Criteria 1999===
The 1999 international consensus on MCS is the most commonly used diagnostic criteria for MCS. The consensus is based on the Cullen criteria plus a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /><ref name="pmid10444033" /> MCS is defined as:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book | title = Psychiatry: An evidence-based text | pages = 793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date= | date = 2009-11-27|publisher=CRC Press | last = Hooper | first = Malcolm | authorlink = Malcolm Hooper|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location= | editor-last = Puri | editor-first = Bassant|editor1-link=|editor-last2 = Treasaden|editor-first2 = Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
===Lacour criteria 2005===
# symptom duration of at least 6 months
# symptoms in response to at least 2 of 11 categories of chemical exposures
# at least one [[central nervous system]] symptom is present (eg [[fatigue]], [[headache]]s or [[cognitive dysfunction|neurocognitive deficits]], and one symptom from another organ system
# symptoms causing adjustments of personal lifestyle, or of social or occupational life
# symptoms occurring when exposed and improving or resolving when exposures are removed
# symptoms are triggered by exposure levels that do not induce symptoms in other individuals who are exposed to the same levels<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref><ref name="Tran2013">{{Cite journal | last = Tran | first = Marie Thi Dao | first2 = Lars | last2 = Arendt-Nielsen | first3 = Ron | last3 = Kupers | first4 = Jesper | last4 = Elberling | title = Multiple chemical sensitivity: On the scent of central sensitization|journal=International journal of hygiene and environmental health|volume=216|issue=2|pages=202-210 | date = April 2013|pmid=22487274|url=http://www.bcwomens.ca/Specialized-Services-Site/Documents/Complex%20Chronic%20Diseases%20(CCDP)/Multiple%20Chemical%20Sensitivity%20(journal%20article).pdf | doi=10.1016/j.ijheh.2012.02.010|pmc=|quote=|access-date=|via=}}</ref><ref name="Damiami2021" />
===Diagnostic tools===
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />
===Differential diagnosis ===
A series of tests are needed to identify other potential causes of the symptoms. Particularly important to rule out are:
*[[Porphyria]]s
*[[Mastocytosis]] including systematic mastocytosis<ref name="Damiami2021">{{Cite journal | title = Italian Expert Consensus on Clinical and Therapeutic Management of Multiple Chemical Sensitivity (MCS) | date = 2021-10-27|url=https://doi.org/10.3390/ijerph182111294|journal=International Journal of Environmental Research and Public Health|volume=18|issue=21|pages=11294 | last = Damiani | first = Giovanni | last2 = Alessandrini | first2 = Marco | last3 = Caccamo | first3 = Daniela | last4 = Cormano | first4 = Andrea | last5 = Guzzi | first5 = Gianpaolo | last6 = Mazzatenta | first6 = Andrea | last7 = Micarelli | first7 = Alessandro | last8 = Migliore | first8 = Alberto | last9 = Piroli | first9 = Alba | last10 = Bianca | first10 = Margherita | last11 = Tapparo | first11 = Ottaviano|doi=10.3390/ijerph182111294|pmc=PMC8582949|pmid=34769816|issn=1660-4601}}</ref>

==Prevalence==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" />]] While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="NICNAS" /> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="TaskForce2017" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC | date = May 2004 | title = Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5 | pages = 746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Bloch2007">{{Cite journal | last = Bloch | first = Richard M. | last2 = Meggs | first2 = William J. | date = 2007-01-01 | title = Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression | url =https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref name="Berg2008">{{Cite journal | last = Berg | first = Nikolaj Drimer | last2 = Linneberg | first2 = Allan | last3 = Dirksen | first3 = Asger | last4 = Elberling | first4 = Jesper | date = 2008-07-01 | title = Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population | url =https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7 | pages = 881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref name="Andersson2008">{{Cite journal | last = Andersson | first = Linus | last2 = Johansson | first2 = Åke | last3 = Millqvist | first3 = Eva | last4 = Nordin | first4 = Steven | last5 = Bende | first5 = Mats | date = 2008-10-01 | title = Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5 | pages = 690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}<ref name="Gibson2016-MH">{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM | date = Apr 6, 2016 | title = Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf | journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Rossi2018" />

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305 | last = Steinemann | first = AC | title = A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health | date = 2005|volume=59|issue=6|pages=300-5}}</ref><ref name="Caress2009">{{Cite journal | last = Caress | first = SM | last2 = Steinemann | first2 = AC | date = 2009-02-01 | title = Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1 | pages = 71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade. They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Steinemann2018" />

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/ | title = Danimarca: nuovo codice per la MCS | last = | first = | authorlink = | date = 2014-10-14 | website = Infoamica|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14|url-status=}}</ref><ref name="Elberling2014-code">{{Cite journal | title = Patienter med symptomer, der er relateret til dufte og kemiske stoffer, kan nu kodes specifikt med Sundhedsvæsenets Klassifikationssystem | date = 2014-05-26|url=https://pubmed.ncbi.nlm.nih.gov/25096843/|journal=Ugeskrift for Laeger|volume=176|issue=11|pages=V10120627 | last = Elberling | first = Jesper | authorlink = | last2 = Bonde | first2 = Jens Peter Ellekilde | authorlink2 = | last3 = Vesterhauge | first3 = Søren | authorlink3 = | last4 = Bang | first4 = Søren | authorlink4 = | last5 = Linneberg | first5 = Allan | authorlink5 = | last6 = Zachariae | first6 = Claus | authorlink6 = | last7 = Johansen | first7 = Jeanne Duus | last8 = Blands | first8 = Jette | last9 = Skovbjerg | first9 = Sine|language=da|doi=|pmc=|pmid=25096843|access-date=|trans-title=A new classification code is available in the Danish health-care classification system for patients with symptoms related to chemicals and scents|issn=1603-6824|quote=|via=}}</ref>

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name="TaskForce2017" />{{Rp|37}}<ref name="CCHS2014">Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

While a 2018 study at the University of Melbourne found that 1 million Australians (6.5% of adults) reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name="Pigatto2019">{{Cite journal | last = Pigatto | first = Paolo D. | last2 = Guzzi | first2 = Gianpaolo | date = 2019-06-01 | title = Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name="Steinemann2018-Aus">{{Cite journal |url=https://www.sciencedirect.com/science/article/pii/S2211335518300457 | last = Steinemann | first = A. | title=Prevalence and effects of multiple chemical sensitivities in Australia|journal=Prev Med Rep | date = 2018 | volume=10|pages=191-4|issue=|doi=10.1016/j.pmedr.2018.03.007|pmc=PMC5984225|pmid=29868366|quote=|access-date=|via=}}</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name="Steinemann2018" /><ref name="Steinemann2018-Aus" />
== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name="Schwenk2004" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name="Schwenk2004" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref name="ICD10-GM">{{Cite book | title = ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&dq=%C3%9Cberempfindlichkeit%20T78.4&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4&f=false|access-date=| date = 2011 |publisher=Deutscher Ärzteverlag | last = World Health Organization | first = | authorlink = World Health Organization | last2 = DIMDI | first2 = | authorlink2 = |veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name="Ch4.1-Noharm" /><ref name="NICNAS" /> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" /> In 2012, Denmark introduced code '''DR688A1''' for ''Symptoms related to chemicals and scents'' (Symptomer relateret til dufte og kemiske stoffer fra SKS), in the [[Medically unexplained physical symptoms|Medically Unexplained Symptoms]], under ''R68.8 Other specified general symptoms and signs''.<ref name="Elberling2014-code" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html | title = Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) | last = Centers for Disease Control | first = | authorlink = Centers for Disease Control and Prevention | date = 2019-11-19 | website = [[Centers for Disease Control and Prevention]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

==Treatment==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name="TaskForce2017" /><ref name="Ch4.1-Noharm">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name="NICNAS" /><ref name="TaskForce2017" /><ref name="Valderrama2015" /><ref name="Ziem2018" /><ref name="Ch4.1-Noharm" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name="NICNAS" /><ref name="Gibson2003">{{cite journal | last = Gibson | first = PR | last2 = Elms | first2 = AN | last3 =Ruding | first3 = LA | date = 2003 | title = Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name="Ch4.1-Noharm" />

There is evidence that some patients with MCS might have [[hypoxia|poor tissue oxygenation]] when exposed to triggers,<ref name="Ch4.5">{{Cite book |chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> perhaps because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal | last = Horvath | first = I. | last2 = Loukides | first2 = S. | last3 = Wodehouse | first3 = T. | last4 = Kharitonov | first4 = S.A. | last5 = Cole | first5 = P.J. | last6 = Barnes | first6 = P.J. | date = 1998-10-01 | title = Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10 | pages = 867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref name="Ewing1993">{{Cite journal | last = Ewing | first = James F. | last2 = Maines | first2 = Mahin D. | date = 1993 | title = Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain | url =https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref name="Gregersen">{{Cite journal | last = Gregersen | first = Per | last2 = Klausen | first2 = Hans | last3 = Elsnab | first3 = Charlotte Uldal | date = 1987 | title = Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up | url =https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures helps some people.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book |trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were:
* face masks (with HEPA and VOC filters)
* portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters), and
* water purifiers.<ref name="Ch4.2" />

== Accessibility needs==
People with MCS typically experience significant access barriers to society and accessing services. They are also commonly subject to stigma and lack of understanding, perhaps because the condition is poorly understood. Nevertheless, it is recognised as a disability. For example, "a growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR" />

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name="TaskForce2017" /><ref name="Grenvillebook" /><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/ | title = Guidelines on the Use of Perfumes and Scented Products | last = | first = | authorlink = | date = | website = University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Steinemann2018-Aus" /><ref name="Flegel2015">{{Cite journal | last = Flegel | first = Ken | last2 = Martin | first2 = James G. | date = 2015-11-03 | title = Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name="stJosephs" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref name="notsosexy">{{Cite web |at=Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern | url =https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf | title=Not so sexy. The health risks of secret ingredients in fragrance | last = The campaign for safe cosmetics|publisher=The Environmental Working Group | date = 2010}}</ref><ref name="Steinemann2019-asthma">{{Cite journal | last = Steinemann | first = Anne | last2 = Goodman | first2 = Nigel | date = 2019-06-01 | title = Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6 | pages = 643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref name="Steinemann2019-international">{{Cite journal | title = International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products | date = 2019-05-01|url=https://doi.org/10.1007/s11869-019-00672-1|journal=Air Quality, Atmosphere & Health|volume=12|issue=5 | pages = 519–527 | last = Steinemann | first = Anne|language=en|doi=10.1007/s11869-019-00672-1|issn=1873-9326}}</ref><ref name="Nazaroff2004">[https://www.sciencedirect.com/science/article/abs/pii/S1352231004002171 Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865]</ref><ref name="Kumar1995">[https://pubmed.ncbi.nlm.nih.gov/7583865 Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433]</ref><ref name="Elberling2004">[https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2133.2004.06251.x?sid=nlm%3Apubmed Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203.]</ref><ref name="Elberling2009">[https://www.sciencedirect.com/science/article/abs/pii/S1438463909000728?via%3Dihub Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.]</ref><ref name="Mendell2007">[https://onlinelibrary.wiley.com/doi/10.1111/j.1600-0668.2007.00478.x Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.]</ref><ref name="Schnuch2010">[https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2133.2009.09510.x Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.]</ref><ref name="Neuenschwander2010">[https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/cssc.200900228 Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.]</ref><ref name="Nielsen2010">[https://pubmed.ncbi.nlm.nih.gov/15910405/ Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.]</ref><ref name="Nielsen2002">[https://pubmed.ncbi.nlm.nih.gov/12122569/ Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.]</ref><ref name="Venkatachari2008">[https://pubmed.ncbi.nlm.nih.gov/18688467/ Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.]</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref name="mcs-cv19-quebec">{{Cite web | last = The Environmental Health Association of Quebec | date = 2020 | url=https://aseq-ehaq.ca/en/projects/mcs-covid-19/ | title = Impacts of Covid-19 Health measures on people with multiple chemical sensitivities}}</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Steinemann2018-Aus" /><ref name="Grenvillebook" /><ref name="TaskForce2017" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name="stJosephs">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref name="ch5">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf | chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS | title = [The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS] | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23 | first = | authorlink = |volume=|pages=|edition=|isbn=}}</ref><ref name="Mercy1999">{{Cite web|url=http://www.lassentech.com/eimcspro.html | title = Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol | date = Sep 1999|publisher=Mercy Medical Centers New York and California}}</ref><ref name="Fisher2008">[https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.]</ref><ref name="Rea-surgerych">{{Cite book | last = Rea | first = William J. | authorlink = William Rea | date = 1996 | chapter=41 Surgery in the chemically sensitive|volume=IV | title = Chemical Sensitivity Tools of Diagnosis and Methods of Treatment|chapter-url=https://books.google.co.uk/books?id=cbsL8cUnO_EC&lpg=PA2015&pg=PA2803#v=onepage&q&f=true|url=https://books.google.com/books/about/Chemical_Sensitivity.html?id=cbsL8cUnO_EC | editor-last = Environmental Health Center|location=Dallas, Texas|publisher=CRC Press|pages=2803-2850|isbn=0873719654}}</ref><ref name="VictorianHosp">{{citation |url = https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals | title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals | date = Aug 25, 2011|website =Victoria Department of Health}}</ref><ref name="canberra2018">{{Cite web|url = http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx | title = Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities | date = 2018 | last = ACT Department of Health|access-date= | website = | first = Canberra, Australia | authorlink=|archive-url=|archive-date=}}</ref><ref name="NSW-factsheet">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx | title = Fact sheet: Multiple Chemical Sensitivity Disorder | last = NSW Health | first = | authorlink = | date = Sep 2, 2015 | website = NSW Health|archive-url=|archive-date=|access-date=2020-05-14}}</ref><ref name="Hosp2017">{{Cite web | last = Australian Commission on Safety and Quality in Health Care | date = 2017 | url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf | title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name="SA2016">{{Cite web|url = https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf | title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline | date = Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name="WA2019">{{Cite web |url=http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf | title=Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline | date = Sep 14, 2010|publisher=Western Australia Country Health Service.}}</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name="canberra2018" /><ref name="VictorianHosp" /><ref name="WA2019" /><ref name="SA2016" /> As well, some individual hospitals have their own policies for MCS patients.<ref name="Mercy1999" /><ref name="QHC2010">[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== Housing ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref name="amputated-lives">{{Cite book |chapter=The Elusive Search for a Place to Live | title = Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st|volume=|language=|title-link=|chapter-url=http://www.chemicalsensitivityfoundation.org/pdf/amputated-lives-ch2.pdf | url=|access-date= | date = November 20, 2008|publisher=Cumberland Press | last = Johnson | first =Alison | authorlink = |others=|doi=|oclc=|quote=|location=Parramatta, Australia}}</ref><ref name="Homelessness2002" /><ref name="ANRESS-2020">{{citation | title=Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy | date = Sep 2020 | first = Sharyn | last = Martin|pages=2}}</ref><ref name="Gibson2016" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name="ActionPlan2018">{{Cite web |url = https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf | title=An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)|publisher=Final Report of the Task Force on Environmental Health|location=Ottawa, Canada | date = Dec 2018}}</ref>{{Rp|12}}

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name="Homelessness2002">{{Citation | last = Environmental Health Coalition | first = | authorlink = | date = March 11, 2002 | title = Homelessness at critical level for Western Massachusetts chemically injured|publisher=Western Massachusetts|pages=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name="ANRESS-2020" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name="Gibson2016">{{Cite journal | last = Gibson | first = Pamela | authorlink =
| date = 2016-01-01 | title = A Review of the Life Impacts of Environmental Sensitivities | url = |journal=Internal Medicine Review|volume=|issue=May | page = 9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* [[mold illness|mold]]
* carpet
* fumes from paint
* [[pesticide]] residue
* fumes from [nearby] laundry facilities
* fumes from cleaning products in common areas and
* [[cigarette smoke]].<ref name=":3" />
People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name="ActionPlan2018" /> The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.<ref name="ActionPlan2018" /> It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.”<ref name="ActionPlan2018" />{{Rp|7,12,19}}

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name="NICNAS" /><ref name="Schwenk2004">{{Cite journal | last = Schwenk | first = Michael | date = 2004 | title = Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name="NICNAS" /><ref name="Schwenk2004" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name="Schwenk2004" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

==Possible causes==
[[File:MCS-IEI-biomarker-VOCs.png|thumb|'''MCS patients versus controls: VOCs in breath'''<br>
Basal exhaled VOCs data for MCS and controls, acquired with the ORT-VOC, are shown in a density plot.<br>
Source: Mazzatenta et al. (2021). [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 Physiological Reports, 9, e15034].<ref name="Mazzatenta2021" />]]
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name="TaskForce2017" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name="TaskForce2017" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name="ch1.4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018">{{citation | url =https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22 | title = Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport | date = Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or divide.

In 2021, a small study by Mazzatenta and colleagues found breath analysis of key [[volatile organic compound]]s (VOCs) differed between MCS patients and healthy controls, raising the possibility that breath analysis may be able to diagnose MCS in future. Breath analysis can already be used to aid diagnosis for some illnesses.<ref name="Mazzatenta2021" />

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

The [[Toxicant-induced loss of tolerance (TILT)|Toxicant-Induced Loss of Tolerance]] (TILT) hypothesis proposed by Miller (1996) uses the name TILT for multiple chemical sensitivity, and describes a two-phase process. First, there is ''either'' a single major exposure to chemicals ''or'' many smaller exposures, which then result in chemical intolerance or ''sensitization''. In the second phase, low or very low levels of exposure to chemicals cause symptoms that did not occur before sensitization.<ref name="Horowitz2014" /> According to the TILT hypothesis, [[Food intolerance|food and medication intolerances]] frequently occur along with chemical sensitivity. Miller (2021) believes that [[Mast cell activation syndrome|Mast Cell Activation Syndrome]] may account for TILT/MCS.<ref name="Miller2021" />

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name="1.2-trigger" /><ref name="NICNAS" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name="ch1.4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15" /><ref name="Pall2011">{{Cite journal | last = Pall | first = Martin L. | authorlink = Martin Pall | last2 = Satterlee | first2 = JD | date = 2001 | title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder |url = https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of [[limbic kindling]], neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="NICNAS" />

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name="ch1.4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name="Bell1999">{{Cite journal | last = Bell | first = Iris R. | last2 = Baldwin | first2 = Carol M. | last3 = Fernandez | first3 = Mercedes | last4 = Schwartz | first4 = Gary E.R. | date = 1999-04-01 | title = Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name="Bell-kindling">{{Cite journal | last = Bell | first = IR | author-link = | last2 = Rossi | first2 = J | authorlink2 = | last3 = Gilbert | first3 = ME | authorlink3 = | last4 = Kobal | first4 = G | authorlink4 = | last5 = Morrow | first5 = LA | authorlink5 = | last6 = Newlin | first6 = DB | authorlink6 = | last7 = Sorg | first7 = BA | last8 = Wood | first8 = RW | date = 1997-03-01 | title = Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs' theory of neurogenic inflammation.<ref name="Meggs2017">{{Cite journal | last = Meggs | first = William J. | date = 2017-05-09 | title = The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2 | pages = 83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name="ch1.4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk | url =https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref name="Reid2001">{{cite journal | title = Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6 | pages = 604–9|doi=10.1093/aje/153.6.604|pmid=11257069 | last = Reid | first = S | last2 = Hotopf | first2 = M | authorlink2 = Matthew Hotopf | last3 = Hull | first3 = L | last4 = Ismail | first4 = K | last5 = Unwin | first5 = C | last6 = Wessely | first6 = S | authorlink6 = Simon Wessely | date = 2001 | pmc=|quote=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref name="Gronseth2005">{{Cite journal | title = Gulf war syndrome: a toxic exposure? A systematic review | date = 2005-05-01|url=https://doi.org/10.1016/j.ncl.2004.12.011|journal=Neurologic clinics|volume=23|issue=2 | pages = 523–540 | last = Gronseth | first = Gary S|doi=10.1016/j.ncl.2004.12.011|pmid=15757795|issn=1557-9875}}</ref><ref name="VA2014">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf | title=Clinical practice guideline for the management of chronic multisystem illness | last = U.S. Department of Veterans Affairs, Department of Defense | date = Oct 2014}}</ref><ref name="Spelman2012">{{Cite journal | last = Spelman | first = Juliette F. | last2 = Hunt | first2 = Stephen C. | last3 = Seal | first3 = Karen H. | last4 = Burgo-Black | first4 = A. Lucile | date = 2012-09-01 | title = Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name="VA2014" />

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal | last = Rea | first = William J. | date = 2018-06-01 | title = A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin | url =http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6 | pages = 889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref name="Lieberman2006">{{Cite journal | last = Lieberman | first = Allan | last2 = Rea | first2 = William | last3 = Curtis | first3 = Luke | date = 2006-09-01 | title = Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3 | pages = 763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref name="Vojdani2003">{{Cite journal | last = Vojdani | first = Aristo | last2 = Thrasher | first2 = Jack D. | last3 = Madison | first3 = Roberta A. | last4 = Gray | first4 = Michael R. | last5 = Heuser | first5 = Gunnar | last6 = Campbell | first6 = Andrew W. | date = 2003-07-01 | title = Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7 | pages = 421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref name="WHO-Indoor2011">{{Cite book | last = Hänninen | first = Otto O. | authorlink = | date = 2001 | editor-last = Adan | editor-first = Olaf C. G. |editor2-last=Samson| editor2-first = Robert A. | title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal | last = Knibbs | first = Luke D. | authorlink = | last2 = Woldeyohannes | first2 = Solomon | authorlink2 = | last3 = Marks | first3 = Guy B. | authorlink3 = | last4 = Cowie | first4 = Christine T. | authorlink4 = | date = 2018 | title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref name="Quansah2012">{{Cite journal | last = Quansah | first = Reginald | last2 = Jaakkola | first2 = Maritta S. | last3 = Hugg | first3 = Timo T. | last4 = Heikkinen | first4 = Sirpa A M. | last5 = Jaakkola | first5 = Jouni J.K. | date = 2012-11-07 | title = Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref name="Mendell2011">{{Cite journal | last = Mendell | first = Mark J | author-link = | last2 = Mirer | first2 = Anna G | authorlink2 = | last3 = Cheung | first3 = Kerry | authorlink3 = | last4 = Tong | first4 = My | authorlink4 = | last5 = Douwes | first5 = Jeroen | authorlink5 = | date = 2011-06-01 | title = Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6 | pages = 748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "[[dizziness]], [[seizure]]s, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name="Bell1999" /><ref name="Bell-kindling" /><ref name="Meggs2017" /><ref name="Tran2013" />

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name="Meggs2017" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name="ch1.4" /><ref name="Bell1994">{{Cite journal | title = EEG responses to low-level chemicals in normals and cacosmics | date = 1994-07-01|url=https://europepmc.org/article/med/7778120|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 633–643 | last = Schwartz | first = G E | last2 = Bell | first2 = I R | last3 = Dikman | first3 = Z V | last4 = Fernandez | first4 = M | last5 = Kline | first5 = JP | last6 = Peterson | first6 = JM | last7 = Wright | first7 = KP | pmid=7778120|issn=1477-0393}}</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref name="Bell1998">{{Cite journal | title = Differential Resting Quantitative Electroencephalographic Alpha Patterns in Women with Environmental Chemical Intolerance, Depressives, and Normals | date = 1998-03-01|url=https://www.sciencedirect.com/science/article/pii/S000632239700245X|journal=Biological Psychiatry|volume=43|issue=5|pages=376–388 | last = Bell | first = Iris R | last2 = Schwartz | first2 = Gary E | last3 = Hardin | first3 = Elizabeth E | last4 = Baldwin | first4 = Carol M | last5 = Kline | first5 = John P|language=en|doi=10.1016/S0006-3223(97)00245-X|issn=0006-3223}}</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name="ch1.4" /><ref name="Callender1994">{{Cite journal | title = Evaluation of chronic neurological sequelae after acute pesticide exposure using spect brain scans | date = 1994-03-01|url=https://doi.org/10.1080/15287399409531843|journal=Journal of Toxicology and Environmental Health|volume=41|issue=3|pages=275–284 | last = Callender | first = Thomas James | last2 = Morrow | first2 = Lisa | last3 = Subramanian | first3 = Kodanallur|doi=10.1080/15287399409531843|pmid=8126750|issn=0098-4108}}</ref><ref name="Callender1993">{{Cite book | title = Neurobehavioral Methods and Effects in Occupational and Environmental Health|chapter=Three-Dimensional Brain Metabolic Imaging in Patients with Toxic Encephalopathy. Presented at the Fourth International Symposium on Neurobehavioral Methods and Effects in Occupational and Environmental Health, July 8–11, 1991, Tokyo, Japan. | date = 1994-01-01|url=https://www.sciencedirect.com/science/article/pii/B9780120597857500478 | pages = 451–475 | last = Callender | first = Thomas J. | authorlink = | last2 = Morrow | first2 = Lisa | authorlink2 = | last3 = Subramanian | first3 = Kodanallur | authorlink3 = | last4 = Duhon | first4 = Dan | authorlink4 = | last5 = Ristovv | first5 = Mona | authorlink5 = |isbn=978-0-12-059785-7|language=en|publisher=Academic Press | editor-last = Araki|editor-first = Shunichi|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name="Heuser1994">{{Cite journal | title = NeuroSPECT findings in patients exposed to neurotoxic chemicals | date = 1994-07-01|url=https://europepmc.org/article/med/7778114|journal=Toxicology and industrial health|volume=10|issue=4-5 | pages = 561–571 | last = Heuser | first = G | last2 = Mena | first2 = I | last3 = Alamos | first3 = F|pmid=7778114|issn=1477-0393}}</ref><ref name="Hillert2007">{{Cite journal | title = Odor processing in multiple chemical sensitivity | date = 2007 | url=https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266|journal=Human Brain Mapping|volume=28|issue=3|pages=172–182 | last = Hillert | first = Lena | last2 = Musabasic | first2 = Vildana | last3 = Berglund | first3 = Hans | last4 = Ciumas | first4 = Carolina | last5 = Savic | first5 = Ivanka|language=en|doi=10.1002/hbm.20266|pmc=PMC6871299|pmid=16767766|issn=1097-0193}}</ref><ref name="Ross1999-neurotoxic">{{Cite journal | title = Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities† | date = 1999-04-01|url=https://doi.org/10.1177/074823379901500316|journal=Toxicology and Industrial Health|volume=15|issue=3-4 | pages = 415–420 | last = Ross | first = Gerald H. | last2 = Rea | first2 = William J. | last3 = Johnson | first3 = Alfred R. | last4 = Hickey | first4 = David C. | last5 = Simon | first5 = Theodore R.|language=en|doi=10.1177/074823379901500316|issn=0748-2337}}</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name="ch1.4" /><ref name="Alessandrini2016">{{Cite journal | title = Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity | date = 2016-03-01|url=https://doi.org/10.1007/s10548-015-0453-3|journal=Brain Topography|volume=29|issue=2|pages=243–252 | last = Alessandrini | first = Marco | last2 = Micarelli | first2 = Alessandro | last3 = Chiaravalloti | first3 = Agostino | last4 = Bruno | first4 = Ernesto | last5 = Danieli | first5 = Roberta | last6 = Pierantozzi | first6 = Mariangela | last7 = Genovesi | first7 = Giuseppe | last8 = Öberg | first8 = Johanna | last9 = Pagani | first9 = Marco | last10 = Schillaci | first10 = Orazio|language=en|doi=10.1007/s10548-015-0453-3|issn=1573-6792}}</ref><ref name="Chiaravalloti2015">{{Cite journal | title = Cortical activity during olfactory stimulation in multiple chemical sensitivity: a 18F-FDG PET/CT study | date = 2015-04-01|url=https://doi.org/10.1007/s00259-014-2969-2|journal=European Journal of Nuclear Medicine and Molecular Imaging|volume=42|issue=5 | pages = 733–740 | last = Chiaravalloti | first = Agostino | last2 = Pagani | first2 = Marco | last3 = Micarelli | first3 = Alessandro | last4 = Di Pietro | first4 = Barbara | last5 = Genovesi | first5 = Giuseppe | last6 = Alessandrini | first6 = Marco | last7 = Schillaci | first7 = Orazio|language=en|doi=10.1007/s00259-014-2969-2|issn=1619-7089}}</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018" />{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name="ch1.4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref name="Albright1992">{{Cite journal | title = Is There Evidence of an Immunologic Basis for Multiple Chemical Sensitivity? | date = Sep 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800420|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=215–219 | last = Albright | first = Joseph F. | authorlink = | last2 = Goldstein | first2 = Robert A. | authorlink2 = |doi=10.1177/074823379200800420|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref><ref name="Meggs1992">{{Cite journal | title = Multiple Chemical Sensitivities and the Immune System | date = Jul 1992|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800419|journal=Toxicology and Industrial Health|volume=8|issue=4|pages=203–214 | last = Meggs | first = William J. | authorlink = |doi=10.1177/074823379200800419|pmc=|pmid=|access-date=|issn=0748-2337|quote=|via=}}</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref name="Labarge2000">{{Cite journal | title = Multiple Chemical Sensitivity: A Review of the Theoretical and Research Literature | date = 2000-12-01|url=https://doi.org/10.1023/A:1026460726965|journal=Neuropsychology Review|volume=10|issue=4|pages=183–211 | last = Labarge | first = Andrew S. | last2 = McCaffrey | first2 = Robert J.|language=en|doi=10.1023/A:1026460726965|issn=1573-6660}}</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name="ch1.4" /><ref name="Belpomme2015">{{Cite journal | title = Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder | date = 2015-12-01|url=https://www.degruyter.com/document/doi/10.1515/reveh-2015-0027/html|journal=Reviews on Environmental Health|volume=30|issue=4|pages=251–271 | last = Belpomme | first = Dominique | last2 = Campagnac | first2 = Christine | last3 = Irigaray | first3 = Philippe|language=en|doi=10.1515/reveh-2015-0027|issn=2191-0308}}</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus. These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name="ch1.4" /><ref name="Belpomme2015" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref name="ch3.11">{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf | title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS | last = Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy | date = 2019-05-23}}</ref><ref name="Hrda2010">{{Cite journal | title = The role of environmental factors in autoimmune thyroiditis | date = 2010 | url=https://pubmed.ncbi.nlm.nih.gov/20588228/|journal=Neuro Endocrinology Letters|volume=31|issue=3|pages=283–289 | last = Hybenova | first = Monika | last2 = Hrda | first2 = Pavlina | last3 = Procházková | first3 = Jarmila | last4 = Stejskal | first4 = Vera | last5 = Sterzl | first5 = Ivan|pmid=20588228|issn=0172-780X}}</ref><ref name="Ziem1997">{{Cite journal | title = Profile of patients with chemical injury and sensitivity. | date = 1997-03-01|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417|journal=Environmental Health Perspectives|volume=105|issue=suppl 2 | pages = 417–436 | last = Ziem | first = G. | last2 = McTamney | first2 = J.|doi=10.1289/ehp.97105s2417|pmc=PMC1469804|pmid=9167975}}</ref><ref name="Nogue2007">{{Cite journal | title = Sensibilidad química múltiple: análisis de 52 casos | date = 2007-06-01|url=https://doi.org/10.1157/13107370|journal=Medicina clinica|volume=129|issue=3 | pages = 96–9 | last = Nogué | first = Santiago | authorlink = | last2 = Fernández-Solá | first2 = Joaquim | authorlink2 = | last3 = Rovira | first3 = Elisabet | authorlink3 = | last4 = Montori | first4 = Elisabet | authorlink4 = | last5 = Fernández-Huerta | first5 = José Manuel | authorlink5 = | last6 = Munné | first6 = Pere | authorlink6 = |language=es|doi=10.1157/13107370|pmc=|pmid=17594860|access-date=|trans-title=Multiple chemical sensitivity: study of 52 cases|issn=1578-8989|quote=|via=}}</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name="TaskForce2017" /><ref name="ch1.4" /><ref name="Genuis2013" /><ref name="Tuuminen2018">{{Cite journal | title = Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives | date = Aug 2018|url=https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=8|pages=e429 | last = Tuuminen | first = Tamara | authorlink = |language=en-US|doi=10.1097/JOM.0000000000001369|pmc=|pmid=|access-date=|issn=1076-2752|quote=|via=}}</ref><ref name="Davidoff1994">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Fogarty | first2 = L. | authorlink2 = | date = Sep 1994 | title = Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Bransfield2019">{{Cite journal | title = Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty | date = 2019-10-08|url=https://doi.org/10.3390/healthcare7040114|journal=Healthcare|volume=7|issue=4|pages=114 | last = Bransfield | last2 = Friedman|doi=10.3390/healthcare7040114|pmc=PMC6955780|pmid=31597359|issn=2227-9032}}</ref><ref name="Steinemann2018" /><ref name="Davidoff1996">{{Cite journal | last = Davidoff | first = A.L. | authorlink = | last2 = Keyl | first2 = P.M. | authorlink2 = | date = May 1996 | title = Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group | url =https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref name="Gots1995">{{Cite journal | last = Gots | first = Ronald E. | date = 1995-01-01 | title = Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref name="Hainge2003">{{citation | first =Kimberly | last = Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf | work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1 | date =Fall 2003 | title = Multiple chemical sensitivity|pages=3|edition=}}</ref>
# that nocebo responses may operate in MCS,<ref name="Binkley1997">{{Cite journal | last = Binkley | first = K | author-link = | last2 = Kutcher | first2 = S | authorlink2 = | date = Apr 1997 | title = Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4 | pages = 570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref name="Witthoft2008">[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref name="Bailer2005">{{Cite journal | title = Evidence for overlap between idiopathic environmental intolerance and somatoform disorders | date = Nov 2005|url=https://pubmed.ncbi.nlm.nih.gov/16314597|journal=Psychosomatic Medicine|volume=67|issue=6 | pages = 921–929 | last = Bailer | first = Josef | author-link = | last2 = Witthöft | first2 = Michael | authorlink2 = | last3 = Paul | first3 = Christine | authorlink3 = | last4 = Bayerl | first4 = Christiane | authorlink4 = | last5 = Rist | first5 = Fred | authorlink5 = |doi=10.1097/01.psy.0000174170.66109.b7|pmc=|pmid=16314597|access-date=|issn=1534-7796|quote=|via=}}</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name="ch1.4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name="ch1.4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name="ch1.4" /><ref name="Davidoff1994" /><ref name="Davidoff1996" />

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name="TaskForce2017" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref name="Gibson2011-doc">{{Cite journal | title = Physicians' perceptions and practices regarding patient reports of multiple chemical sensitivity | date = 2011 |url=https://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf | journal=ISRN nursing|volume=2011|issue= | pages = 838930 | last = Gibson | first = Pamela Reed | authorlink = | last2 = Lindberg | first2 = Amanda | authorlink2 = |doi=10.5402/2011/838930|pmc=3168894|pmid=22007328|access-date=|issn=2090-5491|quote=|via=}}</ref><ref name="Gibson2009" /><ref name="MCS-EI">{{Cite web | title = MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]|url-status=dead | url =https://www.counselingatcela.com/mcs-and-eis|archive-date = 2020-10-21|archive-url=https://web.archive.org/web/20201021235254/https://www.counselingatcela.com/mcs-and-eis|website=The Counseling Center at CELA|quote=Is MCS a mental illness? MCS is not a mental illness}}</ref><ref name="PMC2821254">{{Cite journal | last = Lavergne | first = M. Ruth | authorlink = | last2 = Cole | first2 = Donald C. | authorlink2 = | last3 = Kerr | first3 = Kathleen | authorlink3 = | last4 = Marshall | first4 = Lynn M. | authorlink4 = | date = Feb 2010 | title = Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal | last = Caress | first = Stanley M | authorlink = | last2 = Steinemann | first2 = Anne C | authorlink2 = | date = 2003-09-01 | title = A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref name="Brussels2015">''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of May 18, 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref name="nocebohh">{{citation |url = https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response | website = Harvard Health. Harvard Medical School blog | date = Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref name="Bittar2015">{{Cite journal | last = Bittar | first = Caroline | authorlink = | last2 = Nascimento | first2 = Osvaldo J.M. | authorlink2 = | date = Jan 2015 | title = Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1 | pages = 58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name="TaskForce2017" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref name="DSM-5">{{Cite book | title = Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|language=|title-link=|url= | date = May 15, 2014|publisher=American Psychiatric Press | last = American Psychiatric Association | first = | authorlink = |oclc=|quote=|archive-url=|archive-date=|location=Washington, D.C}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref name="icd10cm-f45.8">{{Citation | url =https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 | title = Other somatoform disorders {{!}} ICD-10-CM Diagnosis Code F45.8 | date = 2020 | website = ICD-10-CM}}</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name="TaskForce2017" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name="ch1.4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name="ch1.4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name="ch1.4" /><ref name=":23">{{Cite journal | title = Role of Polymorphisms of Inducible Nitric Oxide Synthase and Endothelial Nitric Oxide Synthase in Idiopathic Environmental Intolerances | date = 2015-03-24|url=https://www.hindawi.com/journals/mi/2015/245308/|journal=Mediators of Inflammation|volume=2015 |pages=e245308 | last = De Luca | first = Chiara | last2 = Gugliandolo | first2 = Agnese | last3 = Calabrò | first3 = Carlo | last4 = Currò | first4 = Monica | last5 = Ientile | first5 = Riccardo | last6 = Raskovic | first6 = Desanka | last7 = Korkina | first7 = Ludmila | last8 = Caccamo | first8 = Daniela|language=en|doi=10.1155/2015/245308|issn=0962-9351}}</ref><ref name=":24">{{Cite journal | title = Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses | date = 2016-01-15|url=https://www.sciencedirect.com/science/article/pii/S0024320515301211|journal=Life Sciences|volume=145|pages=27–33 | last = Gugliandolo | first = Agnese | last2 = Gangemi | first2 = Chiara | last3 = Calabrò | first3 = Carlo | last4 = Vecchio | first4 = Mercurio | last5 = Di Mauro | first5 = Debora | last6 = Renis | first6 = Marcella | last7 = Ientile | first7 = Riccardo | last8 = Currò | first8 = Monica | last9 = Caccamo | first9 = Daniela|language=en|doi=10.1016/j.lfs.2015.12.028|issn=0024-3205}}</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name="ch1.4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">{{Cite journal | title = The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances | date = Jul 2011|url=https://www.mdpi.com/1660-4601/8/7/2770|journal=International Journal of Environmental Research and Public Health|volume=8|issue=7|pages=2770–2797 | last = De Luca | first = Chiara | authorlink = | last2 = Raskovic | first2 = Desanka | authorlink2 = | last3 = Pacifico | first3 = Valeria | authorlink3 = | last4 = Thai | first4 = Jeffrey Chung Sheun | authorlink4 = | last5 = Korkina | first5 = Liudmila | authorlink5 = |doi=10.3390/ijerph8072770|pmc=3155329|pmid=21845158|access-date=|issn=1660-4601|quote=|via=}}</ref><ref name="Caccamo2013">{{Cite journal | title = Xenobiotic sensor- and metabolism-related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population | date = 2013 |url=https://downloads.hindawi.com/journals/oximed/2013/831969.pdf | journal=Oxidative Medicine and Cellular Longevity|volume=2013|issue= | pages = 831969 | last = Caccamo | first = Daniela | authorlink = | last2 = Cesareo | first2 = Eleonora | authorlink2 = | last3 = Mariani | first3 = Serena | authorlink3 = | last4 = Raskovic | first4 = Desanka | authorlink4 = | last5 = Ientile | first5 = Riccardo | authorlink5 = | last6 = Currò | first6 = Monica | authorlink6 = | last7 = Korkina | first7 = Liudmila | last8 = De Luca | first8 = Chiara|doi=10.1155/2013/831969|pmc=3725911|pmid=23936614|access-date=|issn=1942-0994|quote=|via=}}</ref><ref name="Luca2014-metabolic">{{Cite journal | title = Metabolic and Genetic Screening of Electromagnetic Hypersensitive Subjects as a Feasible Tool for Diagnostics and Intervention | date = 2014-04-09|url=https://www.hindawi.com/journals/mi/2014/924184/|journal=Mediators of Inflammation|volume=2014|pages=e924184 | last = De Luca | first = Chiara | last2 = Chung Sheun Thai | first2 = Jeffrey | last3 = Raskovic | first3 = Desanka | last4 = Cesareo | first4 = Eleonora | last5 = Caccamo | first5 = Daniela | last6 = Trukhanov | first6 = Arseny | last7 = Korkina | first7 = Liudmila|language=en|doi=10.1155/2014/924184|issn=0962-9351}}</ref> including polymorphisms and differences in expression of the following: [[Cytochrome P450 2D6|CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref name="Attis2019">{{Cite web|url=https://www.karger.com/Article/FullText/497322 | title = Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity | last = D'Attis | first = S | authorlink = | last2 = Massari | first2 = S | authorlink2 = | date = 2019 | website = |pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14 | last3 = Mazzei | first3 = F | last4 = Maio | first4 = D | last5 = Bozzetti | first5 = MP | last6 = Vergallo | first6 = I | last7 = Mauro | first7 = S | last8 = Minelli | first8 = M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V|title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR|volume = 33|issue = 5 |pages = 971–8 |pmid = 15256524 |doi = 10.1093/ije/dyh251|journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251 | last = | first = | last2 = | first2 = | date = 2004|pmc=|quote= | last7 = | first7 = |via=}}</ref><ref name="Schnackenberget">{{Cite journal | last = Schnakenberg | first = Eckart | last2 = Fabig | first2 = Karl-Rainer | last3 = Stanulla | first3 = Martin | last4 = Strobl | first4 = Nils | last5 = Lustig | first5 = Michael | last6 = Fabig | first6 = Nathalie | last7 = Schloot | first7 = Werner | date = 2007-02-10 | title = A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1 | pages = 6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name="ch1.4" />
===COVID-19 and Long COVID===
There have been anecdotal reports of people with [[Long COVID]], or chronic COVID, developing new allergies, including fragrance and other chemical sensitivities.<ref name="Davis2021">{{Cite journal | last = Davis | first = Hannah | authorlink = Hannah Davis | last2 = Assaf | first2 = Gina | authorlink2 = Gina Assaf | last3 = McCorkell | first3 = Lisa | authorlink3 = | last4 = Wei | first4 = Hannah | authorlink4 = | last5 = Low | first5 = Ryan | authorlink5 = | last6 = Re’em | first6 = Yochai | authorlink6 = | last7 = Redfield | first7 = Signe | last8 = Austin | first8 = Jared | last9 = Akrami | first9 = Athena | date = 2020 | title=Characterizing Long COVID in an International Cohort: 7 Months of Symptoms and Their Impac|url=https://europepmc.org/article/PPR/PPR258069|journal=medRxiv|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/ | title = Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation | last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers | last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain | last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir | last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson | last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas | last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner | last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested | last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry | last9 =Joshi | first9 = Pradip | authorlink9 = Pradip Joshi | last10 = Powles | first10 = AC Peter | authorlink10 = A C Peter Powles | last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey | last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | pages = 7-115 | date = 2003 | pmid = | doi = 10.1300/J092v11n01_02 | url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf}}</ref><ref name="ICC2011primer">{{citation | last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers | last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande | last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir | last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas | last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick | last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell | last7 = Staines | first7 = D | authorlink7 = Donald Staines | last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles | last9 = Speight | first9 = N | authorlink9 = Nigel Speight | last10 = Vallings | first10 = R | authorlink10 = Rosamund Vallings | last11 = Bateman | first11 = L | authorlink11 = Lucinda Bateman | last12 = Bell | first12 = DS | authorlink12 = David Bell | last13 = Carlo-Stella | first13 = N | authorlink13 = Nicoletta Carlo-Stella | last14 = Chia | first14 = J | authorlink14 = John Chia | last15 = Darragh | first15 = A | authorlink15 = Austin Darragh | last16 = Gerken | first16 = A | authorlink16 = Anne Gerken | last17 = Jo | first17 = D | authorlink17 = Daehyun Jo | last18 = Lewis | first18 = DP | authorlink18 = Donald Lewis | last19 = Light | first19 = AR | authorlink19 = Alan Light | last20 = Light | first20 = KC | authorlink20 = Kathleen Light | last21 = Marshall-Gradisnik | first21 = S | authorlink21 = Sonya Marshall-Gradisnik | last22 = McLaren-Howard | first22 = J | authorlink22 = John McLaren-Howard | last23 = Mena | first23 = I | authorlink23 = Ismael Mena | last24 = Miwa | first24 = K | authorlink24 = Kunihisa Miwa | last25 = Murovska | first25 = M | authorlink25= Modra Murovska | last26 = Stevens | first26 = SR | authorlink26 = Staci Stevens | title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners | date = 2012| isbn = 978-0-9739335-3-6 | url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf }}</ref>
# The [[Canadian Consensus Criteria]] (2003) for ME/CFS lists "[[New allergies and intolerances|new sensitivities to food, medications and/or chemicals]]" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for Myalgic Encephalomyelitis lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# The U.S. ME/CFS Clinician Coalition publication '''Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) (2020)''' lists "chemical sensitivity" as a symptom of ME/CFS, and MCS as a comorbidity.<ref name="USMECFS-2020">{{Cite web | last = U.S. ME/CFS Clinician Coalition | date = Jul 2020 | url = https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view | title = Diagnosing and Treating Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms
== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the [[real illness|reality of the illness]].<ref name="Oreskes2011">{{Cite book | title = Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=| date = 2011 |publisher=Bloomsbury | last = Oreskes | first = Naomi | authorlink = | last2 = Conway | first2 = Erik M. | authorlink2 = |quote=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">{{Cite web|website=Deadline | first =
Erik | last = Pedersen | url =https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ | title = Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs" | date = Aug 17, 2019|quote=a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.}}</ref><ref name="Dusenberry">{{cite web | last = Dusenberry | first = Maya. |url=https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science | title = An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science|publisher=PS Mag | date = Sep 20, 2018|quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers-including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care... and add to the stigma and social isolation of an already profoundly marginalized group of people.'}}</ref><ref name="wp-talk">{{Cite web | title = Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref name="WP-cap">{{Cite web|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ | title = Wikipedia captured by skeptics|website=Skeptics about skeptics|access-date=Feb 12, 2020|quote=Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained.}}</ref><ref name="rampantharassment">{{Citation | url =http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/ | title = Rampant Harassment on Wikipedia | last = Skeptical About Skeptics | first = | authorlink = | date = | website = Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation | last = Bundrant | first = Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog | date = Apr 15, 2015 |access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url = https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog | date = Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="Steinemann2018" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name="TaskForce2017" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref name="siege2013">{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege | date = Jun 26, 2013|quote="In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."}}</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last = Gale | first =Richard | last2 = Null | first2 = Gary | title = Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network | date = Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref name="Lees1998">{{citation | first = Paul R | last = Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog | date = Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last = Gavura | first = Scott | title = Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog | date = Jul 3, 2014}}</ref><ref name="LeesMold2002">{{citation|last =Lees-Haley|first =Paul R. | title=Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog | date = Dec 23, 2002}}</ref><ref name="Probe1999">{{citation | title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03 | date = Jan 1, 1999 | last = D.R.Z.}}</ref><ref name="Hall-Rea">{{citation | last = Hall | first = Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref name="MacBeth2018">{{citation|last =MacBeth | first = Braden|title = Afflicted and the Tragedy of Fake Illnesses | date = Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref name="BarrettQuestionable">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Questionable Organizations: An Overview | date = Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref name="BarrettVulberability">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Vulnerability to Quackery | date = Jan 16, 2019}}</ref><ref name="Barrett-AAEM">{{Citation | last = Barrett | first = Stephen | title = Regulatory Actions against AAEM Members|publisher=Quackwatch blog | date = Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref name="BarrettOilyphyria">{{Citation | last = Barrett | first = Stephen | title = The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog | date = Jan 22, 2010}}</ref><ref name="BarrettProclam">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = MCS Proclamations}}</ref><ref name="BarrettGWI-MCS">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | first2 = Ronald E | last2 = Gots | title = Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref name="BarrettFad">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Be Wary of "Fad" Diagnoses | date = Oct 6, 2018}}</ref><ref name="BarrettIndex">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis? | date = Mar 28, 2019}}</ref><ref name="BarrettCloseLook">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = A Close Look at "Multiple Chemical Sensitivity" | date = 1998}}</ref><ref name="resolution21">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity | date = Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation | last = Barrett | first = Stephen|publisher=Quackwatch blog | title = Multiple Chemical Sensitivity: A Spurious Diagnosis | date = Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref name="CaseWP2009">{{citation | url =https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf | title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York | date = Nov 24, 2009}}</ref><ref name="WP-cap" /><ref name=":20">{{citation|last = Gale | first =Richard | title = Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url = http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network | date = Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref name="NcCarthyism">{{Cite web|url=https://prn.fm/stephen-barrett-medical-mccarthyism/ | title = Stephen Barrett and Medical McCarthyism|website=The Progressive Radio network blog|access-date= Feb 21, 2020}}</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name="ch1.4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref name="siege2013"/> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name="TaskForce2017" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name="Schwenk2004" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name="NICNAS" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name="Ch4.1-Noharm" /><ref name="VictorianHosp" /><ref name="NSW-factsheet" /><ref name="Mercy1999" /><ref name="Hosp2017" /><ref name="canberra2018" /><ref name="WA2019" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name="Aus-HR">{{citation | date = 2007 | title=Australian Human Rights Commission Access: Guidelines and information | last = Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation | last =Michaels | first = Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf | title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization | date = 2013 |quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>
==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ | title = "Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films | last = | first = | date = Nov 25, 2015 | website = YouTube | archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10 | title = Todd Haynes and Julianne Moore on Safe | last = | first = | date = |website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation | title = The 1995 film ‘Safe’ has new meaning during our coronavirus isolation | last = Di Corpo | first = Ryan | authorlink= | date = April 11, 2020 | website = |archive-url=|archive-date=|access-date = December 31, 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url = https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries | date = Sep 18, 2018}}</ref>
==Notable studies and publications==
*1987, Cullen, M.R. The worker with multiple chemical sensitivities: An overview<ref name="Cullen1987">{{Cite journal | title = The worker with multiple chemical sensitivities: an overview | date = Oct 1987|url=https://pubmed.ncbi.nlm.nih.gov/3313760/|journal=Occupational Medicine (Philadelphia, Pa.)|volume=2|issue=4 | pages = 655–661 | last = Cullen | first = M.R. | authorlink = |doi=|pmc=|pmid=3313760|access-date=|issn=0885-114X|quote=|via=}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/3313760 (Abstract)]

*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2005, Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition<ref name="Lacour2005">{{Cite journal | title = Multiple Chemical Sensitivity Syndrome (MCS) – suggestions for an extension of the US MCS-case definition | date = 2005-05-13|url=https://www.sciencedirect.com/science/article/pii/S1438463905000210|journal=International Journal of Hygiene and Environmental Health|volume=208|issue=3|pages=141–151 | last = Lacour | first = Michael | last2 = Zunder | first2 = Thomas | last3 = Schmidtke | first3 = Klaus | last4 = Vaith | first4 = Peter | last5 = Scheidt | first5 = Carl|language=en|doi=10.1016/j.ijheh.2005.01.017|issn=1438-4639}}</ref> - [https://www.sciencedirect.com/science/article/pii/S1438463905000210 (Abstract)]

*2014, Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity<ref name="Horowitz2014">{{Cite journal | title = Toxicant-Induced Loss of Tolerance: A Theory to Account for Multiple Chemical Sensitivity | date = Apr 2014|url=https://www.liebertpub.com/doi/pdf/10.1089/act.2014.20201|journal=Alternative and Complementary Therapies|volume=20|issue=2 | pages = 96–100 | last = Horowitz | first = Sala | authorlink = |doi=10.1089/act.2014.20201|pmc=|pmid=|access-date=|issn=1076-2809|quote=|via=}}</ref> [https://www.niehs.nih.gov/news/assets/docs_a_e/download_background_material_toxicantinduced_loss_of_tolerance_by_claudia_miller_508.pdf (Full text)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2016">{{Cite journal | last = | first = | authorlink = |vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al. | date = 2016-12-09 | title = Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives<ref name="Rossi2018" /> - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal | last = Viziano | first1 = A. | last2 = Micarelli | first2 = A. | last3 = Pasquantonio | first3 = G. | last4 = Della-Morte | first4 = D. | last5 = Alessandrini | first5 = M. | date = Nov 2018 | title = Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8 | pages = 923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]

*2019, International prevalence of chemical sensitivity, co-prevalences with asthma and autism, and effects from fragranced consumer products<ref name="Steinemann2019-international" /> - [https://link.springer.com/article/10.1007/s11869-019-00672-1 (Full text)]
*2021, Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity<ref name="Mazzatenta2021">{{Cite journal | title = Volatile organic compounds (VOCs) in exhaled breath as a marker of hypoxia in multiple chemical sensitivity | date = 2021 | url=https://onlinelibrary.wiley.com/doi/abs/10.14814/phy2.15034|journal=Physiological Reports|volume=9|issue=18|pages=e15034 | last = Mazzatenta | first = Andrea | last2 = Pokorski | first2 = Mieczyslaw | last3 = Giulio | first3 = Camillo Di|language=en|doi=10.14814/phy2.15034|pmc=PMC8449310|pmid=34536058|issn=2051-817X}}</ref> - [https://physoc.onlinelibrary.wiley.com/doi/full/10.14814/phy2.15034 (Full text)]
*2021, Mast cell activation may explain many cases of chemical intolerance<ref name="Miller2021">{{Cite journal | title = Mast cell activation may explain many cases of chemical intolerance | date = 2021-11-17|url=https://doi.org/10.1186/s12302-021-00570-3|journal=Environmental Sciences Europe|volume=33|issue=1|pages=129 | last = Miller | first = Claudia S. | last2 = Palmer | first2 = Raymond F. | last3 = Dempsey | first3 = Tania T. | last4 = Ashford | first4 = Nicholas A. | last5 = Afrin | first5 = Lawrence B.|language=en|doi=10.1186/s12302-021-00570-3|issn=2190-4715}}</ref> [https://link.springer.com/article/10.1186/s12302-021-00570-3 (Full text)]
*2021, Multiple Chemical Sensitivity<ref name="Zucco2021">{{Cite journal | title = Multiple Chemical Sensitivity | date = 2021-12-29|url=https://www.mdpi.com/2076-3425/12/1/46/htm|journal=Brain Sciences|volume=12|issue=1 | pages = 46 | last = Zucco | first = Gesualdo M. | last2 = Doty | first2 = Richard L.|doi=10.3390/brainsci12010046|issn=2076-3425}}</ref> [https://www.mdpi.com/2076-3425/12/1/46/htm (Full text)]

==News articles and interviews ==
*2017, [https://web.archive.org/web/20200215070226/https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world] - New Zealand Listener

*2018, [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condtion that affects one million Australia] - SBS television, Australia (Video)
*2019, [https://www.theguardian.com/lifeandstyle/2019/sep/15/fragrance-sensitivity-why-perfumed-products-can-cause-profound-health-problems Fragrance sensitivity: why perfumed products can cause profound health problems] - The Guardian

*2020, [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds] - Melbourne University Press
*2020, [https://i.stuff.co.nz/life-style/homed/kitchen/300272316/are-scented-cleaning-products-making-you-sick Are scented cleaning products making you sick?] - Stuff NZ
*2021, [https://www.washingtonpost.com/health/medical-mysteries/headache-chemical-smell-medical-mystery/2021/09/24/16c427ea-f2ec-11eb-a49b-d96f2dac0942_story.html The unusual headaches that upended this man's life began with a new car] - The Washington Post
*2021, [https://www.smh.com.au/national/experts-disturbed-over-toxic-discovery-in-popular-makeup-products-20210626-p584k2.html Experts ‘disturbed’ over toxic discovery in popular makeup products]<ref name="Whitehead2021">{{Cite journal | title = Fluorinated Compounds in North American Cosmetics | date = 2021-07-13|url=https://doi.org/10.1021/acs.estlett.1c00240|journal=Environmental Science & Technology Letters|volume=8|issue=7 | pages = 538–544 | last = Whitehead | first = Heather D. | last2 = Venier | first2 = Marta | last3 = Wu | first3 = Yan | last4 = Eastman | first4 = Emi | last5 = Urbanik | first5 = Shannon | last6 = Diamond | first6 = Miriam L. | last7 = Shalin | first7 = Anna | last8 = Schwartz-Narbonne | first8 = Heather | last9 = Bruton | first9 = Thomas A. | last10 = Blum | first10 = Arlene | last11 = Wang | first11 = Zhanyun|doi=10.1021/acs.estlett.1c00240}}</ref> - Sydney Morning Herald

== See also ==
* [[Toxicant-induced loss of tolerance (TILT)]]
* [[Mast cell activation syndrome]]
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[New allergies and intolerances]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf | title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome | last = Williams | first = Margaret | authorlink = Margaret Williams | date = Nov 10, 2010 | website = margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals
== References ==
{{reflist}}

[[Category:Allergy signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

User:Aletheia2020

2022-02-21T08:51:03Z

Aletheia2020:/* Causes */

''Hi,''

''I joined MEpedia solely to work on pages related to Multiple Chemical Sensitivity (MCS)—a common comorbid condition with ME''

== <big id="What_are_the_symptoms_of_multiple_chemical_sensitivity.3F">ALETHEIA'S SANDBOX (this is where I work on content)</big> ==
'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is a chronic acquired illness, in which sufferers report a range of symptoms when exposed to certain everyday chemicals.

One 2018 scientific review said the condition was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...|via=}}</ref> While another review, from the same year, said it was characterized by "susceptibility to a wide spectrum of environmental compounds, causing symptoms involving various organs and a decrease in quality of life."<ref name="pmid30088144" />

Commonly reported triggers for MCS symptoms include products like perfume, fresh paint fumes, tobacco smoke and mold.<ref name="Valderrama2015" /><ref name=":49" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref>

==Symptoms ==
The symptoms of MCS have been reported to affect multiple organs and body systems and to range from mild to disabling.<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Valderrama2015" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario:|publisher=Ministry of Health and Long-Term Care}}</ref><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|dead-url=y|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref>

A report from a national government inquiry into MCS found that the following symptoms—in this order—were the most commonly reported in MCS: headache, fatigue, confusion, depression, shortness of breath, arthralgia, myalgia, nausea, dizziness, memory problems, gastrointestinal symptoms, respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|dead-url=y|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> Other commonly reported symptoms of MCS include: cardiac arrhythmia, tachycardia, hypotension, hypertension, nausea, vomiting, skin rashes, visual disturbances, seizures, asthma and anaphylaxis.<ref name="Valderrama2015" /><ref name=":7" /><ref name=":6" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref>

A 2018 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />

The following substances have been reported as common triggers for MCS symptoms:
* synthetic fragrances,
* tobacco smoke,
* some pesticides, biocides and fungicides,
* some laundry detergents and fabric softeners,
* some petrochemical solvents (fumes from paint and polyurethane),
* formaldehyde,
* fumes from some building materials (particleboard and glues),
* some food additives and colorings (eg. tartrazine),
* some medications, and
* some anesthetics.<ref name="Rossi2018" /><ref name="Valderrama2015">{{citation|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref><ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures:|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" />

==Diagnosis ==
A 1999 international consensus on MCS is the most common diagnostic criteria used to diagnose the condition. This consensus was published in ''The Archives of Environmental Health,'' as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers, with different points of view about MCS.<ref name="pmid10444033" /> The team agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name=":1">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Valderrama2015" />
The Quick Environmental Exposure and Sensitivity Inventory (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Valderrama2015" /><ref name=":6" /><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref>

MCS has also been identified as a common comorbidity of chronic fatigue syndrome (CFS) by several CS consensus documents:
# The 2003 Canadian Consensus Criteria<ref>[[Bruce Carruthers|Carruthers, Bruce M.]]; [[Anil Kumar Jain|Jain, Anil Kumar]]; [[Kenny De Meirleir|De Meirleir, Kenny L.]]; [[Daniel Peterson|Peterson, Daniel L.]]; [[Nancy Klimas|Klimas, Nancy G.]]; [[Martin Lerner|Lerner, A. Martin]]; [[Alison Bested|Bested, Alison C.]]; [[Pierre Flor-Henry|Flor-Henry, Pierre]]; [[Pradip Joshi|Joshi, Pradip]]; [[A C Peter Powles|Powles, A C Peter]]; [[Jeffrey Sherkey|Sherkey, Jeffrey A.]]; [[Marjorie van de Sande|van de Sande, Marjorie I.]] (2003), [http://www.meresearch.org.uk/wp-content/uploads/2012/11/2003-Carruthers-Canadian-Definition-JCFS.pdf "Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols"] (PDF), ''Journal of Chronic Fatigue Syndrome'', '''11''' (2): 7-115, [[Digital object identifier|doi]]:[https://doi.org/10.1300%2FJ092v11n01_02 10.1300/J092v11n01_02]</ref> lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The 2011 International Consensus Criteria<ref>[[Bruce Carruthers|Carruthers, Bruce M.]]; [[Marjorie van de Sande|van de Sande, Marjorie I.]]; [[Kenny De Meirleir|De Meirleir, Kenny L.]]; [[Nancy Klimas|Klimas, Nancy G.]]; [[Gordon Broderick|Broderick, Gordon]]; [[Terry Mitchell|Mitchell, Terry]]; [[Donald Staines|Staines, Donald]]; [[A C Peter Powles|Powles, A. C. Peter]]; [[Nigel Speight|Speight, Nigel]]; [[Rosamund Vallings|Vallings, Rosamund]]; [[Lucinda Bateman|Bateman, Lucinda]]; [[Barbara Baumgarten-Austrheim|Baumgarten-Austrheim, Barbara]]; [[David Bell|Bell, David]]; [[Nicoletta Carlo-Stella|Carlo-Stella, Nicoletta]]; [[John Chia|Chia, John]]; [[Austin Darragh|Darragh, Austin]]; [[Daehyun Jo|Jo, Daehyun]]; [[Donald Lewis|Lewis, Donald]]; [[Alan Light|Light, Alan]]; [[Sonya Marshall-Gradisnik|Marshall-Gradisnik, Sonya]]; [[Ismael Mena|Mena, Ismael]]; [[Judy Mikovits|Mikovits, Judy]]; [[Kunihisa Miwa|Miwa, Kunihisa]]; [[Modra Murovska|Murovska, Modra]]; [[Martin Pall|Pall, Martin]]; [[Staci Stevens|Stevens, Staci]] (Aug 22, 2011). [https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1365-2796.2011.02428.x "Myalgic encephalomyelitis: International Consensus Criteria"]. ''Journal of Internal Medicine''. '''270''' (4): 327–338. [[Digital object identifier|doi]]:[https://doi.org/10.1111%2Fj.1365-2796.2011.02428.x 10.1111/j.1365-2796.2011.02428.x]. [[International Standard Serial Number|ISSN]] [https://www.worldcat.org/issn/0954-6820 0954-6820]. [[PubMed Central|PMC]] [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3427890 3427890] . [[PubMed Identifier|PMID]] [[pubmed:21777306|21777306]].</ref> lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. CFS Clinician Coalition lists "chemical sensitivity" as a symptom of CFS and MCS as a comorbidity.<ref>U.S. ME/CFS Clinician Coalition (Aug 2019). [https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view][https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view "Diagnosing and Treating ME/CFS"]</ref>

==Management ==
There is no clinically proven cure for MCS.<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name=":7" /> There is also no consensus on supportive therapies. But the literature does agree on the need for patients with MCS to avoid the specific substances that they have found trigger reactions for them.<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":7" /><ref name=":6" /><ref name="Genuis2013" />

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="Rossi2018" /><ref name="pmid30088144" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial,<ref name="pmid30088144" /> while some clinicians recommend using medical Oxygen to reduce the severity of symptoms during unavoidable or following accidental exposures to triggering substances.<ref name=":6" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>
== Epidemiology ==
While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="pmid30088144" /><ref>{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|dead-url=y|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Valderrama2015" /><ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref>

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Steinemann2005" /><ref>{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref> In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" /><ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref>{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|dead-url=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare condition.

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10">{{citation|trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|dead-url=y|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref>{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=www.cdc.gov|language=en-us|archive-url=|archive-date=|dead-url=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

==Causes ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":5">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia||dead-url=y|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggestedthat hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name=":5" />

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc = 1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in Gulf war syndrome or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc = 3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48" />

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc = 3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc = 3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name=":0">{{citation|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> (for example, "dizziness, seizures, head pain, fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and sensitization are widely thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name=":0" /><ref name=":17" /><ref name=":18" /><ref name=":16" />

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018" />{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name=":12">{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994" /><ref name="Davidoff1996" />

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref>{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc = 1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|dead-url=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

==In the media==
===Safe (1995) ===
''Safe'' is a cult film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

''Safe'' tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home. With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" /><div role="note" class="hatnote navigation-not-searchable"></div>

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last1=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144|pmc=|quote=|last6=|}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
:Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name=":1" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref>{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|dead-url=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

[[:Category:Sensitivity signs and symptoms]]
[[:Category:Neurological signs and symptoms]]
[[:Category:Immune signs and symptoms]]
[[:Category:Sensitivity signs and symptoms]]
[[:Category:Diagnoses]]
[[:Category:Environmental toxicology]]
== Cut content ==
They have also been found to decrease the quality of life of sufferers.<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" /><ref name="Steinemann2018" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009" /><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

== References ==
{{reflist}}

Talk:Multiple chemical sensitivity

2022-02-21T08:19:07Z

Aletheia2020:/* What's in a name? Adding synonyms to the introductory sentence and redirect pages -- Silliestchris (talk) 22:53, October 1, 2021 (UTC) */

==Biological/ Physiological or Psychological or Both==
Is this sentence from Possible causes correct and up to date? Are there better references for this? I thought much of the research was moving towards biological / physiological with any psychological factors being secondary. [[User talk:Aletheia2020]] ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 03:18, January 8, 2022 (UTC)

::'''These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.'''

===Old messages===

== Formatting problem with references -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:04, June 4, 2020 (EDT) ==

There seems to be a problem with some references disappearing. They remain as numbers without the reference. This seemed to start after the insertion of "see also"s, although I don't know if it's related.

Does anyone know how to fix? Thanks [User talk:Aletheia2020|talk]])

:I have only just seen this. Which references are affected? If the text looks OK but the references list has entries like: <nowiki > 20. ^ </nowiki > then click on the up arrow symbol and it should show you whwre it comes from. The source editor view can then be used to see what the issue is. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:57, June 30, 2020 (EDT)
::Fixed some time ago I think. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 03:18, January 8, 2022 (UTC)

== Images -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:16, May 16, 2020 (EDT) ==

Could anyone please direct me to where I can read about policies relating to image use.

Also, I uploaded three images and they didn't seem to be well formatted on the mobile app, with the image apearing in the middle of sentences. I tried to fix, but unless my mobile is showing the old version, I'm not sure how to fix it, if anyone can help. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:16, May 16, 2020 (EDT)Aletheia2020

::It looks like I missed answering this before. [[MEpedia:Copyright policy]] says which image rights are needed for reuse on MEpedia, [[Help:Images]] and [[Help:Files]] have further info including where to find some. Google's images search allows you to do an advanced search for "images for reuse", then you just need to double check on the page which license they are under. Photos and original computer graphics you made can be uploaded too. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 22:31, September 27, 2021 (UTC)

==Electrohypersensitivity==
Does this belong as part of the page, or is it better on a separate page? Are there specific types or subtypes of MCS to cover?
If EHS goes on this page this this image
and reference look worth adding. Skin lesions on a patient with [[electrohypersensitivity]] (EHS).
[[File:Electrohypersensitivity_MCS_skin_lesions.png|thumb|center|200px|[https://doi.org/10.3390/ijms21061915 Skin lesson caused by electrohypersensitivity. Source: 2020, Belpomme and & Irigaray. Int. J. Mol. Sci. 2020, 21(6), 1915.]]]
*2020, Belpomme, Dominique; and Irigaray, Philippe. Electrohypersensitivity as a Newly Identified and Characterized Neurologic Pathological Disorder: How to Diagnose, Treat, and Prevent It. Int. J. Mol. Sci. 2020, 21(6), 1915.<ref name="Belpomme2020">https://doi.org/10.3390/ijms21061915</ref> - [https://doi.org/10.3390/ijms21061915 (Full text)]
Could MCS be broken down into Electrohypersensitivity, Food/drink allergies and intolerances, and chemical/environmental allergies and sensitivities? The MCSAware website (for instance) seemed to concentrate on those areas. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 20:43, May 14, 2020 (EDT)

===Re: Electrohypersensitivity -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:56, June 4, 2020 (EDT)===

:Thanks for raising this. It's important. EHS is included under the umbrella term Idiopathic Environmental Intolerances, but most of the researchers into MCS don't like this term, since it has certain political associations. I think the consensus would say that EHS is a commonly comorbid condition to MCS and ME/CFS. I think it needs its own page.

:Likewise, food/drink allergies and intolerances are not MCS, which has a specific diagnostic criteria. Even though, many people with MCS do have food intolerances as well.[User talk:Aletheia2020|talk]])

===Re: Electrohypersensitivity -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 05:29, September 23, 2021 (UTC)===

: Hi, anectodally I have observed that EHS and MCS seem to be comorbid for some people. The Belpomme article really drives this home, as well. I think a statement should be made on the possible relationship, but EHS should have its own distinct page.

::There is now a basic stub page for [[Electrohypersensitivity]]. There are also pages aimed at ME/CFS for:
* [[Development of new sensitivities]]
* [[Chemical sensitivities]]
* [[Food sensitivities]]
* [[Medicine sensitivities]]
* [[Odor sensitivities]]

plus a number of other pages in [[:Category:Sensitivities]]. Info from MCS could be added under a subheading there.

The [[allergy]] page is a stub.

~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 22:31, September 27, 2021 (UTC)

==Scientific sources==
Some sources don't meet the [[MEpedia:Science guidelines]], which have been updated quite recently. Sources that are blogs, websites belonging to an individual or a small group, or patients have been used as sources (or in Learn more) in some places without making it clear whose view these are. Verywellhealth for instance is simply a patient/health website without medical oversight. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:43, May 13, 2020 (EDT)

===Re: Scientific sources -- [[User:JaimeS|JaimeS]] ([[User talk:JaimeS|talk]]) 13:24, May 15, 2020 (EDT)===

: Surprisingly, not a lot of scholarly articles on the controvery itself except in miniature: like, controversy of mast cells' role in neuroendocrinology.

:: I'm looking into this now. Will add a list here. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:51, May 15, 2020 (EDT)

==Popular culture==
This isn't a section we normally cover (see [[MEpedia:Article_outlines]] and I would like it remove it. This page is already very long. The popular culture pages here are only for NE/CFS, so if there is something notable covering ME/CFS and MCS it could have a separate page in the culture category. [[User:Aletheia2020]] [[User:Kmdenmark]] [[User:Pyrrhus]] [[User:JaimeS]]
I think the should also be less weight given to skeptics, Wikipedia and blogs in the controversy section. Wikipedia often includes excessive skeptical sources and excessive weight is given to them, but here we are mostly concerned with MCS as it relates to ME/CFS and possibly fibromyalgia or other comorbidities. Surely there should be some peer-reviewed research relating to the controversy? Articles on myths or misconceptions could be useful here, and in the Learn more section. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:43, May 13, 2020 (EDT)

===Re: Popular culture -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:55, May 14, 2020 (EDT)===

: Hey [[User:Notjusttired]] Thanks very much for taking the time to review the page and for your thoughts. I'm new to MEpedia so will rely on the adivce of more established users but this was my rationale.

I'll go through your points one by one.

CC: [[User:Pyrrhus]] [[User:JaimeS]]

'''Long, dense page''': I kept it all on one page primarily for SEO purposes, and following the Wikipedia model.

'''Popular culture:''' (taken from Wikipedia format) In the review of Safe, I tried to give a psychosocial perspective on how MCS is widely perceived and how this impacts the lives of sufferers. From my perspective, as an MCS sufferer, this is the more important section on the page because the scientific studies I don't think really describe how profound the social disslocation is that many people with MCS experience as a result of stigma.

'''Weight to skeptic argument:''' First, I do hear you on questioning my inclusion of this. I chose to cover it (what I see as the elephant in the room) because skeptics have dominated the Wikipedia page on MCS for many years. They delete anything there that contradicts their view and delete their accounts.

I hoped the summary of the controversy would give readers an intellectual and political context for Wikipedia's content--after all, Wikipedia has a big influence.

Also, because I'd read that Quackwatch and SBM invest a lot in their SEO, I thought that referring to many of their articles and using the language that they use to denigrate people with MCS may help the page's SEO. That hypothesis might have worked since the page has moved from page 30 to page 1 on a range of MCS search terms.

Re peer-reviewed research relating to this controversy, other than the consensus of last year (which said that the scientists arguing that MCS was psychologically-caused had conflicts of interest), I'm not aware of anything. It may be out there, but I've not seen it. Unfortunately, research into MCS has been limited.

'''General direction'''
I wrote this page for MEpedia on the understanding that this would just be a page about MCS--one that wasn't subject to the censorship restrictions of Wikipedia.

While there is a section on how it relates to ME, that certainly wasn't my goal in investing my time in this. My goal was to create
a reputable source that people with MCS could go to for resources and that they could direct others to (ie. loved ones, new friends, doctors, hospitals).

If MEpedia would prefer for the focus to be on how MCS relates to ME, I don't think I'd want to be involved with that. One, because I'm not an expert on that subject (I'm also not sure if much research has been done on that subject); and two, because I don't think it's what people with MCS need.

Sensitivities can be a symptom of ME, but MCS is a standalone condition, and I'd like it to get the space and spotlight it needs as a very serious standalone condition.

If MEpedia isn't the place for that, I understand. I also wish I'd known that before I'd given my content to MEpedia and invested a lot of time on the page. In light of that, I'd like to be able to take my content with me, if you decide to change the direction of the page significantly. I wrote all of it except for the section ME and MCS. It's the culmination of several years work for me, and I'd like to see it published somewhere.

[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:55, May 14, 2020 (EDT)Aletheia2020

:::Thanks for your reply [[User:Aletheia2020]]. I perhaps was a bit unclear about how it impacts ME - I think a stand alone page is incredibly useful, but any extra sources that cover it as a comorbidity of ME/CFS and/or fibromyalgia would be really useful. MCS is a huge complication for many with ME so the page is extremely useful. Similarly, the Fibromyalgia has ended up very long, there's a separate [[Fibromyalgia drugs]] page - would a [[Fibromyalgia treatments]] summary page be helpful? Anything that could be added to individual treatment pages about MCS would be helpful, just add a subheading for it (not sure what potions there are in terms of management / treatments).
I think if you have time, some of what is here would be useful on pages like [[Medically unexplained symptoms]], and [[psychologization]]. As regards SEO, the MediaWiki software controls so much of that. Things I've noticed that are very useful are adding some images (quotes or other pictures), careful wording of the first 2 lines of the article, increasing the number of subheadings and having subheadings related to things that are commonly searched for since these then appear as short links in the search results.
Perhaps the "popular culture" heading could be changed to something about what it's like to live with MCS?
Regarding the "learn more" section - are there some leaflets for patients or Consensus guidelines and criteria that could go there?
I've noticed the huge amount of work you are putting into the page, I can't think you enough for that. :-) I see so many online struggling with MCS and with few reliable places to go, and difficulties explaining things to others. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 06:58, May 14, 2020 (EDT)

Thanks for your note and suggestions[[User talk:Notjusttired|talk]] and [[User:JaimeS]].

I took from your further comments that you're OK with leaving the page generally as is but that you wanted the popular culture section changed and more on how MCS impacts ME. Is that right? Or do you still think further sections should be cut, reduced or separated out onto other pages?

As for how MCS impacts ME, I agree it's an important subject, and it's actually not one I had thought much about until this conversation.

Myself I have both conditions, and I would say that out of the people I know with severe and longstanding MCS, the majority seem to also have ME.

From my perspective, the biggest complication MCS creates for a person who also has ME is access/disability issues, which can greatly compromise getting accommodation, support and medical care. Of course, these disability aspects of MCS create these complexities for the sufferer in relation to any comorbid medical condition, not just ME. It complicates them getting medical care for MCS symptoms.

Access issues is a section I've been meaning to write (and it's alluded to in hospital care). I've been procrastinating on it cos it's literally such a big subject, I'm still figuring out how to summarise it into a small section.

So, im summary, I agree that this subject is important. It's just not what I had in mind when I wrote this page page. And to me it seems a bit specific for this page.

I wrote this page with a general, unninformed target audience in mind, hence talking a little about a wide range of subjects, with the idea that the reader could come to the page with literally no idea what MCS is.

In contrast, how MCS impacts ME would be for an informed audience (ie. mostly likely people with both conditions or their loved ones or carers).

As for SEO, the reason I started paying more attention to that, is that when the page was first up (for the first month or so), it was coming up around page 30 on Google--really too deeply buried to make a difference for random searches. I consulted an SEO expert and he suggested incorporating certain words and questions into the content, where possible. Two weeks after I started doing that, I noticed the page coming up much higher in Google for certain subjects. And it seemed to come up higher still the more I did it. It wasn't the only SEO tactic I used, so I don't know for sure whether it was responsible for it coming up higher, but I think it might have been.

Like you [[User talk:Notjusttired|talk]] the SEO consultant said that incorporating common googled phrases and questions in headings is the best, although I thought your page followed a similar template to Wikipedia in relation to headings, so didn't want to mess with them. It sounds like there is some flexibility there, though?

On images [[User talk:Notjusttired|talk]], thanks, that's good to know. They would be good to incorporate. Is there a place that MEpedia contributors commonly get stock images?

And [[User:JaimeS]] with the Safe review having non-scientific resources quoted, I assumed this was OK because a movie review is a movie review--ie. it's not making any controversial scientific claims (and obviously there are no scientific sources about movies). I still thought there was value in quoting media and academic sources about the film because it gives a glimpse into the director's intent and how it was widely interpreted.

I see that Safe has been shortened and some of that content moved to the Safe page. Wasn't sure if that related to the sources I'd used to you just wanting to shorten it.

But I wonder if you'd consider leaving it as is. I ask because the review was carefully written, dense with terms and phrases that I thought could potentially help SEO. It was easier to do that in this section because it had freer form that the scientific sections.

As well, I think the detail about Safe is important because it's not a straight-out narrative about someone having MCS.

The film is actually very vague about what's happening to Carol and why (even though it's a perfectly realistic depiction of what MCS looks like). This vagueness is probably why the film was interpreted in many diverse ways (eg. as a horror film, as a feminist film).

The summary as brief as it is now I don't think really conveys the nuance of how nuance of how the condition is presented. For example, I think it's an important detail to include that nowhere in the film does it mention MCS. It's just that Haynes has confirmed that this was the condition he wrote the film about. Haynes actually wrote the film as a metaphor for how patients with AIDS were treated. I didn't go into that cos it did seem like unnecessary detail for the MCS page, but, basically, Safe isn't a clear cut film about MCS.

Also, I thought because it is at the bottom of the page, I didn't think it would distract from other content by being a little detailed.

Finally re Mepedia policies, apologies if I haven't adhered to all of them and for the time it takes other editors to fix my mistakes [[User:JaimeS]] [[User talk:Notjusttired|talk]]. I did read through them at the start, and probably didn't retain all I read. I'll go over them again. But my memory isn't great, so thanks for nudges about times that I've deviated from them. [[User:Aletheia2020]]

Hello all, I am just coming up to speed on the discussion and I am very impressed with what, mainly, [[User:Aletheia2020]] has put together here. The MCS page has taken on a life of its own, and I think that Mepedia in general has grown into something far beyond what the founders originally envisioned. I actually found this page because I was appalled at the bias on wikipedia's MCS page. I used to donate to Wikipedia, but my donations will be going to Mepedia instead, now.

====Re: Re: Popular culture -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 19:29, May 16, 2020 (EDT)====

:: Replace this text with your reply

====Re: Re: Popular culture -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 00:07, September 26, 2021 (UTC)====

:: Replace this text with your reply

===Re: Popular culture -- [[User:JaimeS|JaimeS]] ([[User talk:JaimeS|talk]]) 13:13, May 15, 2020 (EDT)===

: I agree that the section that exists now is a little over-sourced and could be edited down. Re: censorship, I know that Wikipedia has a really frustrating and demeaning history of falling on the side of reactionary skepticism/mockery of people with chronic conditions. MEpedia is moderated by a patient advocacy organization, not would not seek stifle the voice of people with chronic conditions.

I think you and I have had conversations on this, Aletheia2020! You know I agree with you that good information should be available for those who seek it. As I mentioned when we spoke about this, we do have particular requirements for which sources are considered scholarly, and some general editing rules of thumb (like how many sources are cited per fact). You can find most of these in the science guidelines (http://me-pedia.org/wiki/Science_Guidelines).

Since this is a Wiki, the page would be open to improvement by anyone at any time. In the case of vandalism or unhelpful edits, we have the ability to revert to the previous edits, but locking a page indefinitely after one set of edits would be something we would only do if we were seeing (or suspected we would see) repeated vandalism on the page.

[Edit -- reading quickly through, let me know if there's anything I've missed.]

== Missing reference #19 -- [[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 23:52, February 9, 2020 (EST) ==

[[User:Aletheia2020]] Thanks for your great work on this page! There is one reference missing though, currently numbered #19. Please double-check. Thanks again.
<br>[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 23:52, February 9, 2020 (EST)

:[[User:Pyrrhus]] Thank you, and sorry about that reference. For some reason, a few disappeared. It will take me a bit of time to work out which ones went missing when I cut and pasted. I'll try to fix it in the coming days <br>[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]])

== First section on chemical sensitivities in ME/CFS ==

Hey, I wasn't sure who edited this section, but I envisaged this page as one about MCS as a standalone condition--a condition which is commonly comorbid with ME/CFS. I didn't want it to be chemical sensitivities or MCS in ME/CFS, since the content that follows that section isn't that.

I was going to change it back, but if you don't agree, happy to chat about it.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:17, February 12, 2020 (EST)Aletheia2020

:I'm afraid I don't understand what exactly you are referring to. Could you clarify? Generally speaking, pages on MEpedia should state at the outset what the relevance to ME/CFS is. This section is usually titled "Such-and-such in ME/CFS". The point of the section is to explain why this topic is RELEVANT to ME, to avoid having the page deleted for falling outside the scope of MEpedia. The merits of considering a particular condition as a COMORBIDITY are typically covered in a separate section. I hope this helps.
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 20:51, February 10, 2020 (EST)

::Hey [[User:Pyrrhus]] thank you for the extra details. I understand.

::My concerns is that medication, food and odour sensitivities are not MCS and the way that the paragraph is now phrased makes it a little confusing on a page about MCS--especially when it's the first section after the intro.

::MCS has specific diagnostic criteria, and, yes, it often is accompanied by medication, food and odour sensitivities, but not always. And the MCS community has some good reasons to distinguish between odour and chemical sensitivities because different studies and conclusions apply to these two phenomenon.

::If you'd rather leave the title like that because its your convention, no worries. I think that works OK.

::But I think that taking the paragraph back to what I had would make it clearer about what MCS is. Food sensitivities etc are really for a whole nother page.

::Also, I spelled out ME/CFS here since it's the first time it's mentioned on the page and people may come to this page from Googling MCS and not know what ME/CFS is. I also thought it important to specify that the consensus documents were about ME/CFS since it's not clear otherwise what they are consenses about.

::What do you think?[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:17, February 12, 2020 (EST)Aletheia2020

:::You make some very good points [[User:Aletheia2020]]. Give me a little time to incorporate your points into a draft section, which I will post here on the discussion page for you to review and edit. Thanks.
:::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:41, February 12, 2020 (EST)

:::Okay, [[User:Aletheia2020|Aletheia2020]], how does the following section look?
:::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 20:59, February 12, 2020 (EST)

::::Thanks for doing that [[User:Pyrrhus|Pyrrhus]]. Looks good. I think that that is very clear. Whether that level of detail is required above what was there before, I don't know. But I found it interesting to read the details.

::::The only thing I didn't agree with was the last bit, saying some studies differentiate odour and chemical sensitivities. I think it's a very important to make clear that MCS is not odour sensitivity. I think this is a common misconception.

::::If you look at the 1999 criteria for MCS (and proposed changes to that in the 2019 consensus) there is nothing about sensitivities to odours mentioned in the diagnostic criteria.

::::Some triggering chemicals have odours and some people with MCS have exaggerated senses of smell, but many triggering chemicals (eg. many pesticides) don't have a perceptible smell and many people with MCS have normal senses of smell, and some have no sense of smell at all (which makes avoiding triggers pretty tricky).

::::In my experience, studies into odour sensitivity are often more focused on a perceived nocebo/psychosomatic angle, and in relation to MCS, these have been used in attempts to discredit MCS as a physical disorder. So I'd rather keep my distance from them.

::::From what I can tell, the Quackwatch/SBM mob like to characterise MCS as something like: a bunch of hysterical women getting anxious, angry and upset when they smell perfume or petrol, in some kind of paranoid fit of chemophobia.

::::But this characterisation doesn't explain MCS when the triggering chemical has no smell or when the reaction is from topical contact, ingestion or injection (eg. in the case of anaesthetics, which are notorious for making people with MCS ill).

::::Anyway, in summary, I'd just cut the final sentence. I think the rest of the contact makes it clear MCS is not sensitivity to odours. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

:::::Thanks for all the background, [[User:Aletheia2020|Aletheia2020]]. I have learned a lot about MCS in this conversation. I think many people in the ME community, including those with MCS, are unaware that MCS has specific diagnostic criteria. So your work on this page helps a lot. I'll go ahead and cut the final sentence and then copy it over. Thanks again.
:::::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:17, February 14, 2020 (EST)

::::::It's really good to read that feedback : [[User:Pyrrhus|Pyrrhus]] -- thank you. I think the "is MCS real?" conversation has really eclipsed conversations about what the condition actually is. And that hasn't helped sufferers. Hopefully this page is of use to other people with chemical sensitivities or MCS.

::::::Also, thank you also for your patience with me as I've been learning how things work on here.````Aletheia2020

<div style="background:#FFFFE0;border:1px dotted black">
== MCS in ME and ME/CFS ==
MCS has been described as a comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) and [[fibromyalgia]].<ref>{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref>{{Cite news|url=https://www.verywellhealth.com/fibromyalgia-comorbid-overlapping-conditions-716184|title=Illness That Come Along with Fibromyalgia & Chronic Fatigue Syndrome|last=Dellwo|first=Adrienne|authorlink=Adrienne Dellwo|date=Feb 26, 2018|work=Verywell Health|access-date=2018-08-23|archive-url=|archive-date=|url-status=}}</ref> The [[Canadian Consensus Criteria]] for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and lists "Multiple Chemical Sensitivities (MCS)" as a comorbidity. The [[International Consensus Criteria]] for diagnosing myalgic encephalomyelitis (ME) lists "sensitivities to food, medications, odours or chemicals" as a symptom and lists "multiple chemical sensitivities" as a comorbidity. A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and lists "Multiple Chemical Sensitivities" as a commonly comorbid condition.<ref>“Diagnosing and Treating ME/CFS” by the U.S. ME/CFS Clinician Coalition, August 2019. https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view</ref>

However, it is important to note that MCS has specific diagnostic criteria which do ''not'' include medication, food or odor sensitivities.<ref name="pmid10444033" /> Furthermore, some studies have differentiated odor sensitivity and chemical sensitivity as two separate phenomena.{{citation needed}}
</div>

== On This is a Potential comorbidities page ==
I wondered how we can resolve whether it is or isn't a comorbidity. I know the US Coalition on ME/CFS consensus from last year said it was, but I'm really not up on other ME/CFS stuff.

I think removing the banner would look better if it can be agreed either way.

Thanks <br>[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]])

:A page is expected to objectively weigh the evidence for and against considering a condition as a comorbidity. As much as possible, we leave it up to the reader to draw their own conclusions. Because of this, we recently renamed our "Comorbidities" category to "Potential comorbidities", in order to let the page itself weigh the evidence, and in order to let the reader come to their own conclusion.

::[[User:Pyrrhus]] OK, got it. Thanks [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

:These sorts of debates just don't belong in category-naming decisions. Categories are simply a convenient way to group articles, nothing more, and we don't want to complicate things by politicizing category names. We did the same thing with the "Treatments" category, which is now called "Potential treatments". With that said, the banner is indeed ugly and distracting. We have developed a better banner and are (still) waiting for our technical people to finally implement the better banner. For the time being, we just have to put up with the current ugly and distracting banner...

::[[User:Pyrrhus]] OK. That's good to know. Yes, it's very dominating as it is atm. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

:Hope this helps. Please let me know if you have any further questions.
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:07, February 10, 2020 (EST)

::Oops, [[User:Aletheia2020]], I forgot to mention that the word "comorbidity" on MEpedia has a specific meaning: it means a condition that is statistically more likely to be found in the original condition, than it is to be found in the general population. I only mention that since there are other definitions out there...
::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:28, February 10, 2020 (EST)

::::[[User:Pyrrhus]] OK, noted. I'll stick with your definition. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

== English or American spelling? ==

[[User:Pyrrhus]] I noticed that you changed some ss to zs in words but changed centers to centres. So I was unsure if you went with American or English spelling on this page? Thanks [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:44, February 12, 2020 (EST)Aletheia2020

:The [[MEpedia:Manual of style]] specifies American spelling and dates, which I why I changed some spelling, including changing "centres" to "centers". Then I realized that the word "centres" was part of a quote from a Canadian, so I changed "centers" back to "centres". I hope this clarifies things. Good catch!
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:48, February 12, 2020 (EST)

::Ah, I got it [[User:pyrrhus|pyrrhus]]. No worries.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

== Questionable comparison that could be interpreted as bias ==

[[User:Aletheia2020|Aletheia2020]], I notice that you make a comparison between "merchants of doubt", who are paid to disseminate disinformation that they don't themselves believe, and intolerant skeptics, who may use similar tactics but are unpaid and actually believe what they are claiming. Some may say that this is an unfair comparison that displays bias on our part. Perhaps rephrase?
<br>[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 14:34, February 12, 2020 (EST)

===Re: Questionable comparison that could be interpreted as bias -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:47, February 12, 2020 (EST)===

: I hear you, and they are good points. But I used the comparison (and think it's important) because Barrett, Gots and Quackwatch have been documented to receive corporate funding.

: As well, I don't think "controversy" as the heading for the section originally labelled "politics" is accurate.

:In my view, the idea that there is a controversy has been manufactured, and I don't want to give it any more oxygen by using a heading that reinforces the idea that there is a heated academic debate going on about MCS being real or not when there isn't.

:In the case of MCS, the views of SBM and Quackwatch are fringe. I also don't consider them genuine skeptics. I know the president of the national association of skeptics, and he thinks SBM is very little to do with skeptic philosophy and a lot to do with pursuing an already-decided agenda. So it's an ideology, not a method for critical thinking.

:No academic review on MCS studies that I've seen has concluded the condition is fake or bogus. Certainly this isn't the conclusion of at least the past five large-scale reviews.

:I called this section politics, to show that there are powerful interests involved, which have influenced the debate and are continuing to influence it (just as we have seen with tobacco, DDT, asbestos and now climate change).

:The most recent large-scale academic review of MCS studies in 2019 (the Italian consensus) even said that the few studies claiming a psychological cause all had clear conflicts of interest and could not be considered reliable on that basis alone (in addition to the methological criticisms levelled at those studies).[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:47, February 12, 2020 (EST)Aletheia2020

::Thanks for sharing some of the backstory here. What you describe is perfectly familiar to the ME community. We also have powerful interests who prominently claim that ME is a fake disease, receive funding from insurance companies to give speeches to doctor conventions "informing" them that ME is a fake disease, are paid by the insurance companies to testify at disability pension hearings to deny disability payments to ME patients, who then have no choice but to commit suicide.

::These powerful interests have even gone so far as to set up their own academic journals to publish their "peer-reviewed" work, and have set up their own media organization to plant stories in various newspapers claiming that bedridden ME patients are plotting to assassinate innocent scientists. (not a joke)

::Yes, it's immensely frustrating that, in these days, anyone can manufacture a controversy simply by stating that a controversy exists. If we were a public relations organization, we would gladly ignore all manufactured controversies. But we're an encyclopedia, and we have a duty to objectively report on all controversy, regardless of the controversy's merit (or lack thereof).

::MEpedia's editorial guidelines (see [[MEpedia:POV]]) state that section headings describing controversies can be titled "Controversy" or "Criticism". I chose the word "Controversy" because "Criticism" implies legitimate criticism, but the word "Controversy" does not.

::And I don't think you have to worry about readers equating skepticism with critical thinking. The common use of the word "skeptic" is just someone who doubts something. (like a "climate skeptic" who doubts climate change) But if you fear readers may use a more nuanced definition of "skeptic", you can just refer to them as "critics" or "bloggers" instead of as "skeptics".

::Hope this helps. [[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:28, February 13, 2020 (EST)

::[[User:pyrrhus|pyrrhus]] OK. I understand. Thanks. And, yes, you're probably right that most people don't know much about the divisions in skeptic movements.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

==References==
{{reftalk}}

== Headings and SEO -- ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT) ==

Please avoid using questions as headings, and avoid using the page name within headings. The MediaWiki software is built by Wikipedia so should already be able to work out that a subheading is linked to the topic page, and phrasing the first line under the heading carefully should be enough, e.g. The symptoms of MCS include...". Headings should be worded as per the examples on [[MEpedia:Article outlines]].

SEO rankings increase when small pages cover the exact topic, e.g. you could create a few small page in the format of a '''list''', [[Multiple chemical sensitivity symptoms]] then use <code><nowiki >{{See also|Multiple chemical sensitivity}}</nowiki></code> to point back to the original page. The original page would a less detailed description of symptoms, and could use <nowiki >{{See also|Multiple chemical sensitivity symptoms}}</nowiki></code> to take users back to it. The new page would go in the [[Category:Lists]] and [[Category:Signs and symptoms]]. I am thinking of creating a list page for [[Deaths from myalgic encephalomyelitis/chronic fatigue syndrome]], so will be interested to see how this ranks compared to the [[causes of death]], [[Sophia Mirza]], and [[severe and very severe ME]] pages. (Sophia's is one of the top pages on MEpedia). ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT)

==Images==
I believe images would help SEO. If you would like a simple image creating eg for the symptoms, can you let me know what design and colors (green? primary colors?) you would like or links to any images with the layout you want. Images are highlighted by search engine results and encourage views and also get saved to pinterest which results in more views. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT)

== Additions to history -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 05:54, September 23, 2021 (UTC) ==

It could aid patient advocacy to put some precedent setting decisions in here. One court case example that comes to mind is the Canada Revenue Association vs a woman (a large MCS advocate in Canada, forget the name) who had claimed tax deductible renovations on her home to accommodate MCS. Would this be helpful here, or would a section on MCS in the court system be more suitable?

== MCS as a symptom of a disease, not a disease. -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 06:02, September 23, 2021 (UTC) ==

This is a controversial idea, I know, and I am not aiming to make any additions or changes. However, given the rapidly advancing state of knowledge on the underlying mechanisms of MCS, I think it will be helpful to have a discussion about this idea.

The more I learn about MCS and talk to people with it, the more it becomes apparent that the sensitivity is a symptom of underlying problems which are diverse, complex, and different for every individual. And yes, the underlying problems are almost universally caused or initiated by toxic exposure. One example is Mast Cell Activation Syndrome. Another is Oxidative Stress. You get the idea. Thoughts?

===Re: MCS as a symptom of a disease, not a disease. -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 08:12, February 21, 2022 (UTC)===

I agree with you. I think MCS is a sensitivity syndrome that likely has different causes in different people.

But I also think that for recognition purposes (eg. access policies) having it defined as a condition (even if that only means an array of symptoms provoked in particular ways) may be helpful.

Are you suggesting talking about this specifically or just changing reference words

== Additions to recognition section -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:02, September 23, 2021 (UTC) -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:02, September 23, 2021 (UTC) ==

It would be helpful for patients to add some more detail on legal recognition. For example, the Canadian Human Rights Commission has taken a rather firm stance on environmental sensitivities: https://www.chrc-ccdp.gc.ca/sites/default/files/policy_sensitivity_0.pdf

"Individuals with environmental sensitivities experience a variety of adverse reactions to environmental
agents at concentrations well below those that might affect the “average person”. This medical condition is a
disability and those living with environmental sensitivities are entitled to the protection of the Canadian
Human Rights Act, which prohibits discrimination on the basis of disability."

===Re: Additions to recognition section -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:02, September 23, 2021 (UTC) -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 08:15, February 21, 2022 (UTC)===

: I guess the issue with human rights recognition is that it doesn't mean anything in the medical world. So I kept the recognition section about medical index or medical college recognition

But I think using recognition by human rights agencies could be inserted in the access sections. I mention a ruling by the Australian HRC so perhaps the Canadian ruling could go alongside that?

Aletheia2020

== New references for notable studies section -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:38, September 23, 2021 (UTC) ==

A recent review paper, published in reviews on environmental health about a week ago, would be useful to have in this section:

https://www.degruyter.com/document/doi/10.1515/reveh-2021-0043/html

== What's in a name? Adding synonyms to the introductory sentence and redirect pages -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 22:53, October 1, 2021 (UTC) ==

MCS is known by many names, depending on the legal context and jurisdiction. For example, The Canadian Human rights commission likes to call it "environmental sensitivity" although this is a more broad umbrella term. Another term being used in pathophysiological literature is TILT. Some more examples:

Environmental illness
Chemical intolerance
Gulf War syndrome
Sick building syndrome

Or perhaps we should remove IEI from the first sentence altogether and have a section dedicated specifically to alternate names?

Thoughts?

===Re: What's in a name? Adding synonyms to the introductory sentence and stub pages -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 22:54, October 1, 2021 (UTC)===

: I think that environmental illness is too broad (I think it means any disease caused by the environment or by pollutants, so by definition, it could include cancers, parkinsons etc...I think it's more the umbrella term and I think the Canadian HRC are using it incorrectly re MCS

Chemical intolerance--again, I don't know how it's defined

Gulf war syndrome--specific and disintct from MCS

SIck building syndrome--think it has poor recognition?

The advantage of MCS and IEI is that they're the terms most commonly used in the medical reviews, the WHO's taskforce on the subject and the largest consensus papers on the condition, so I think it's better to stick with them

Aletheia2020

===Re: What's in a name? Adding synonyms to the introductory sentence and redirect pages -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 08:19, February 21, 2022 (UTC)===

: Replace this text with your reply

Talk:Multiple chemical sensitivity

2022-02-21T08:15:12Z

Aletheia2020:/* Additions to recognition section -- Silliestchris (talk) 16:02, September 23, 2021 (UTC) -- Silliestchris (talk) 16:02, September 23, 2021 (UTC) */

Talk:Multiple chemical sensitivity

2022-02-21T08:12:25Z

Aletheia2020:/* MCS as a symptom of a disease, not a disease. -- Silliestchris (talk) 06:02, September 23, 2021 (UTC) */

==Biological/ Physiological or Psychological or Both==
Is this sentence from Possible causes correct and up to date? Are there better references for this? I thought much of the research was moving towards biological / physiological with any psychological factors being secondary. [[User talk:Aletheia2020]] ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 03:18, January 8, 2022 (UTC)

::'''These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.'''

===Old messages===

== Formatting problem with references -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:04, June 4, 2020 (EDT) ==

There seems to be a problem with some references disappearing. They remain as numbers without the reference. This seemed to start after the insertion of "see also"s, although I don't know if it's related.

Does anyone know how to fix? Thanks [User talk:Aletheia2020|talk]])

:I have only just seen this. Which references are affected? If the text looks OK but the references list has entries like: <nowiki > 20. ^ </nowiki > then click on the up arrow symbol and it should show you whwre it comes from. The source editor view can then be used to see what the issue is. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:57, June 30, 2020 (EDT)
::Fixed some time ago I think. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 03:18, January 8, 2022 (UTC)

== Images -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:16, May 16, 2020 (EDT) ==

Could anyone please direct me to where I can read about policies relating to image use.

Also, I uploaded three images and they didn't seem to be well formatted on the mobile app, with the image apearing in the middle of sentences. I tried to fix, but unless my mobile is showing the old version, I'm not sure how to fix it, if anyone can help. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:16, May 16, 2020 (EDT)Aletheia2020

::It looks like I missed answering this before. [[MEpedia:Copyright policy]] says which image rights are needed for reuse on MEpedia, [[Help:Images]] and [[Help:Files]] have further info including where to find some. Google's images search allows you to do an advanced search for "images for reuse", then you just need to double check on the page which license they are under. Photos and original computer graphics you made can be uploaded too. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 22:31, September 27, 2021 (UTC)

==Electrohypersensitivity==
Does this belong as part of the page, or is it better on a separate page? Are there specific types or subtypes of MCS to cover?
If EHS goes on this page this this image
and reference look worth adding. Skin lesions on a patient with [[electrohypersensitivity]] (EHS).
[[File:Electrohypersensitivity_MCS_skin_lesions.png|thumb|center|200px|[https://doi.org/10.3390/ijms21061915 Skin lesson caused by electrohypersensitivity. Source: 2020, Belpomme and & Irigaray. Int. J. Mol. Sci. 2020, 21(6), 1915.]]]
*2020, Belpomme, Dominique; and Irigaray, Philippe. Electrohypersensitivity as a Newly Identified and Characterized Neurologic Pathological Disorder: How to Diagnose, Treat, and Prevent It. Int. J. Mol. Sci. 2020, 21(6), 1915.<ref name="Belpomme2020">https://doi.org/10.3390/ijms21061915</ref> - [https://doi.org/10.3390/ijms21061915 (Full text)]
Could MCS be broken down into Electrohypersensitivity, Food/drink allergies and intolerances, and chemical/environmental allergies and sensitivities? The MCSAware website (for instance) seemed to concentrate on those areas. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 20:43, May 14, 2020 (EDT)

===Re: Electrohypersensitivity -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:56, June 4, 2020 (EDT)===

:Thanks for raising this. It's important. EHS is included under the umbrella term Idiopathic Environmental Intolerances, but most of the researchers into MCS don't like this term, since it has certain political associations. I think the consensus would say that EHS is a commonly comorbid condition to MCS and ME/CFS. I think it needs its own page.

:Likewise, food/drink allergies and intolerances are not MCS, which has a specific diagnostic criteria. Even though, many people with MCS do have food intolerances as well.[User talk:Aletheia2020|talk]])

===Re: Electrohypersensitivity -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 05:29, September 23, 2021 (UTC)===

: Hi, anectodally I have observed that EHS and MCS seem to be comorbid for some people. The Belpomme article really drives this home, as well. I think a statement should be made on the possible relationship, but EHS should have its own distinct page.

::There is now a basic stub page for [[Electrohypersensitivity]]. There are also pages aimed at ME/CFS for:
* [[Development of new sensitivities]]
* [[Chemical sensitivities]]
* [[Food sensitivities]]
* [[Medicine sensitivities]]
* [[Odor sensitivities]]

plus a number of other pages in [[:Category:Sensitivities]]. Info from MCS could be added under a subheading there.

The [[allergy]] page is a stub.

~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 22:31, September 27, 2021 (UTC)

==Scientific sources==
Some sources don't meet the [[MEpedia:Science guidelines]], which have been updated quite recently. Sources that are blogs, websites belonging to an individual or a small group, or patients have been used as sources (or in Learn more) in some places without making it clear whose view these are. Verywellhealth for instance is simply a patient/health website without medical oversight. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:43, May 13, 2020 (EDT)

===Re: Scientific sources -- [[User:JaimeS|JaimeS]] ([[User talk:JaimeS|talk]]) 13:24, May 15, 2020 (EDT)===

: Surprisingly, not a lot of scholarly articles on the controvery itself except in miniature: like, controversy of mast cells' role in neuroendocrinology.

:: I'm looking into this now. Will add a list here. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:51, May 15, 2020 (EDT)

==Popular culture==
This isn't a section we normally cover (see [[MEpedia:Article_outlines]] and I would like it remove it. This page is already very long. The popular culture pages here are only for NE/CFS, so if there is something notable covering ME/CFS and MCS it could have a separate page in the culture category. [[User:Aletheia2020]] [[User:Kmdenmark]] [[User:Pyrrhus]] [[User:JaimeS]]
I think the should also be less weight given to skeptics, Wikipedia and blogs in the controversy section. Wikipedia often includes excessive skeptical sources and excessive weight is given to them, but here we are mostly concerned with MCS as it relates to ME/CFS and possibly fibromyalgia or other comorbidities. Surely there should be some peer-reviewed research relating to the controversy? Articles on myths or misconceptions could be useful here, and in the Learn more section. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 13:43, May 13, 2020 (EDT)

===Re: Popular culture -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:55, May 14, 2020 (EDT)===

: Hey [[User:Notjusttired]] Thanks very much for taking the time to review the page and for your thoughts. I'm new to MEpedia so will rely on the adivce of more established users but this was my rationale.

I'll go through your points one by one.

CC: [[User:Pyrrhus]] [[User:JaimeS]]

'''Long, dense page''': I kept it all on one page primarily for SEO purposes, and following the Wikipedia model.

'''Popular culture:''' (taken from Wikipedia format) In the review of Safe, I tried to give a psychosocial perspective on how MCS is widely perceived and how this impacts the lives of sufferers. From my perspective, as an MCS sufferer, this is the more important section on the page because the scientific studies I don't think really describe how profound the social disslocation is that many people with MCS experience as a result of stigma.

'''Weight to skeptic argument:''' First, I do hear you on questioning my inclusion of this. I chose to cover it (what I see as the elephant in the room) because skeptics have dominated the Wikipedia page on MCS for many years. They delete anything there that contradicts their view and delete their accounts.

I hoped the summary of the controversy would give readers an intellectual and political context for Wikipedia's content--after all, Wikipedia has a big influence.

Also, because I'd read that Quackwatch and SBM invest a lot in their SEO, I thought that referring to many of their articles and using the language that they use to denigrate people with MCS may help the page's SEO. That hypothesis might have worked since the page has moved from page 30 to page 1 on a range of MCS search terms.

Re peer-reviewed research relating to this controversy, other than the consensus of last year (which said that the scientists arguing that MCS was psychologically-caused had conflicts of interest), I'm not aware of anything. It may be out there, but I've not seen it. Unfortunately, research into MCS has been limited.

'''General direction'''
I wrote this page for MEpedia on the understanding that this would just be a page about MCS--one that wasn't subject to the censorship restrictions of Wikipedia.

While there is a section on how it relates to ME, that certainly wasn't my goal in investing my time in this. My goal was to create
a reputable source that people with MCS could go to for resources and that they could direct others to (ie. loved ones, new friends, doctors, hospitals).

If MEpedia would prefer for the focus to be on how MCS relates to ME, I don't think I'd want to be involved with that. One, because I'm not an expert on that subject (I'm also not sure if much research has been done on that subject); and two, because I don't think it's what people with MCS need.

Sensitivities can be a symptom of ME, but MCS is a standalone condition, and I'd like it to get the space and spotlight it needs as a very serious standalone condition.

If MEpedia isn't the place for that, I understand. I also wish I'd known that before I'd given my content to MEpedia and invested a lot of time on the page. In light of that, I'd like to be able to take my content with me, if you decide to change the direction of the page significantly. I wrote all of it except for the section ME and MCS. It's the culmination of several years work for me, and I'd like to see it published somewhere.

[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 02:55, May 14, 2020 (EDT)Aletheia2020

:::Thanks for your reply [[User:Aletheia2020]]. I perhaps was a bit unclear about how it impacts ME - I think a stand alone page is incredibly useful, but any extra sources that cover it as a comorbidity of ME/CFS and/or fibromyalgia would be really useful. MCS is a huge complication for many with ME so the page is extremely useful. Similarly, the Fibromyalgia has ended up very long, there's a separate [[Fibromyalgia drugs]] page - would a [[Fibromyalgia treatments]] summary page be helpful? Anything that could be added to individual treatment pages about MCS would be helpful, just add a subheading for it (not sure what potions there are in terms of management / treatments).
I think if you have time, some of what is here would be useful on pages like [[Medically unexplained symptoms]], and [[psychologization]]. As regards SEO, the MediaWiki software controls so much of that. Things I've noticed that are very useful are adding some images (quotes or other pictures), careful wording of the first 2 lines of the article, increasing the number of subheadings and having subheadings related to things that are commonly searched for since these then appear as short links in the search results.
Perhaps the "popular culture" heading could be changed to something about what it's like to live with MCS?
Regarding the "learn more" section - are there some leaflets for patients or Consensus guidelines and criteria that could go there?
I've noticed the huge amount of work you are putting into the page, I can't think you enough for that. :-) I see so many online struggling with MCS and with few reliable places to go, and difficulties explaining things to others. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 06:58, May 14, 2020 (EDT)

Thanks for your note and suggestions[[User talk:Notjusttired|talk]] and [[User:JaimeS]].

I took from your further comments that you're OK with leaving the page generally as is but that you wanted the popular culture section changed and more on how MCS impacts ME. Is that right? Or do you still think further sections should be cut, reduced or separated out onto other pages?

As for how MCS impacts ME, I agree it's an important subject, and it's actually not one I had thought much about until this conversation.

Myself I have both conditions, and I would say that out of the people I know with severe and longstanding MCS, the majority seem to also have ME.

From my perspective, the biggest complication MCS creates for a person who also has ME is access/disability issues, which can greatly compromise getting accommodation, support and medical care. Of course, these disability aspects of MCS create these complexities for the sufferer in relation to any comorbid medical condition, not just ME. It complicates them getting medical care for MCS symptoms.

Access issues is a section I've been meaning to write (and it's alluded to in hospital care). I've been procrastinating on it cos it's literally such a big subject, I'm still figuring out how to summarise it into a small section.

So, im summary, I agree that this subject is important. It's just not what I had in mind when I wrote this page page. And to me it seems a bit specific for this page.

I wrote this page with a general, unninformed target audience in mind, hence talking a little about a wide range of subjects, with the idea that the reader could come to the page with literally no idea what MCS is.

In contrast, how MCS impacts ME would be for an informed audience (ie. mostly likely people with both conditions or their loved ones or carers).

As for SEO, the reason I started paying more attention to that, is that when the page was first up (for the first month or so), it was coming up around page 30 on Google--really too deeply buried to make a difference for random searches. I consulted an SEO expert and he suggested incorporating certain words and questions into the content, where possible. Two weeks after I started doing that, I noticed the page coming up much higher in Google for certain subjects. And it seemed to come up higher still the more I did it. It wasn't the only SEO tactic I used, so I don't know for sure whether it was responsible for it coming up higher, but I think it might have been.

Like you [[User talk:Notjusttired|talk]] the SEO consultant said that incorporating common googled phrases and questions in headings is the best, although I thought your page followed a similar template to Wikipedia in relation to headings, so didn't want to mess with them. It sounds like there is some flexibility there, though?

On images [[User talk:Notjusttired|talk]], thanks, that's good to know. They would be good to incorporate. Is there a place that MEpedia contributors commonly get stock images?

And [[User:JaimeS]] with the Safe review having non-scientific resources quoted, I assumed this was OK because a movie review is a movie review--ie. it's not making any controversial scientific claims (and obviously there are no scientific sources about movies). I still thought there was value in quoting media and academic sources about the film because it gives a glimpse into the director's intent and how it was widely interpreted.

I see that Safe has been shortened and some of that content moved to the Safe page. Wasn't sure if that related to the sources I'd used to you just wanting to shorten it.

But I wonder if you'd consider leaving it as is. I ask because the review was carefully written, dense with terms and phrases that I thought could potentially help SEO. It was easier to do that in this section because it had freer form that the scientific sections.

As well, I think the detail about Safe is important because it's not a straight-out narrative about someone having MCS.

The film is actually very vague about what's happening to Carol and why (even though it's a perfectly realistic depiction of what MCS looks like). This vagueness is probably why the film was interpreted in many diverse ways (eg. as a horror film, as a feminist film).

The summary as brief as it is now I don't think really conveys the nuance of how nuance of how the condition is presented. For example, I think it's an important detail to include that nowhere in the film does it mention MCS. It's just that Haynes has confirmed that this was the condition he wrote the film about. Haynes actually wrote the film as a metaphor for how patients with AIDS were treated. I didn't go into that cos it did seem like unnecessary detail for the MCS page, but, basically, Safe isn't a clear cut film about MCS.

Also, I thought because it is at the bottom of the page, I didn't think it would distract from other content by being a little detailed.

Finally re Mepedia policies, apologies if I haven't adhered to all of them and for the time it takes other editors to fix my mistakes [[User:JaimeS]] [[User talk:Notjusttired|talk]]. I did read through them at the start, and probably didn't retain all I read. I'll go over them again. But my memory isn't great, so thanks for nudges about times that I've deviated from them. [[User:Aletheia2020]]

Hello all, I am just coming up to speed on the discussion and I am very impressed with what, mainly, [[User:Aletheia2020]] has put together here. The MCS page has taken on a life of its own, and I think that Mepedia in general has grown into something far beyond what the founders originally envisioned. I actually found this page because I was appalled at the bias on wikipedia's MCS page. I used to donate to Wikipedia, but my donations will be going to Mepedia instead, now.

====Re: Re: Popular culture -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 19:29, May 16, 2020 (EDT)====

:: Replace this text with your reply

====Re: Re: Popular culture -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 00:07, September 26, 2021 (UTC)====

:: Replace this text with your reply

===Re: Popular culture -- [[User:JaimeS|JaimeS]] ([[User talk:JaimeS|talk]]) 13:13, May 15, 2020 (EDT)===

: I agree that the section that exists now is a little over-sourced and could be edited down. Re: censorship, I know that Wikipedia has a really frustrating and demeaning history of falling on the side of reactionary skepticism/mockery of people with chronic conditions. MEpedia is moderated by a patient advocacy organization, not would not seek stifle the voice of people with chronic conditions.

I think you and I have had conversations on this, Aletheia2020! You know I agree with you that good information should be available for those who seek it. As I mentioned when we spoke about this, we do have particular requirements for which sources are considered scholarly, and some general editing rules of thumb (like how many sources are cited per fact). You can find most of these in the science guidelines (http://me-pedia.org/wiki/Science_Guidelines).

Since this is a Wiki, the page would be open to improvement by anyone at any time. In the case of vandalism or unhelpful edits, we have the ability to revert to the previous edits, but locking a page indefinitely after one set of edits would be something we would only do if we were seeing (or suspected we would see) repeated vandalism on the page.

[Edit -- reading quickly through, let me know if there's anything I've missed.]

== Missing reference #19 -- [[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 23:52, February 9, 2020 (EST) ==

[[User:Aletheia2020]] Thanks for your great work on this page! There is one reference missing though, currently numbered #19. Please double-check. Thanks again.
<br>[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 23:52, February 9, 2020 (EST)

:[[User:Pyrrhus]] Thank you, and sorry about that reference. For some reason, a few disappeared. It will take me a bit of time to work out which ones went missing when I cut and pasted. I'll try to fix it in the coming days <br>[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]])

== First section on chemical sensitivities in ME/CFS ==

Hey, I wasn't sure who edited this section, but I envisaged this page as one about MCS as a standalone condition--a condition which is commonly comorbid with ME/CFS. I didn't want it to be chemical sensitivities or MCS in ME/CFS, since the content that follows that section isn't that.

I was going to change it back, but if you don't agree, happy to chat about it.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:17, February 12, 2020 (EST)Aletheia2020

:I'm afraid I don't understand what exactly you are referring to. Could you clarify? Generally speaking, pages on MEpedia should state at the outset what the relevance to ME/CFS is. This section is usually titled "Such-and-such in ME/CFS". The point of the section is to explain why this topic is RELEVANT to ME, to avoid having the page deleted for falling outside the scope of MEpedia. The merits of considering a particular condition as a COMORBIDITY are typically covered in a separate section. I hope this helps.
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 20:51, February 10, 2020 (EST)

::Hey [[User:Pyrrhus]] thank you for the extra details. I understand.

::My concerns is that medication, food and odour sensitivities are not MCS and the way that the paragraph is now phrased makes it a little confusing on a page about MCS--especially when it's the first section after the intro.

::MCS has specific diagnostic criteria, and, yes, it often is accompanied by medication, food and odour sensitivities, but not always. And the MCS community has some good reasons to distinguish between odour and chemical sensitivities because different studies and conclusions apply to these two phenomenon.

::If you'd rather leave the title like that because its your convention, no worries. I think that works OK.

::But I think that taking the paragraph back to what I had would make it clearer about what MCS is. Food sensitivities etc are really for a whole nother page.

::Also, I spelled out ME/CFS here since it's the first time it's mentioned on the page and people may come to this page from Googling MCS and not know what ME/CFS is. I also thought it important to specify that the consensus documents were about ME/CFS since it's not clear otherwise what they are consenses about.

::What do you think?[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:17, February 12, 2020 (EST)Aletheia2020

:::You make some very good points [[User:Aletheia2020]]. Give me a little time to incorporate your points into a draft section, which I will post here on the discussion page for you to review and edit. Thanks.
:::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:41, February 12, 2020 (EST)

:::Okay, [[User:Aletheia2020|Aletheia2020]], how does the following section look?
:::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 20:59, February 12, 2020 (EST)

::::Thanks for doing that [[User:Pyrrhus|Pyrrhus]]. Looks good. I think that that is very clear. Whether that level of detail is required above what was there before, I don't know. But I found it interesting to read the details.

::::The only thing I didn't agree with was the last bit, saying some studies differentiate odour and chemical sensitivities. I think it's a very important to make clear that MCS is not odour sensitivity. I think this is a common misconception.

::::If you look at the 1999 criteria for MCS (and proposed changes to that in the 2019 consensus) there is nothing about sensitivities to odours mentioned in the diagnostic criteria.

::::Some triggering chemicals have odours and some people with MCS have exaggerated senses of smell, but many triggering chemicals (eg. many pesticides) don't have a perceptible smell and many people with MCS have normal senses of smell, and some have no sense of smell at all (which makes avoiding triggers pretty tricky).

::::In my experience, studies into odour sensitivity are often more focused on a perceived nocebo/psychosomatic angle, and in relation to MCS, these have been used in attempts to discredit MCS as a physical disorder. So I'd rather keep my distance from them.

::::From what I can tell, the Quackwatch/SBM mob like to characterise MCS as something like: a bunch of hysterical women getting anxious, angry and upset when they smell perfume or petrol, in some kind of paranoid fit of chemophobia.

::::But this characterisation doesn't explain MCS when the triggering chemical has no smell or when the reaction is from topical contact, ingestion or injection (eg. in the case of anaesthetics, which are notorious for making people with MCS ill).

::::Anyway, in summary, I'd just cut the final sentence. I think the rest of the contact makes it clear MCS is not sensitivity to odours. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

:::::Thanks for all the background, [[User:Aletheia2020|Aletheia2020]]. I have learned a lot about MCS in this conversation. I think many people in the ME community, including those with MCS, are unaware that MCS has specific diagnostic criteria. So your work on this page helps a lot. I'll go ahead and cut the final sentence and then copy it over. Thanks again.
:::::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:17, February 14, 2020 (EST)

::::::It's really good to read that feedback : [[User:Pyrrhus|Pyrrhus]] -- thank you. I think the "is MCS real?" conversation has really eclipsed conversations about what the condition actually is. And that hasn't helped sufferers. Hopefully this page is of use to other people with chemical sensitivities or MCS.

::::::Also, thank you also for your patience with me as I've been learning how things work on here.````Aletheia2020

<div style="background:#FFFFE0;border:1px dotted black">
== MCS in ME and ME/CFS ==
MCS has been described as a comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) and [[fibromyalgia]].<ref>{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref>{{Cite news|url=https://www.verywellhealth.com/fibromyalgia-comorbid-overlapping-conditions-716184|title=Illness That Come Along with Fibromyalgia & Chronic Fatigue Syndrome|last=Dellwo|first=Adrienne|authorlink=Adrienne Dellwo|date=Feb 26, 2018|work=Verywell Health|access-date=2018-08-23|archive-url=|archive-date=|url-status=}}</ref> The [[Canadian Consensus Criteria]] for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and lists "Multiple Chemical Sensitivities (MCS)" as a comorbidity. The [[International Consensus Criteria]] for diagnosing myalgic encephalomyelitis (ME) lists "sensitivities to food, medications, odours or chemicals" as a symptom and lists "multiple chemical sensitivities" as a comorbidity. A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and lists "Multiple Chemical Sensitivities" as a commonly comorbid condition.<ref>“Diagnosing and Treating ME/CFS” by the U.S. ME/CFS Clinician Coalition, August 2019. https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view</ref>

However, it is important to note that MCS has specific diagnostic criteria which do ''not'' include medication, food or odor sensitivities.<ref name="pmid10444033" /> Furthermore, some studies have differentiated odor sensitivity and chemical sensitivity as two separate phenomena.{{citation needed}}
</div>

== On This is a Potential comorbidities page ==
I wondered how we can resolve whether it is or isn't a comorbidity. I know the US Coalition on ME/CFS consensus from last year said it was, but I'm really not up on other ME/CFS stuff.

I think removing the banner would look better if it can be agreed either way.

Thanks <br>[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]])

:A page is expected to objectively weigh the evidence for and against considering a condition as a comorbidity. As much as possible, we leave it up to the reader to draw their own conclusions. Because of this, we recently renamed our "Comorbidities" category to "Potential comorbidities", in order to let the page itself weigh the evidence, and in order to let the reader come to their own conclusion.

::[[User:Pyrrhus]] OK, got it. Thanks [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

:These sorts of debates just don't belong in category-naming decisions. Categories are simply a convenient way to group articles, nothing more, and we don't want to complicate things by politicizing category names. We did the same thing with the "Treatments" category, which is now called "Potential treatments". With that said, the banner is indeed ugly and distracting. We have developed a better banner and are (still) waiting for our technical people to finally implement the better banner. For the time being, we just have to put up with the current ugly and distracting banner...

::[[User:Pyrrhus]] OK. That's good to know. Yes, it's very dominating as it is atm. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

:Hope this helps. Please let me know if you have any further questions.
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:07, February 10, 2020 (EST)

::Oops, [[User:Aletheia2020]], I forgot to mention that the word "comorbidity" on MEpedia has a specific meaning: it means a condition that is statistically more likely to be found in the original condition, than it is to be found in the general population. I only mention that since there are other definitions out there...
::[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 21:28, February 10, 2020 (EST)

::::[[User:Pyrrhus]] OK, noted. I'll stick with your definition. [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:26, February 12, 2020 (EST)Aletheia2020

== English or American spelling? ==

[[User:Pyrrhus]] I noticed that you changed some ss to zs in words but changed centers to centres. So I was unsure if you went with American or English spelling on this page? Thanks [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 03:44, February 12, 2020 (EST)Aletheia2020

:The [[MEpedia:Manual of style]] specifies American spelling and dates, which I why I changed some spelling, including changing "centres" to "centers". Then I realized that the word "centres" was part of a quote from a Canadian, so I changed "centers" back to "centres". I hope this clarifies things. Good catch!
:[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:48, February 12, 2020 (EST)

::Ah, I got it [[User:pyrrhus|pyrrhus]]. No worries.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

== Questionable comparison that could be interpreted as bias ==

[[User:Aletheia2020|Aletheia2020]], I notice that you make a comparison between "merchants of doubt", who are paid to disseminate disinformation that they don't themselves believe, and intolerant skeptics, who may use similar tactics but are unpaid and actually believe what they are claiming. Some may say that this is an unfair comparison that displays bias on our part. Perhaps rephrase?
<br>[[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 14:34, February 12, 2020 (EST)

===Re: Questionable comparison that could be interpreted as bias -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:47, February 12, 2020 (EST)===

: I hear you, and they are good points. But I used the comparison (and think it's important) because Barrett, Gots and Quackwatch have been documented to receive corporate funding.

: As well, I don't think "controversy" as the heading for the section originally labelled "politics" is accurate.

:In my view, the idea that there is a controversy has been manufactured, and I don't want to give it any more oxygen by using a heading that reinforces the idea that there is a heated academic debate going on about MCS being real or not when there isn't.

:In the case of MCS, the views of SBM and Quackwatch are fringe. I also don't consider them genuine skeptics. I know the president of the national association of skeptics, and he thinks SBM is very little to do with skeptic philosophy and a lot to do with pursuing an already-decided agenda. So it's an ideology, not a method for critical thinking.

:No academic review on MCS studies that I've seen has concluded the condition is fake or bogus. Certainly this isn't the conclusion of at least the past five large-scale reviews.

:I called this section politics, to show that there are powerful interests involved, which have influenced the debate and are continuing to influence it (just as we have seen with tobacco, DDT, asbestos and now climate change).

:The most recent large-scale academic review of MCS studies in 2019 (the Italian consensus) even said that the few studies claiming a psychological cause all had clear conflicts of interest and could not be considered reliable on that basis alone (in addition to the methological criticisms levelled at those studies).[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 21:47, February 12, 2020 (EST)Aletheia2020

::Thanks for sharing some of the backstory here. What you describe is perfectly familiar to the ME community. We also have powerful interests who prominently claim that ME is a fake disease, receive funding from insurance companies to give speeches to doctor conventions "informing" them that ME is a fake disease, are paid by the insurance companies to testify at disability pension hearings to deny disability payments to ME patients, who then have no choice but to commit suicide.

::These powerful interests have even gone so far as to set up their own academic journals to publish their "peer-reviewed" work, and have set up their own media organization to plant stories in various newspapers claiming that bedridden ME patients are plotting to assassinate innocent scientists. (not a joke)

::Yes, it's immensely frustrating that, in these days, anyone can manufacture a controversy simply by stating that a controversy exists. If we were a public relations organization, we would gladly ignore all manufactured controversies. But we're an encyclopedia, and we have a duty to objectively report on all controversy, regardless of the controversy's merit (or lack thereof).

::MEpedia's editorial guidelines (see [[MEpedia:POV]]) state that section headings describing controversies can be titled "Controversy" or "Criticism". I chose the word "Controversy" because "Criticism" implies legitimate criticism, but the word "Controversy" does not.

::And I don't think you have to worry about readers equating skepticism with critical thinking. The common use of the word "skeptic" is just someone who doubts something. (like a "climate skeptic" who doubts climate change) But if you fear readers may use a more nuanced definition of "skeptic", you can just refer to them as "critics" or "bloggers" instead of as "skeptics".

::Hope this helps. [[User:Pyrrhus|Pyrrhus]] ([[User talk:Pyrrhus|talk]]) 13:28, February 13, 2020 (EST)

::[[User:pyrrhus|pyrrhus]] OK. I understand. Thanks. And, yes, you're probably right that most people don't know much about the divisions in skeptic movements.[[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 01:29, February 14, 2020 (EST)Aletheia2020

==References==
{{reftalk}}

== Headings and SEO -- ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT) ==

Please avoid using questions as headings, and avoid using the page name within headings. The MediaWiki software is built by Wikipedia so should already be able to work out that a subheading is linked to the topic page, and phrasing the first line under the heading carefully should be enough, e.g. The symptoms of MCS include...". Headings should be worded as per the examples on [[MEpedia:Article outlines]].

SEO rankings increase when small pages cover the exact topic, e.g. you could create a few small page in the format of a '''list''', [[Multiple chemical sensitivity symptoms]] then use <code><nowiki >{{See also|Multiple chemical sensitivity}}</nowiki></code> to point back to the original page. The original page would a less detailed description of symptoms, and could use <nowiki >{{See also|Multiple chemical sensitivity symptoms}}</nowiki></code> to take users back to it. The new page would go in the [[Category:Lists]] and [[Category:Signs and symptoms]]. I am thinking of creating a list page for [[Deaths from myalgic encephalomyelitis/chronic fatigue syndrome]], so will be interested to see how this ranks compared to the [[causes of death]], [[Sophia Mirza]], and [[severe and very severe ME]] pages. (Sophia's is one of the top pages on MEpedia). ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT)

==Images==
I believe images would help SEO. If you would like a simple image creating eg for the symptoms, can you let me know what design and colors (green? primary colors?) you would like or links to any images with the layout you want. Images are highlighted by search engine results and encourage views and also get saved to pinterest which results in more views. ~[[User:Notjusttired|Njt]] ([[User talk:Notjusttired|talk]]) 12:13, June 30, 2020 (EDT)

== Additions to history -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 05:54, September 23, 2021 (UTC) ==

It could aid patient advocacy to put some precedent setting decisions in here. One court case example that comes to mind is the Canada Revenue Association vs a woman (a large MCS advocate in Canada, forget the name) who had claimed tax deductible renovations on her home to accommodate MCS. Would this be helpful here, or would a section on MCS in the court system be more suitable?

== MCS as a symptom of a disease, not a disease. -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 06:02, September 23, 2021 (UTC) ==

This is a controversial idea, I know, and I am not aiming to make any additions or changes. However, given the rapidly advancing state of knowledge on the underlying mechanisms of MCS, I think it will be helpful to have a discussion about this idea.

The more I learn about MCS and talk to people with it, the more it becomes apparent that the sensitivity is a symptom of underlying problems which are diverse, complex, and different for every individual. And yes, the underlying problems are almost universally caused or initiated by toxic exposure. One example is Mast Cell Activation Syndrome. Another is Oxidative Stress. You get the idea. Thoughts?

===Re: MCS as a symptom of a disease, not a disease. -- [[User:Aletheia2020|Aletheia2020]] ([[User talk:Aletheia2020|talk]]) 08:12, February 21, 2022 (UTC)===

I agree with you. I think MCS is a sensitivity syndrome that likely has different causes in different people.

But I also think that for recognition purposes (eg. access policies) having it defined as a condition (even if that only means an array of symptoms provoked in particular ways) may be helpful.

Are you suggesting talking about this specifically or just changing reference words

== Additions to recognition section -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:02, September 23, 2021 (UTC) -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:02, September 23, 2021 (UTC) ==

It would be helpful for patients to add some more detail on legal recognition. For example, the Canadian Human Rights Commission has taken a rather firm stance on environmental sensitivities: https://www.chrc-ccdp.gc.ca/sites/default/files/policy_sensitivity_0.pdf

"Individuals with environmental sensitivities experience a variety of adverse reactions to environmental
agents at concentrations well below those that might affect the “average person”. This medical condition is a
disability and those living with environmental sensitivities are entitled to the protection of the Canadian
Human Rights Act, which prohibits discrimination on the basis of disability."

== New references for notable studies section -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 16:38, September 23, 2021 (UTC) ==

A recent review paper, published in reviews on environmental health about a week ago, would be useful to have in this section:

https://www.degruyter.com/document/doi/10.1515/reveh-2021-0043/html

== What's in a name? Adding synonyms to the introductory sentence and redirect pages -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 22:53, October 1, 2021 (UTC) ==

MCS is known by many names, depending on the legal context and jurisdiction. For example, The Canadian Human rights commission likes to call it "environmental sensitivity" although this is a more broad umbrella term. Another term being used in pathophysiological literature is TILT. Some more examples:

Environmental illness
Chemical intolerance
Gulf War syndrome
Sick building syndrome

Or perhaps we should remove IEI from the first sentence altogether and have a section dedicated specifically to alternate names?

Thoughts?

===Re: What's in a name? Adding synonyms to the introductory sentence and stub pages -- [[User:Silliestchris|Silliestchris]] ([[User talk:Silliestchris|talk]]) 22:54, October 1, 2021 (UTC)===

: Replace this text with your reply

User talk:Silliestchris

2022-02-21T08:08:39Z

Aletheia2020:Thank you and welcome

{{Template:Welcome|realName=|name=Silliestchris}}

-- [[User:Silliestchris|Silliestchris message]] ([[User talk:Silliestchris message|talk]]) 05:25, September 23, 2021 (UTC)

Hi and thanks so much for the msg. Apologies--I haven't been on MEpedia for a while.

I'd be so grateful for your input, particularly when, from what I've read, Canada seems many eons ahead of Australia (where I'm from), on policies for sensitive people.

I'm unsure when I'll have the time to look at suggestions atm but, if you haven't already, you could apply to access the page as an editor by contacting them MEpedia team.

Also, if you wanted to chat in a more informal way about the content of this page, I'd be happy to (maybe on Whatsapp or Telegram).

Aletheia2020

User talk:Silliestchris

2022-02-21T08:06:33Z

Aletheia2020:Thank you and welcome

{{Template:Welcome|realName=|name=Silliestchris}}

-- [[User:New user message|New user message]] ([[User talk:New user message|talk]]) 05:25, September 23, 2021 (UTC)

Hi and thanks so much for the msg. Apologies--I haven't been on MEpedia for a while.

I'd be so grateful for your input, particularly when, from what I've read, Canada seems many eons ahead of Australia (where I'm from), on policies for sensitive people.

I'm unsure when I'll have the time to look at suggestions atm but, if you haven't already, you could apply to access the page as an editor by contacting them MEpedia team.

Also, if you wanted to chat in a more informal way about the content of this page, I'd be happy to (maybe on Whatsapp or Telegram).

Multiple chemical sensitivity

2021-07-14T07:10:54Z

Aletheia2020:Fixed references

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name=":0" /><ref name=":1">Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy 2020 Prepared by Dr Sharyn Martin September 2020, p.2</ref><ref name=":2" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name=":5">[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.12</ref>

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name=":0">{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name=":1" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name=":2">{{Cite journal|last=Gibson|first=Pamela|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2016/01/01|title=A Review of the Life Impacts of Environmental Sensitivities|url=|journal=Internal Medicine Review|volume=|issue=May|pages=p.9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* mould
* carpet
* fumes from paint
* pesticide residue
* fumes from [nearby] laundry facilities
* fumes from cleaning products in common areas and
* cigarette smoke.<ref name=":3" />
People with MCS suffer as a result of their lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name=":11" /> The inquiry concluded that in society at large, there was little recognition of how serious and severe environmental illness could be and that there was "a discouraging shortage of services and supports" for people living with conditions like MCS.<ref name=":11" /> It also found that people with environmental illness commonly experienced stigma, including from landlords, who were "often skeptical about the severity and impact of their conditions.”<ref name=":11">[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. pp. 7, 12, 19. </ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-07-12T08:59:16Z

Aletheia2020:/* Accommodation */ formatting

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name=":0" /><ref name=":1">Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy 2020 Prepared by Dr Sharyn Martin September 2020, p.2</ref><ref name=":2" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name=":5">[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.12</ref>

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name=":0">{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name=":1" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name=":2">{{Cite journal|last=Gibson|first=Pamela|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2016/01/01|title=A Review of the Life Impacts of Environmental Sensitivities|url=|journal=Internal Medicine Review|volume=|issue=May|pages=p.9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing".<ref name=":3" /> Some of these included:
* mould
* carpet
* fumes from paint
* pesticide residue
* fumes from [neaby] laundry facilities
* fumes from cleaning products in common areas and
* cigarette smoke.<ref name=":3" />
People with environmental illnesses (including MCS) suffer as a result of a lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name=":5" /> The inquiry said "in society at large, there is little recognition of how serious and severe these conditions are", and that there is "a discouraging shortage of services and supports for people living with these conditions."<ref>[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.12</ref> It also said people with environmental illnesses commonly experienced stigma, including from landlords, who were " often skeptical about the severity and impact of their conditions.”<ref>[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.19</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-07-12T08:45:55Z

Aletheia2020:/* Accommodation */ new content

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
People with MCS commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a systemic problem for those with the condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name=":0" /><ref name=":1">Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy 2020 Prepared by Dr Sharyn Martin September 2020, p.2</ref><ref name=":2" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref><ref name=":5">[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.12</ref>

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name=":0">{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name=":1" />

A 2016 academic review about the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult [for them] to find or maintain housing that does not exacerbate the condition." It also said two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition at some period of their illness.<ref name=":2">{{Cite journal|last=Gibson|first=Pamela|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2016/01/01|title=A Review of the Life Impacts of Environmental Sensitivities|url=|journal=Internal Medicine Review|volume=|issue=May|pages=p.9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing" (Some of these included carpet, strong fumes from laundry products and cleaning products in common areas, and mould and cigarette smoke).<ref name=":3" />

People with environmental illnesses (including MCS) suffer as a result of a lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada.<ref name=":5" /> The inquiry said "in society at large, there is little recognition of how serious and severe these conditions are" and that there is "a discouraging shortage of services and supports for people living with these conditions."<ref>[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.12</ref> It also said people with environmental illnesses commly experienced stigma, including from landlords, who were " often skeptical about the severity and impact of their conditions.”<ref>[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. p.19</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-07-12T07:41:42Z

Aletheia2020:Added more content on housing

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
People with chemical sensitivities commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a common problem for those with the condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name=":0" /><ref name=":1">Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy 2020 Prepared by Dr Sharyn Martin September 2020, p.2</ref><ref name=":2" /><ref name=":3">[https://archdisabilitylaw.ca/resource/paper-the-legal-rights-and-challenges-faced-by-persons-with-chronic-disability-triggered-by-environmental-factors/ The Legal Rights and Challenges Faced by Persons with Chronic Disability Triggered by Environmental Factors.] Report prepared by ARCH Disability Law Centre and the Canadian Environmental Law Association. September 2019</ref>

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name=":0">{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
While a 2019 survey in Australia found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name=":1" />

A 2016 academic review on the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult to find or maintain housing that does not exacerbate the condition." It also said around two-thirds of people with environmental sensitivities had reported having had to live in "unusual circumstances" as a result of their condition, at some period of their illness.<ref name=":2">{{Cite journal|last=Gibson|first=Pamela|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2016/01/01|title=A Review of the Life Impacts of Environmental Sensitivities|url=|journal=Internal Medicine Review|volume=|issue=May|pages=p.9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

A 2019 report from Canada about human rights' issues faced by people with environmental illness said: “In focus groups, participants with environmental health disabilities voiced significant concerns about the barriers they experience in finding and maintaining accessible and affordable rental housing." Some of the barriers mentioned included carpet, strong fumes from laundry products and cleaning products in common areas, and mould and cigarette smoke.<ref name=":3" />

People with chemical and environmental sensitivities suffer as a result of a lack of access to safe housing, according to a 2018 government inquiry from Ontario, Canada. The inquiry concluded that "in society at large, there is little recognition of how serious and severe these conditions are" and that there is "a discouraging shortage of services and supports for people living with these conditions." It said people with environmental illnesses experienced stigma in many non-medical contexts, including from landlords who were " often skeptical about the severity and impact of their conditions.”<ref>[https://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2018/task_force_on_environmental_health_report_2018.pdf An Action Plan to Improve Care for People with Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS), Fibromyalgia (FM) and Environmental Sensitivities/Multiple Chemical Sensitivity (ES/MCS)] Final Report of the Task Force on Environmental Health, Ottawa. Canada. December, 2018. pp.12, 7, 19</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-07-12T07:09:58Z

Aletheia2020:Some additions to accommodation

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
People with chemical sensitivities commonly encounter difficulties finding housing that is suitable and accessible for their condition; and as a result, homelessness is a common problem for those with the condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name=":0" /><ref name=":1">Australian National Register of Environmental Sensitivities Submission to a New National Disability Strategy 2020 Prepared by Dr Sharyn Martin September 2020, p.2</ref>

A 2002 housing survey of people with MCS in the United States found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref name=":0">{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>
While a 2020 report from Australia said that a 2019 survey found that 55.2% of respondents with chemical sensitivities reported suffering hardship accessing safe and affordable housing.<ref name=":1" />

A 2016 academic review on the psychosocial impacts of environmental sensitivities found that “as persons acquire sensitivities, it becomes more and more difficult to find or maintain housing that does not exacerbate the condition." It also said around two-thirds of people with environmental sensitivities had reported having live in "unusual circumstances" as a result of their condition, at some period of their illness.<ref>{{Cite journal|last=Gibson|first=Pamela|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2016/01/01|title=A Review of the Life Impacts of Environmental Sensitivities|url=|journal=Internal Medicine Review|volume=|issue=May|pages=p.9|doi=10.18103/imr.v0i2.63|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-06-17T08:30:51Z

Aletheia2020:formatting

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
Chemically sensitive people typically encounter difficulties finding suitable housing and homelessness is a common problem for people with this condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref> A 2002 housing survey of people with chemical sensitivities found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref>{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult horror film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-06-16T07:47:59Z

Aletheia2020:/* Safe (1995) */ format

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
Chemically sensitive people typically encounter difficulties finding suitable housing and homelessness is a common problem for people with this condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref> A 2002 housing survey of people with chemical sensitivities found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref>{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" /> Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-06-16T07:46:09Z

Aletheia2020:Grammar and format only

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
Chemically sensitive people typically encounter difficulties finding suitable housing and homelessness is a common problem for people with this condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref> A 2002 housing survey of people with chemical sensitivities found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref>{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

It tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home.

With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" /> Early in the Covid-pandemic, Carol's isolation was compared to the psychosocial experience of lockdowns.

{{See also||||||}}<div role="note" class="hatnote navigation-not-searchable">{{See also|Safe}}</div>

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-05-24T05:08:35Z

Aletheia2020:Added small section on long-haul covid and mcs

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
Chemically sensitive people typically encounter difficulties finding suitable housing and homelessness is a common problem for people with this condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref> A 2002 housing survey of people with chemical sensitivities found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref>{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Does COVID-19 cause multiple chemical sensitivity? ==
There have been anecdotal reports of people with long-haul COVID, or chronic COVID, developing fragrance and other chemical sensitivities.<ref>{{Cite web|url=https://www.verywellhealth.com/long-term-covid-19-severe-fragrance-allergies-5087489|title="Why Are COVID-19 Long-Haulers Developing Fragrance Allergies?"|last=Fahmy|first=Asmae|authorlink=|last2=|first2=|authorlink2=|date=13 November 2020.|website=Verywellhealth.com|archive-url=|archive-date=24 May 2020|url-status=|access-date=}}</ref>

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

''Safe'' tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home. With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Corona virus pandemic, Carol's social isolation was compared to the psychosocial experiences of Covid-19 lockdowns<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.{{See also|Safe}}<div role="note" class="hatnote navigation-not-searchable">{{See also|Safe}}</div>

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]

Multiple chemical sensitivity

2021-05-24T04:56:22Z

Aletheia2020:Edits to access

'''Multiple chemical sensitivity''' ('''MCS'''), also known as '''idiopathic environmental intolerances''' ('''IEI'''), is an acquired, chronic, multi-system illness, in which people experience a range of symptoms in response to exposure to certain everyday chemicals.

A 2018 scientific review said MCS was "a complex syndrome that manifests as a result of exposure to a low level of various common contaminants."<ref name="Rossi2018">{{Cite journal|last=Rossi|first=Sabrina|author-link=|last2=Pitidis|first2=Alessio|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Feb 2018|title=Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=2|pages=138–146|doi=10.1097/JOM.0000000000001215|issn=1076-2752|pmc=5794238|pmid=29111991|access-date=|quote=...some countries, such as Germany and Austria, and some agencies and provisions in the United States, such as the Environmental protection Agency (EPA) and the American Disability Act (ADA), have recognized this pathology.|via=}}</ref>

While a 2019 consensus paper on MCS defined the condition as an "acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arise in response to a demonstrable exposure to chemicals," even at doses much lower than would cause a reaction in the general population.<ref name="Ch2">{{citation|chapter=2. Epidemiologia|trans-chapter=2. Epidemiology|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Common triggers for MCS symptoms include [[pesticide]]s, fragranced products, petrochemicals, [[formaldehyde]] and mold.<ref name="Ch1">{{cite book|chapter=1. Sensibilitá Chimica Multipla (MCS): Definizione di Caso|trans-chapter=1. Clinical features of the disease|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref name=":9">{{citation|chapter=1.2 Scatenamento della MCS|trans-chapter=1.2 Triggering of MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>
==What are the symptoms of multiple chemical sensitivity? ==
There is a consensus that the symptoms of MCS affect multiple organs and body systems,<ref name="Ch1" /><ref name="pmid10444033">{{cite journal|year=1999|title=Multiple chemical sensitivity: a 1999 consensus|journal=Arch. Environ. Health|volume=54|issue=3|pages=147–9|doi=10.1080/00039899909602251|pmid=10444033|url=https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f}}</ref><ref name="pmid30088144" /><ref name=":6" /> range from mild to disabling<ref name="Ch1" /><ref name=":6" /><ref name=":7">{{Citation|last=Task Force on Environmental Health|date=2017|url=http://www.health.gov.on.ca/en/common/ministry/publications/reports/environmental_health_2017/task_force_on_environmental_health_report.pdf|title=Time for leadership: recognizing and improving care for those with ME/CFS, FM and ES/MCS. Phase 1 report. |location=Toronto, Ontario|publisher=Ministry of Health and Long-Term Care}}</ref> and decrease quality of life.<ref name="pmid30088144" /><ref name="Steinemann2018">{{Cite journal|last=Steinemann|first=Anne|author-link=|last2=|first2=|author-link2=|date=Mar 2018|title=National Prevalence and Effects of Multiple Chemical Sensitivities|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5865484/|journal=Journal of Occupational and Environmental Medicine|volume=60|issue=3|pages=e152–e156|doi=10.1097/JOM.0000000000001272|issn=1076-2752|pmc=5865484|pmid=29329146|access-date=|quote=|via=}}</ref><ref name=":7" /><ref>{{Cite journal|last=Loria-Kohen|first=Viviana|last2=Marcos-Pasero|first2=Helena|last3=de la Iglesia|first3=Rocío|last4=Aguilar-Aguilar|first4=Elena|last5=Espinosa-Salinas|first5=Isabel|last6=Herranz|first6=Jesús|last7=Ramírez de Molina|first7=Ana|last8=Reglero|first8=Guillermo|date=2017-08-22|title=Multiple chemical sensitivity: Genotypic characterization, nutritional status and quality of life in 52 patients|url=https://www.ncbi.nlm.nih.gov/pubmed/28283271|journal=Medicina Clinica|volume=149|issue=4|pages=141–146|doi=10.1016/j.medcli.2017.01.022|issn=1578-8989|pmid=28283271}}</ref><ref>{{Cite journal|last=Gibson|first=Pamela Reed|last2=Leaf|first2=Britney|last3=Komisarcik|first3=Victoria|date=2016-01-12|title=Unmet medical care needs in persons with multiple chemical sensitivity: A grounded theory of contested illness|url=http://www.sciedupress.com/journal/index.php/jnep/article/view/8165|journal=Journal of Nursing Education and Practice|language=en|volume=6|issue=5|pages=75|doi=10.5430/jnep.v6n5p75|issn=1925-4059}}</ref><ref>{{Cite journal|last=García-Sierra|first=Rosa|last2=Álvarez-Moleiro|first2=María|date=2014-07-01|title=Evaluation of suffering in individuals with multiple chemical sensitivity|url=http://www.sciencedirect.com/science/article/pii/S1130527414000073|journal=Clínica y Salud|language=en|volume=25|issue=2|pages=95–103|doi=10.1016/j.clysa.2014.06.006|issn=1130-5274}}</ref><ref>{{Cite journal|last=Alobid|first=Isam|last2=Nogué|first2=Santiago|last3=Izquierdo-Dominguez|first3=Adriana|last4=Centellas|first4=Silvia|last5=Bernal-Sprekelsen|first5=Manuel|last6=Mullol|first6=Joaquim|date=2014-12-01|title=Multiple chemical sensitivity worsens quality of life and cognitive and sensorial features of sense of smell|url=https://doi.org/10.1007/s00405-014-3015-5|journal=European Archives of Oto-Rhino-Laryngology|language=en|volume=271|issue=12|pages=3203–3208|doi=10.1007/s00405-014-3015-5|issn=1434-4726}}</ref><ref name="Gibson2009">{{Cite journal|last=Gibson|first=PR|author-link=|last2=Vogel|first2=VM|author-link2=|date=Jan 2009|title=Sickness-related dysfunction in persons with self-reported multiple chemical sensitivity at four levels of severity|url=https://onlinelibrary.wiley.com/doi/full/10.1111/j.1365-2702.2008.02439.x|journal=J Clin Nurs.|volume=18|issue=1|pages=72-81|doi=10.1111/j.1365-2702.2008.02439.x|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref>{{Cite journal|last=Koch|first=Lynn|last2=Vierstra|first2=Courtney|last3=Penix|first3=Ken|date=2006-09-01|title=A Qualitative Investigation of the Psychosocial Impact of Multiple Chemical Sensitivity|url=https://connect.springerpub.com/content|journal=Journal of Applied Rehabilitation Counseling|language=en|volume=37|issue=3|pages=33–40|doi=10.1891/0047-2220.37.3.33|issn=0047-2220}}</ref>

Symptoms of MCS include [[headache]], [[migraine]], neurocognitive deficits, dizziness, fatigue, cardiac arrhythmia, tachycardia, [[hypotension]], hypertension, [[:Category:Digestive signs and symptoms|gastrointestinal problems]], [[nausea]], [[vomiting]], muscle and joint pain, skin rashes, hives, [[visual dysfunction|visual disturbances]], [[seizure]]s, and [[asthma]].<ref name="Ch1" /><ref name=":6">{{Cite book|at=What is Multiple Chemical Sensitivity|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref><ref name="Valderrama2015" /><ref name=":7" /><ref name="Steinemann2018" /><ref name="Genuis2013">{{cite journal|last1=Genuis|first1=SJ|date=May 2013|title=Chemical sensitivity: pathophysiology or pathopsychology? Is multiple chemical sensitivity a mental illness?|journal=Clinical Therapeutics (Review)|volume=35|issue=5|pages=572–7|doi=10.1016/j.clinthera.2013.04.003|pmid=23642291|url=https://www.ncbi.nlm.nih.gov/pubmed/23642291|last2=Ross|first2=PM|pmc=|quote=The emerging problem of ubiquitous adverse toxicant exposures in modern society has resulted in escalating numbers of individuals developing a CS disorder. As usual in medical history, iconoclastic ideas and emerging evidence regarding novel disease mechanisms, such as the pathogenesis of CS, have been met with controversy, resistance, and sluggish knowledge translation.|last3=Whysner|first3=J|last4=Covello|first4=VT|last5=Kuschner|first5=M|last6= Rifkind|first6=AB|last7=Sedler|first7=MJ|last8=Trichopoulos|first8=D|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref>{{cite journal|last9=Williams|first9=GM|year=1999|title=Olfaction and Symptoms in the Multiple Chemical Sensitivities Syndrome|url=https://doi.org/10.1006%2Fpmed.1998.0469|journal=Preventive Medicine|volume=28|issue=5|pages=467–480|doi=10.1006/pmed.1998.0469|pmid=10329337}}</ref><ref name="Graveling1999">{{cite journal|vauthors=Graveling RA, Pilkington A, George JP, Butler MP, Tannahill SN|year=1999|title=A review of multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pubmed/10448311|journal=Occupational and Environmental Medicine|volume=56|issue=2|pages=73–85|doi=10.1136/oem.56.2.73|pmc=1757696|pmid=10448311}}</ref> And a 2010 review of MCS research said that the following symptoms, in this order, were the most reported in MCS: [[headache|headache,]] [[fatigue|fatigue,]] confusion, [[depression|depression,]] shortness of breath, [[arthralgia|arthralgia,]] [[myalgia|myalgia,]] [[nausea]], [[dizziness|dizziness,]] [[memory problems|memory problems,]] [[:Category:Digestive signs and symptoms|gastrointestinal symptoms]], respiratory symptoms.<ref name="NICNAS">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2017 review of MCS studies said: “MCS is a syndrome that progresses to increasingly serious stages, with the gradual onset of multiple pathlogies."<ref name="Rossi2018" />[[File:Cosmetics.jpg|thumb|What triggers multiple chemical sensitivity symptoms? Everyday personal care products, particularly fragranced products, are common triggers and their near-ubiquitous use makes many public spaces inaccessible to people with severe sensitivities.<ref name="Grenvillebook">Grenville, Kate. ''The case against fragrance''. Text Publishing. Australia. 2017.</ref> To address this, fragrance-free policies are becoming more common, especially in healthcare settings. The U.S. Centers for Disease Control has been fragrance free since 2009.<ref name="IEQP">{{citation|url =https://www.chemicalsensitivityfoundation.org/pdf/CDC-2009-Indoor-Environmental-Quality-internal-policy542.pdf|title =Indoor Environment Quality Policy|last =Centers for Disease Control Office of Health and Safety|date =2009|location=United States|page=9}}</ref> ]]The following substances are common triggers for adverse symptoms people with MCS:
* pesticides (insecticides and herbicides), biocides and fungicides
* agricultural chemicals, notably [[fertilizer]]s
* [[mold]] and mycotoxins
* synthetic fragrances and products containing fragrance (eg. fragranced deodorant)
* laundry detergents and fabric softeners
* cigarette smoke and woodfire smoke
* petrochemical solvents and plastics
* [[formaldehyde]]
* some building materials
* preservatives, [[food coloring]]s and additives (eg. [[tartrazine]])
* some medications and anesthetics
* air pollution (eg. black carbon, [[nitrogen oxide]], ozone)
* natural [[essential oil]]s.<ref name="Rossi2018" /><ref name="Ch1" /><ref name=":6" /><ref name="pmid10444033" /><ref name="Steinemann2018" /><ref name=":15" /><ref name="Valderrama2015">{{Cite book|last=Valderrama Rodríguez|first=M|last2=Revilla López|first2=MC|last3=Blas Diez|first3=MP|last4=Vázquez Fernández del Pozo|first4=S|last5=Martín Sánchez|first5=Jl|title=Actualización de la Evidencia Científica sobre Sensibilidad Química Múltiple (SQM). |publisher=Ministerio de Sanidad, Servicios Sociales e Igualdad. Instituto Aragonés de Ciencias de la Salud. Informes de Evaluación de Tecnologías Sanitarias (IACS)|date=2015|trans-title=Review of the scientific evidence on Multiple Chemical Sensitivity|url=https://www.sergas.es/Asistencia-sanitaria/Documents/953/Actualizaci%C3%B3n%20de%20la%20evidencia%20cient%C3%ADfica%20sobre%20sensibilidad%20qu%C3%ADmica%20m%C3%BAltiple.pdf}}</ref>{{Rp|17}}<ref name=":49">{{Cite journal|last=Ziem|first=Grace E.|author-link=|date=2018-04-24|title=Multiple Chemical Sensitivity: Treatment and Followup with Avoidance and Control of Chemical Exposures|url=https://journals.sagepub.com/doi/pdf/10.1177/074823379200800409|journal=Toxicology and Industrial Health|language=en|volume=|issue=|pages=|doi=10.1177/074823379200800409|pmc=|pmid=|access-date=|quote=|via=}}</ref><ref name=":50" />

==How is multiple chemical sensitivity diagnosed ==
The 1999 international consensus on MCS is the most common diagnostic criteria for the condition. This consensus was published in ''The Archives of Environmental Health,''<ref name="pmid10444033" /> as the conclusion of a ten-year study by an international multidisciplinary team of 89 clinicians and researchers with different points of view about MCS.<ref name="Ch1" /> They agreed that the clinical characteristics of MCS should be defined as follows:
#a chronic condition,
#with symptoms that recur reproducibly
#in response to low levels of exposure
#to multiple and unrelated chemicals,
#which improve or resolve when triggers are removed, and
#with symptoms which occur in multiple organ systems.<ref name="pmid10444033" /><ref name="Ch1" /><ref name="HooperCh">{{Cite book|title=Psychiatry: An evidence-based text|pages=793-820|isbn=978-1-4441-1326-6|edition=|language=en|title-link=|url=https://books.google.com/books/about/Psychiatry_An_evidence_based_text.html?id=LkbOBQAAQBAJ|access-date=|date=2009-11-27|publisher=CRC Press|last=Hooper|first=Malcolm|author-link=Malcolm Hooper|last2=|first2=|author-link2=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=Puri|editor-first=Bassant|editor1-link=|editor-last2=Treasaden|editor-first2=Ian|chapter=Multiple Chemical Sensitivity|chapter-url=https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf}}</ref>
The [[Quick Environmental Exposure and Sensitivity Inventory]] (QEESI) is a diagnostic tool that is often used to assess a patient for these criteria.<ref name="Ch1" />

Research papers have concluded that knowledge and education about MCS among health professionals is lacking and that this commonly results in delays in the diagnosis and poor management of the condition.<ref name="Gibson2009" /><ref name=":6" /><ref name=":7" />

==ME/CFS and multiple chemical sensitivity==
MCS has been called a common comorbidity of [[ME/CFS|myalgic encephalomyelitis/chronic fatigue syndrome]] (ME/CFS) by several consensus documents:<ref name="ammes-overlapping">{{Cite web|url=https://ammes.org/overlapping-conditions/|title=Overlapping Conditions – American ME and CFS Society|website=ammes.org|language=en-US|access-date=2018-08-12}}</ref><ref name="canadianconsensus-CCC">{{Citation
| last1 = Carruthers | first1 = Bruce M. | authorlink1 = Bruce Carruthers
| last2 = Jain | first2 = Anil Kumar | authorlink2 = Anil Kumar Jain
| last3 = De Meirleir | first3 = Kenny L. | authorlink3 = Kenny De Meirleir
| last4 = Peterson | first4 = Daniel L. | authorlink4 = Daniel Peterson
| last5 = Klimas | first5 = Nancy G. | authorlink5 = Nancy Klimas
| last6 = Lerner | first6 = A. Martin | authorlink6 = Martin Lerner
| last7 = Bested | first7 = Alison C. | authorlink7 = Alison Bested
| last8 = Flor-Henry | first8 = Pierre | authorlink8 = Pierre Flor-Henry
| last9 = Joshi | first9 = Pradip | authorlink9 = Pradip Joshi
| last10 = Powles | first10 = A C Peter | authorlink10 = A C Peter Powles
| last11 = Sherkey | first11 = Jeffrey A. | authorlink11 = Jeffrey Sherkey
| last12 = van de Sande | first12 = Marjorie I. | authorlink12 = Marjorie van de Sande
| title = Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Clinical Working Case Definition, Diagnostic and Treatment Protocols
| journal = Journal of Chronic Fatigue Syndrome | volume = 11 | issue = 2 | page = 7-115
| date = 2003
| pmid =
| doi = 10.1300/J092v11n01_02
| url = http://www.investinme.org/Documents/PDFdocuments/CanadianDefinitionME-CFS.pdf
}}</ref><ref name="ICC2011primer">{{citation
| last1 = Carruthers | first1 = BM | authorlink1 = Bruce Carruthers
| last2 = van de Sande | first2 = MI | authorlink2 = Marjorie van de Sande
| last3 = De Meirleir | first3 = KL | authorlink3 = Kenny de Meirleir
| last4 = Klimas | first4 = NG | authorlink4 = Nancy Klimas
| last5 = Broderick | first5 = G | authorlink5 = Gordon Broderick
| last6 = Mitchell | first6 = T | authorlink6 = Terry Mitchell
| last7 = Staines | first7 = D | authorlink7 = Donald Staines
| last8 = Powles | first8 = ACP | authorlink8 = A C Peter Powles
| last9 = Speight | first9 = N | authorlink9 = Nigel Speight
| last10 = Vallings | first10= R | authorlink10= Rosamund Vallings
| last11 = Bateman | first11= L | authorlink11= Lucinda Bateman
| last12 = Bell | first12= DS | authorlink12= David Bell
| last13 = Carlo-Stella | first13= N | authorlink13= Nicoletta Carlo-Stella
| last14 = Chia | first14= J | authorlink14= John Chia
| last15 = Darragh | first15= A | authorlink15= Austin Darragh
| last16 = Gerken | first16= A | authorlink16= Anne Gerken
| last17 = Jo | first17= D | authorlink17= Daehyun Jo
| last18 = Lewis | first18= DP | authorlink18= Donald Lewis
| last19 = Light | first19= AR | authorlink19= Alan Light
| last20 = Light | first20= KC | authorlink20= Kathleen Light
| last21 = Marshall-Gradisnik | first21= S | authorlink21= Sonya Marshall-Gradisnik
| last22 = McLaren-Howard | first22= J | authorlink22= John McLaren-Howard
| last23 = Mena | first23= I | authorlink23= Ismael Mena
| last24 = Miwa | first24= K | authorlink24= Kunihisa Miwa
| last25 = Murovska | first25= M | authorlink25= Modra Murovska
| last26 = Stevens | first26= SR | authorlink26= Staci Stevens
| title = Myalgic encephalomyelitis: Adult & Paediatric: International Consensus Primer for Medical Practitioners
| date = 2012
| isbn = 978-0-9739335-3-6
| url = http://www.investinme.org/Documents/Guidelines/Myalgic%20Encephalomyelitis%20International%20Consensus%20Primer%20-2012-11-26.pdf
}}</ref>
# The [[Canadian Consensus Criteria]] (2003) for diagnosing ME/CFS lists "new sensitivities to food, medications and/or chemicals" as a symptom and MCS as a comorbidity;
# The [[International Consensus Criteria]] (2011) for diagnosing ME lists "sensitivities to food, medications, odors or chemicals" as a symptom and MCS as a comorbidity; and
# A 2019 publication of the U.S. ME/CFS Clinician Coalition lists "chemical sensitivity" as a symptom of ME/CFS and MCS as a comorbidity.<ref>{{Cite web|last=U.S. ME/CFS Clinician Coalition|date =Aug 2019|url =https://drive.google.com/file/d/1SG7hlJTCSDrDHqvioPMq-cX-rgRKXjfk/view|title = “Diagnosing and Treating ME/CFS”}}.</ref>
ME/CFS patients who also have MCS are more likely to face difficulties and complexities associated with accessing healthcare, supportive services and accommodation than those who don't. As well, if they have problems tolerating medications, this could complicate the management of their ME/CFS symptoms.
==How do you treat multiple chemical sensitivity? ==
[[File:Stock adobe oxygen.jpg|thumb|Is there a cure for multiple chemical sensitivity? At this time, there is no clinically proven cure. There is agreement that people with MCS need to avoid triggers to reduce symptoms and the likelihood of the condition worsening over time, which typically happens without avoidance.<ref name="Rossi2018" /> Medical Oxygen has been shown to reduce the severity of reactions and temporarily improve tolerance in some people.<ref name="Ch4.2" /><ref name="Ch4.5" />]]
There is no clinically proven cure for MCS.<ref name=":7" /><ref name=":10">{{Cite book |trans-chapter=4.1 "First, do no harm": environmental chemical avoidance|chapter=4.1 "Innanzitutto, non nuocere": l'evitamento chimica ambientale|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|quote='Numerous legislative initiatives in the United States, Canada, Australia, Japan and Germany protect the right of MCS patients to work, education, safe housing and social participation through different protocols of environmental chemical avoidance...' [Translated from Italian]}}</ref> There is also no scientific consensus on supportive therapies, "but the literature agrees on the need for patients with MCS to avoid the specific substances that trigger reactions for them and also on the avoidance of xenobiotics in general, to prevent further sensitization."<ref name=":6" /><ref name=":7" /><ref name="Valderrama2015" /><ref name=":49" /><ref name=":10" />

A study, which surveyed more than 900 people with MCS about their experiences managing the condition, found that 95% of respondents thought that "creating a chemical-free living space and chemical avoidance" had been the best strategy out of any management or treatment option they had tried.<ref name=":6" /><ref>{{cite journal|last=Gibson|first=PR|last2=Elms|first2=AN|last3 =Ruding|first3=LA|date=2003|title =Perceived treatment efficacy for conventional and alternative therapies reported by persons with multiple chemical sensitivity|journal =Environ Health Perspect|volume=111|pages =1498-1504|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.5936}}</ref>

There is also consensus that a multidisciplinary approach is required for adequately managing the health of someone with MCS.<ref name="pmid30088144" /><ref name=":10" /> Some studies suggest a special focus on correcting any nutritional deficiencies may be beneficial.<ref name="pmid30088144" /><ref name=":10" /><ref name=":35">{{Citation|last =Victoria Department of Health|date =2011|title =Multiple Chemical Sensitivities: A guide for Victorian hospitals|url=https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals}}</ref>

There is evidence that some patients with MCS have poor tissue oxygenation when exposed to triggers,<ref name="Ch4.5">{{Cite book|chapter=4.5 Terapia con ossigeno e camera iperbarica|trans-chapter=4.5 Oxygen therapy and hyperbaric oxygen|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> likely because of oxidative stress or because neural inflammation has reduced blood flow.<ref name="Ch4.5" /><ref name="Horvath1998">{{Cite journal|last=Horvath|first=I.|last2=Loukides|first2=S.|last3=Wodehouse|first3=T.|last4=Kharitonov|first4=S. A.|last5=Cole|first5=P. J.|last6=Barnes|first6=P. J.|date=1998-10-01|title=Increased levels of exhaled carbon monoxide in bronchiectasis: a new marker of oxidative stress|url=https://thorax.bmj.com/content/53/10/867|journal=Thorax|language=en|volume=53|issue=10|pages=867–870|doi=10.1136/thx.53.10.867|issn=0040-6376|pmid=10193374}}</ref><ref>{{Cite journal|last=Ewing|first=James F.|last2=Maines|first2=Mahin D.|date=1993|title=Glutathione Depletion Induces Heme Oxygenase-1 (HSP32) mRNA and Protein in Rat Brain|url=https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1471-4159.1993.tb03315.x|journal=Journal of Neurochemistry|language=en|volume=60|issue=4|pages=1512–1519|doi=10.1111/j.1471-4159.1993.tb03315.x|issn=1471-4159}}</ref><ref>{{Cite journal|last=Gregersen|first=Per|last2=Klausen|first2=Hans|last3=Elsnab|first3=Charlotte Uldal|date=1987|title=Chronic toxic encephalopathy in solvent-exposed painters in Denmark 1976–1980: Clinical cases and social consequences after a 5-year follow-up|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/ajim.4700110403|journal=American Journal of Industrial Medicine|language=en|volume=11|issue=4|pages=399–417|doi=10.1002/ajim.4700110403|issn=1097-0274}}</ref> Breathing medical oxygen following accidental chemical exposures is a suggested remedy for these patients.<ref name="Ch4.5" /> The 2019 consensus and clinical guidelines on MCS said that people with MCS "must be guaranteed, according to their individual needs and level of disability" medical oxygen and the necessary equipment to use it (that is, tubing and a mask from non-triggering materials).<ref name="Ch4.2">{{Cite book|trans-chapter=4.2 Therapeutic aids for subjects with disabilities for MCS|chapter=4.2 Ausili terapeutici per soggetti con invalidità per MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

The other aids the 2019 consensus said were necessary for patients with MCS to manage the functional impacts of their condition were: face masks (with HEPA and VOC filters), portable air purifiers for the home and for inside vehicles (made of metal, with HEPA and activated carbon filters) and water purifiers.<ref name="Ch4.2" />

In Australia in 2021 there will be an observational trial of MCS patients using [[Nimodipine|Nimodipine,]] a calcium-channel blocker which has been used to treat light and sound sensitivities in people with certain types of brain hemorrhage.

== Multiple chemical sensitivity and access ==
“A growing number of people report being affected by sensitivity to chemicals used in the building, maintenance and operation of premises," according to the Australian Human Rights and Equal Opportunity Commission. "This can mean that premises are effectively inaccessible to people with chemical sensitivity.”<ref name="Aus-HR">Australian Human Rights and Equal Opportunity Commission (2007), [http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem ''Australian Human Rights Commission Access: Guidelines and information''], Canberra</ref>

Various organisations and workplaces have policies which cite chemical or fragrance sensitivities as a disability access or occupational health and safety issue.<ref name=":7" /><ref name="Grenvillebook" /><ref>{{Cite book|title=The case against fragrance|pages=|isbn=9781925355956|edition=1st|volume=|language=|title-link=|url=|access-date=|date=2017|publisher=The text publishing company|last=Grenville|first=Kate|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Melbourne Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref>Blundell, Sally. [https://www.noted.co.nz/health/health-health/the-case-against-fragrance-the-potential-harm-of-our-perfumed-world The case against fragrance: The potential harm of our perfumed world.] Accessed Mar 22, 2017. Accessed 14 Feb 2020. ''"Canada has a range of fragrance-free hospitals, workplaces and concert venues. Vancouver International Airport has a fragrance-free route through its duty-free shops. Australia’s occupational health and safety regulator Workplace OHS says on its website that it is in the employers’ best interests “to address the issue of perfumes and personal sprays in the workplace” as perfumes and other scents can “adversely affect workers’ health, causing headaches, nausea, dizziness, upper respiratory symptoms, skin irritation and difficulty with concentration”."''</ref><ref name="ehs">{{Cite web|url=https://ehs.utoronto.ca/our-services/occupational-hygiene-safety/guidelines-on-the-use-of-perfumes-and-scented-products/|title=Guidelines on the Use of Perfumes and Scented Products|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=University of Toronto|archive-url=|archive-date=|access-date=2020-06-10}}</ref><ref name="Bennett2020" /><ref name="Flegel2015">{{Cite journal|last=Flegel|first=Ken|last2=Martin|first2=James G.|date=2015-11-03|title=Artificial scents have no place in our hospitals|url=http://www.cmaj.ca/lookup/doi/10.1503/cmaj.151097|journal=Canadian Medical Association Journal|language=en|volume=187|issue=16|pages=1187–1187|doi=10.1503/cmaj.151097|issn=0820-3946|pmc=4627866|pmid=26438018}}</ref><ref name=":28" /><ref name=":51" /><ref name=":54" /><ref name="princeed" /><ref name=":8" /><ref name=":19" /><ref name=":25" /><ref name=":27" /><ref name=":32" /><ref name=":33" /> The most influential of these may be the indoor air quality policy of the the U.S. [[Centers for Disease Control and Prevention]] (CDC), which says:
# "Scented or fragranced products are prohibited at all times in all interior space owned, rented, or leased by CDC;"<ref name="IEQP" />
# "CDC encourages employees to be as fragrance-free as possible when they arrive in the workplace...Employees should avoid using scented detergents and fabric softeners on clothes worn to the office. Many fragrance-free personal care and laundry products are easily available and provide safer alternatives;" and
# "Fragrance is not appropriate for a professional work environment, and the use of some products with fragrance may be detrimental to the health of workers with chemical sensitivities, allergies, asthma, and chronic headaches/migraines."<ref name="IEQP" />
Common ingredients in synthetic fragrance are recognized as irritants for a range of respiratory conditions.<ref>"Section 1: Allergic Sensitivity to Fragrances: A Growing Health Concern" [https://www.ewg.org/sites/default/files/report/SafeCosmetics_FragranceRpt.pdf Not so sexy. The health risks of secret ingredients in fragrance] The campaign for safe cosmetics. The Environmental Working Group. 2010. </ref><ref>{{Cite journal|last=Steinemann|first=Anne|last2=Goodman|first2=Nigel|date=2019-06-01|title=Fragranced consumer products and effects on asthmatics: an international population-based study|url=https://doi.org/10.1007/s11869-019-00693-w|journal=Air Quality, Atmosphere & Health|language=en|volume=12|issue=6|pages=643–649|doi=10.1007/s11869-019-00693-w|issn=1873-9326}}</ref><ref>Nazaroff, W.W. Welsher, C.J. Cleaning products and air fresheners: exposure to primary and secondary air pollutants. ''Atmos. Environ''., 38 (2004), pp. 2841-2865</ref><ref>Kumar, P.; Caradonna, V.M; Graham, S. Gupta, X. Cai, P.N. Rao, J. Thompson ''Inhalation challenge effects of perfume scent strips in patients with asthma,'' Ann. Allergy Asthma Immunol., 75 (5) (1995), pp. 429-433</ref><ref>Elberling J, Linneberg A, Mosbech H, Dirksen A, Frølund L, Madsen F, Nielsen NH, Johansen JD. 2004. A link between skin and airways regarding sensitivity to fragrance products? Br J Dermatol. 151(6): 1197-203. </ref><ref>Elberling J, Lerbaek A, Kyvik KO, Hjelmborg J. A twin study of perfume related respiratory symptoms. ''Int J Hyg Environ Health.'' 2009; 212(6): 670-8.</ref><ref>Mendell. M.J. Indoor residential chemical emissions as risk factors for respiratory and allergic effects in children: a review. ''Indoor Air.'' 2007; 17(4):259-77.</ref><ref>Schnuch A, Oppel E, Oppel T, Römmelt H, Kramer M, Riu E, Darsow U, Przybilla B, Nowak D, Jörres RA. 2010. Experimental inhalation of fragrance allergens in predisposed subjects: effects on skin and airways. ''Br J Dermatol''.</ref><ref>Neuenschwander U, Guignard F, Hermans I. 2010. Mechanism of the aerobic oxidation of alpha-pinene. ''ChemSusChem''. 3(1): 75-84.</ref><ref>Nielsen GD, Larsen ST, Hougaard KS, Hammer M, Wolkoff P, Clausen PA, Wilkins CK, Alarie Y. 2005. Mechanisms of acute inhalation effects of (+) and (-)-alpha-pinene in BALB/c mice. ''Basic Clin Pharmacol Toxicol.'' 96(6):420-8.</ref><ref>Rohr AC, Wilkins CK, Clausen PA, Hammer M, Nielsen GD, Wolkoff P, Spengler JD. 2002. Upper airway and pulmonary effects of oxidation products of (+)-alpha-pinene, d-limonene, and isoprene in BALB/c mice. ''Inhal Toxicol''. 14(7): 663-84.</ref><ref>Venkatachari P, Hopke PK. 2008. Characterization of products formed in the reaction of ozone with alpha-pinene: case for organic peroxides. ''J Environ Monit.'' 10(8): 966-74.</ref> The American Lung Association lists fragrance on their list of "indoor air pollutants" and recommends that healthy workplaces establish fragrance-free policies for employees and visitors."<ref name="Grenvillebook" />{{Rp|30}} With this in mind, some have called for fragrance-free policies in hospitals and healthcare settings.

There is ancedotal evidence of people with MCS facing significantly higher levels of disability as a direct result of certain Covid-19 policies. This is said to be "due to greater exposure to disinfectants and fragranced products as well as increased barriers to essential needs such as food and healthcare."<ref>The Environmental Health Association of Quebec (2020). [https://aseq-ehaq.ca/en/projects/mcs-covid-19/ Impacts of Covid-19 Health measures on people with multiple chemical sensitivities].</ref>
=== Hospital care ===
Hospitals with fragrance-free policies are common Canada and Sweden.<ref name="Bennett2020">Bennett, Holly (Jul 2 2020). [https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds Common chemical products making Australians sick, study finds]. Melbourne University Press blog. Melbourne, Australia. Accessed 14 Feb 2020. ''"Professor Steinemann recommends choosing products without any fragrance, and implementing fragrance-free policies in workplaces, health care facilities, schools and other indoor environments."''</ref><ref name="Grenvillebook" /><ref name=":7" /><ref name="Flegel2015" /><ref name=":28">[https://www.mountsinai.on.ca/about_us/policies/scented-products-and-fragrances-policy Scented products and fragrances policy] Mount Sinai Hospital, Ontario, Canada. </ref><ref name=":51">[https://kingstonhsc.ca/patients-families-and-visitors/visiting-patient/smoke-free-scent-free-latex-free Smoke Free, Scent Sensitive, Latex Sensitive]. Kinston Health Sciences Centre. Canada. 2020. </ref><ref name=":54">[https://www.ottawahospital.on.ca/en/patients-visitors/visiting-the-hospital/ Visiting the hospital]. The Ottawa Hospital. Ottawa, Canada.</ref><ref name="princeed">[https://www.princeedwardisland.ca/sites/default/files/publications/souris_hospital_patient_and_family_booklet.pdf Souris Hospital Patient and Family Information Booklet 2017-2018] Prince Edward Island, Canada. </ref><ref name=":8">[https://www.stjoes.ca/patients-visitors/your-visit-or-stay/scent-free-campuses/007-ohs.pdf St Joseph's healthcare scent free policy] St Joseph's healthcare, Hamilton, Canada. </ref><ref name=":19">[https://www.msh.on.ca/sites/default/files/Human%20Resources/Policies/1_045_Fragrance_Reduced_Workplace__000010001.pdf Scent free policy (2007).] Markham Stouffville Hospital. Canada. </ref><ref name=":25">[https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Scent-free policy]. [https://www.mackenziehealth.ca/en/patients-visitors/safety.aspx Mackenzie Health hospitals.] MAD, Ontario, Canada</ref><ref name=":27">[https://www.camh.ca/en/your-care/visiting-camh Visiting CAMH] Ontario, Canada. </ref><ref name=":32">[https://www.fraserhealth.ca/Service-Directory/Locations/Mission/mission-memorial-hospital#.XrLKnKgzbIU Mission Memorial Hospital] British Columbia, Canada</ref><ref name=":33">[https://www.southwesthealthline.ca/pdfs/sbghc_patientandfamilyguide2019_chesley.pdf Patient and Family Guide] South Bruce Grey Health Center, Ontario, Canada. </ref> Canadian examples include:
* Mount Sinai Hospital has a fragrance-free policy, which says the hospital "is committed to providing a safe and inclusive environment for all and will strive to eliminate the use of products with scents and fragrances to prevent any adverse reactions in patients, staff and other people working and/or visiting the hospital premises."<ref name=":28" />
* Kingston General Hospital is fragrance free "for the safety and comfort of those with allergies and sensitivities," and its web site says "other items that you should not use or bring when you visit the hospital include: perfumes and colognes, scented fabric softeners, stain removers and laundry detergents, scented soaps and deodorant, scented shampoos and hair products, scented body powders and lotions."<ref name=":51" />
As well as fragrance-free policies, to prevent adverse reactions and improve health outcomes in hospital settings, patients with MCS often require adjustments in chemical use, medications and anesthetics.<ref>[https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf]{{citation|chapter=5. Osdepali per MCS|trans-chapter=5. Hospitals and MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf|title=[The Italian Consensus] Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=[Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS]|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23|first=|last2=|first2=|author-link=|volume=|issue=|pages=|edition=|isbn=}}</ref><ref name=":36">{{Cite web|url=http://www.lassentech.com/eimcspro.html|title=Mercy Medical Center Process Standards, Multiple Chemical Sensitivity Protocol|date =1999}}</ref><ref>Fisher MM, Rose M. [https://pubmed.ncbi.nlm.nih.gov/18782886/ Anaesthesia for patients with idiopathic environmental intolerance and chronic fatigue syndrome]. Br J Anaesth 2008; 101(4): 486-91.</ref><ref>Rea, William J. 1996 "41 Surgery in the chemically sensitive," ''Chemical Sensitivity Tools of Diagnosis and Methods of Treatment'', Environmental Health Center, Dallas, Texas. CRC Press. </ref><ref name=":53">{{citation |url =https://www2.health.vic.gov.au/about/publications/policiesandguidelines/Multiple-Chemical-Sensitivity-A-guide-for-Victorian-hospitals|title = Multiple Chemical Sensitivity -- A guide for Victoria hospitals|date =Aug 25, 2011|website =Victoria Health}}</ref><ref name=":38">{{Cite web|url =http://www.health.act.gov.au/sites/default/files/2018-09/Multiple%20Chemical%20Sensitivities%20Procedure.docx|title=Canberra Hospital and Health Services Clinical Procedure: Multiple Chemical Sensitivities|date =2018|last=ACT Department of Health|access-date=|website=|first=Canberra, Australia|authorlink=|last2=|first2=|authorlink2=|archive-url=|archive-date=}}</ref><ref name=":34">{{Cite web|url=https://www.health.nsw.gov.au/factsheets/Pages/multiple-chemical-sensitivity.aspx|title=Fact sheet: Multiple Chemical Sensitivity Disorder|last=NSW Health|first=|authorlink=|last2=|first2=|authorlink2=|date=2019|website=www.health.nsw.gov.au|archive-url=|archive-date=|access-date=2020-05-14}} </ref><ref name=":37">{{Cite web|last=Australian Commission on Safety and Quality in Health Care|date=2017|url=http://www.cec.health.nsw.gov.au/__data/assets/pdf_file/0006/258081/National-Safety-and-Quality-Health-Service-Standards-Guide-for-Hospitals.pdf|title=National Safety and Quality Health Service Standards Guide for Hospitals|publisher=NSW health |location=Canberra, Australia}}</ref><ref name=":52">{{Cite web|url =https://www.sahealth.sa.gov.au/wps/wcm/connect/b9c3d3004f51c10eae91eedd8959a390/Guideline_IEI-MCS+Guidelines+for+Hospitals_13122016.pdf|title =Idiopathic Environmental Intolerance or Multiple Chemical Sensitivity Policy Guideline|date =Aug 26, 2016|website =South Australia Health|location =Adelaide, Australia}}</ref><ref name=":39">[http://www.parliament.wa.gov.au/publications/tabledpapers.nsf/displaypaper/3814445c4f180533eea73781482579f2000ec798/$file/4445.pdf Multiple Chemical Sensitivity Chemical Hypersensitivity Guideline. Sep 14, 2010.] Western Australia Country Health Service. Western Australia.</ref>

Some states and regions have specific policies for the hospital care of patients with MCS. For example, in Australia, three states and a territory have detailed hospital policies for patients with MCS.<ref name=":38" /><ref name=":53" /><ref name=":39" /><ref name=":52" /> As well, some individual hospitals have their own policies for MCS patients.<ref>[http://www.lassentech.com/eimcspro.html Multiple Chemical Sensitivity Protocol.] Mercy Medical Centers New York and California.09/1999.</ref><ref>[https://www.qhc.on.ca/multiple-chemical-sensitivities--p279.php Multiple Chemical Sensitivities]. Jan 2010. QHC Healthcare, Ontario, Canada. </ref>

=== '''Accommodation''' ===
Chemically sensitive people typically encounter difficulties finding suitable housing and homelessness is a common problem for people with this condition.<ref>{{Cite book|title=Amputated Lives: Coping with Chemical Sensitivity|pages=16-26|isbn=|edition=1st edition|volume=|language=|title-link=|url=|access-date=|date=November 20, 2008|publisher=Cumberland Press|last=Johnson|first=Alison|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=Parramatta, Australia|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref> A 2002 housing survey of people with chemical sensitivities found that:
* 57% of respondents had experienced homelessness during their illness (compared to 1% of the general population reporting having experienced homeless in their lifetime)
* 25% had lived in a car (nine months average)
* 15% had lived in a tent (eight months average)
* 73% of respondents had lived in a house that made them sick
* 47% said they were spending more than they could afford on accessible housing
* 43% said their current housing was neither accessible nor permanent.<ref>{{Cite journal|last=Environmental Health Coalition|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=March 11, 2002|title=Homelessness at critical level for Western Massachusetts chemically injured|url=www.gov.mass|journal=|location=Western Massachusetts|volume=|issue=|pages=|doi=|pmc=|pmid=|access-date=|quote=|via=}}</ref>

==How common is multiple chemical sensitivity? ==
[[File:High sensitivity image.jpg|thumb|Multiple chemical sensitivity is not a rare disease. Some studies show it is increasing in prevalence.<ref name="Steinemann2018" /> ]]While prevalence rates for MCS vary according to the diagnostic criteria used,<ref name="Ch2" /><ref name="Ch1-1-2">{{Cite book|chapter=1.1.2 Studies on the prevalence of MCS in other countries|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref> the condition is reported across industrialized countries and the data suggests it affects women more than men.<ref name="Rossi2018" /><ref name=":7" />{{Rp|37}}<ref name="Carress2004">{{Cite journal|vauthors=Caress SM, Steinemann AC|date=May 2004|title=Prevalence of Multiple Chemical Sensitivities: A Population-Based Study in the Southeastern United States|journal=Am J Public Health|volume=94|issue=5|pages=746–747|pmc=1448331|pmid=15117694|doi=10.2105/ajph.94.5.746|url=https://ajph.aphapublications.org/doi/pdfplus/10.2105/AJPH.94.5.746}}</ref><ref name="Berg2008">{{Cite journal|last=Berg|first=Nikolaj Drimer|last2=Linneberg|first2=Allan|last3=Dirksen|first3=Asger|last4=Elberling|first4=Jesper|date=2008-07-01|title=Prevalence of self-reported symptoms and consequences related to inhalation of airborne chemicals in a Danish general population|url=https://doi.org/10.1007/s00420-007-0282-0|journal=International Archives of Occupational and Environmental Health|language=en|volume=81|issue=7|pages=881–887|doi=10.1007/s00420-007-0282-0|issn=1432-1246}}</ref><ref>{{Cite journal|last=Andersson|first=Linus|last2=Johansson|first2=Åke|last3=Millqvist|first3=Eva|last4=Nordin|first4=Steven|last5=Bende|first5=Mats|date=2008-10-01|title=Prevalence and risk factors for chemical sensitivity and sensory hyperreactivity in teenagers|url=http://www.sciencedirect.com/science/article/pii/S1438463908000199|journal=International Journal of Hygiene and Environmental Health|language=en|volume=211|issue=5|pages=690–697|doi=10.1016/j.ijheh.2008.02.002|issn=1438-4639}}</ref><ref>{{Cite journal|last=Bloch|first=Richard M.|last2=Meggs|first2=William J.|date=2007-01-01|title=Comorbidity patterns of self‐reported chemical sensitivity, allergy, and other medical illnesses with anxiety and depression|url=https://doi.org/10.1080/13590840701352823|journal=Journal of Nutritional & Environmental Medicine|volume=16|issue=2|pages=136–148|doi=10.1080/13590840701352823|issn=1359-0847}}</ref><ref>{{Cite journal|vauthors=Gibson PR, Lockaby SD, Bryant JM|date=Apr 6, 2016|title=Experiences of persons with multiple chemical sensitivity with mental health providers|url=https://pdfs.semanticscholar.org/7659/1bc4c83ad211c5cd3b4a5b1f67c74f731048.pdf|journal=Journal of Multidisciplinary Healthcare|volume=9|pages=163–172|via=}}</ref><ref name="Valderrama2015" />{{Rp|2,39}}

The most extensive epidemiological study into MCS in the U.S. was in 2005.<ref name="Ch2" /><ref name="Steinemann2005">{{Cite journal|url=https://www.tandfonline.com/doi/abs/10.3200/AEOH.58.6.300-305|last=Steinemann AC.|title=A national population study of the prevalence of multiple chemical sensitivity|journal=Arch Environ Health |date=2005|volume=59|issue=6)|pages=300-5}}</ref> It found that the national prevalence rate for MCS diagnosed by a doctor was 2.5% and self-reported MCS was 11.2%.<ref name="Ch2" /><ref name="Steinemann2005" /><ref name="Caress2009">{{Cite journal|last=Caress|first=SM|last2=Steinemann|first2=AC|date=2009-02-01|title=Asthma and chemical hypersensitivity: prevalence, etiology, and age of onset|url=https://doi.org/10.1177/0748233709102713|journal=Toxicology and Industrial Health|language=en|volume=25|issue=1|pages=71–78|doi=10.1177/0748233709102713|issn=0748-2337}}</ref>

In 2018, the same researchers reported that the prevalence rate of diagnosed MCS had increased by more than 300% and self-reported chemical sensitivity by more than 200% in the previous decade.<ref name="Ch2" /><ref name="Steinemann2018" /> They found that 12.8% of those surveyed reported medically diagnosed MCS and 25.9% reported having chemical sensitivities.<ref name="Ch2" /><ref name="Steinemann2018" />

A 2014 study by the Canadian Ministry of Health estimated, based on its survey, that 0.9% of Canadian males and 3.3% of Canadian females had a diagnosis of MCS by a health professional.<ref name=":7" />{{Rp|37}}<ref>Canadian Community Health Survey (CCHS) 2014, Ministry of Health and Long-Term Care Share File, Statistics Canada.</ref>

In Denmark, the Ministry of the Environment estimated in 2004 that 10% of the population was sensitive to certain everyday chemicals and that 1% of the population had MCS to a level that was disabling.<ref name="infoamuca2014">{{Cite web|url=https://www.infoamica.it/danimarca-nuovo-codice-per-la-mcs/|title=Danimarca: nuovo codice per la MCS|last=|first=|authorlink=|last2=|first2=|authorlink2=|date=2014|website=|language=it-IT|trans-title=Denmark: A new code for MCS|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

While a 2018 study at the University of Melbourne found that 6.5% of Australian adults reported having a medical diagnosis of MCS and that 18.9% reported having adverse reactions to multiple chemicals.<ref name="Ch2" /><ref name=":50">{{Cite journal|last=Pigatto|first=Paolo D.|last2=Guzzi|first2=Gianpaolo|date=2019-06-01|title=Prevalence and risk factors for multiple chemical sensitivity in Australia|url=http://www.sciencedirect.com/science/article/pii/S2211335519300415|journal=Preventive Medicine Reports|language=en|volume=14|pages=100856|doi=10.1016/j.pmedr.2019.100856|issn=2211-3355}}</ref><ref name=":21">{{Cite news|url=https://about.unimelb.edu.au/newsroom/news/2018/july/common-chemical-products-making-australians-sick-study-finds|title=Common chemical products making Australians sick, study finds|last=|first=|date=Jul 2, 2018|work=The University of Melbourne Newsroom|access-date=Nov 20, 2019}}</ref><ref>[https://www.sciencedirect.com/science/article/pii/S2211335518300457 Steinemann A. Prevalence and effects of multiple chemical sensitivities in Australia. ''Prev Med Rep'' 2018; 10: 191-4.</ref> The study also found that for 55.4% of those with MCS, the symptoms triggered by chemical exposures could be disabling.<ref name=":21" /><ref name="Steinemann2018" />

These findings show that in the above countries MCS is not a rare disease.

==What causes multiple chemical sensitivity? ==
In 2017, a Canadian government Task Force on Environmental Health said that there had been very little rigorous peer-reviewed research into MCS and almost a complete lack of funding for such research in North America.<ref name=":7" />{{Rp|53}} "Most recently," it said, "some peer-reviewed clinical research has emerged from centres in Italy, Denmark and Japan suggesting that there are fundamental neurobiologic, metabolic, and genetic susceptibility factors that underlie ES (Environmental Sensitivities)/MCS."<ref name=":7" />{{Rp|53}}

The Italian consensus on MCS of 2019 said that the current consensus what is the cause of MCS is that it likely has multiple causes—chiefly biochemical and neuro-physiological and also causes related to the limbic system and perhaps also genetic predisposition.<ref name=":4">{{citation|trans-chapter=1.4 Proposed mechanisms for MCS|chapter=1.4 Meccanismo proposti per la MCS|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

When speaking at an Australian federal parliamentary inquiry into environmental illness, in 2018, Dr Graeme Edwards, the inquiry's representative of Royal Australasian College of Physicians<ref name=":40">''[https://www.racp.edu.au/docs/default-source/advocacy-library/racp-submission-to-the-australian-parliament-s-health-aged-care-and-sport-committee-inquiry-into-biotoxin-related-illnesses-in-australia.pdf?sfvrsn=7ae3131a_4 Royal Australasian College of Physicians' Submission to the Australian Parliament’s Health, Aged Care and Sport Committee Inquiry into Biotoxin-related Illnesses in Australia]'', Aug 2018. ''“Dr Graeme Edwards represented the RACP at this public hearing and we trust the Committee benefited from his contribution to the discussions.”'' p.1.</ref> said that there was "relatively good consensus" that causation was multifactorial. "There is no single causative factor," he said. "It is a combination of factors ... unless you have all the pieces of the puzzle lining up, you actually don't get the disease. And because we are talking about multi-dimensional triggers, any one individual, at any one point in time, may not have exposure to all of those triggers to get a pathological result. And therein lies the complexity."<ref name="Hansard9Aug2018" />{{Rp|11}}

These recent statements suggest that earlier depictions of MCS as being ''either'' biologically or psychologically caused likely set up a false dichotomy or dilemma.

=== Toxicological ===
It has been hypothesized that MCS is caused by exposure to particular chemicals—most commonly certain pesticides.

Professor [[Martin Pall|Martin L. Pall]] proposed that MCS had a toxicological and biochemical cause, and that "seven individual chemicals or chemical classes—organophosphorus/carbamate, organochloride and pyrethroid pesticides, organic solvents, carbon monoxide, hydrogen sulphide and mercury/mercurial compounds—could initiate MCS through their ability to increase N-methyl-D-aspartate (NMDA) receptor activity."<ref name=":9" /><ref name="MCSsymp" /> [[File:Herbicide spraying generic.jpg|thumb|Is multiple chemical sensitivity caused by pesticides? Some MCS researchers think it often is. The most recent consensus paper on MCS (2019) said this hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses.<ref name=":4" />]]
Pall hypothesized that overactivity of the NMDA receptors, coupled with stress-related increases in [[nitric oxide]] and the oxidative product [[peroxynitrite]] (known as the [[Nitric oxide hypothesis|NO/ONOO cycle]]) caused MCS symptoms and worsened the condition.<ref name=":15">{{Cite book|title=[[Explaining "Unexplained Illnesses"|Explaining "Unexplained illnesses": Disease Paradigm for Chronic Fatigue Syndrome, Multiple Chemical Sensitivity, Fibromyalgia, Post-Traumatic Stress Disorder, Gulf War Syndrome and Others]]|last=Pall|first=Martin L.|publisher=Routledge & Harrington Park Press|year=2007|isbn=978-0789023896|location=New York}}</ref><ref>{{Cite journal|vauthors=Pall ML, Satterlee JD|date=2001|title=Elevated nitric oxide/peroxynitrite mechanism for the common etiology of multiple chemical sensitivity, chronic fatigue syndrome, and Post Traumatic stress disorder|url=https://semanticscholar.org/paper/d804ba7af6079f3d70cf1f4feb43d17d4e22a021|journal=Annals of the New York Academy of Sciences|volume=933|issue=1|pages=323–9|via=|doi=10.1111/j.1749-6632.2001.tb05836.x|pmid=12000033|bibcode=2001NYASA.933..323P}}</ref> He suggested that hypersensitivity occurred because of limbic kindling, neural sensitization, and/or neurogenic inflammation—processes which could be driven by the NO/ONOO cycle.<ref name="MCSsymp">{{Cite book|chapter=What are the symptoms of MCS|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx}}</ref>

A 2019 scientific review said that while further research was required to confirm Pall's theory, that his hypothesis "had found broad consensus in the scientific community” and was compatible with previous hypotheses,<ref name=":4" /> including Dr. Iris Bell's theory of neuronal sensitization<ref name=":17">{{Cite journal|last=Bell|first=Iris R.|last2=Baldwin|first2=Carol M.|last3=Fernandez|first3=Mercedes|last4=Schwartz|first4=Gary E.R.|date=1999-04-01|title=Neural sensitization model for multiple chemical sensitivity: overview of theory and empirical evidence|url=https://doi.org/10.1177/074823379901500303|journal=Toxicology and Industrial Health|language=en|volume=15|issue=3-4|pages=295–304|doi=10.1177/074823379901500303|issn=0748-2337}}</ref><ref name=":18">{{Cite journal|last=Bell|first=IR|author-link=|last2=Rossi|first2=J|author-link2=|last3=Gilbert|first3=ME|author-link3=|last4=Kobal|first4=G|author-link4=|last5=Morrow|first5=LA|author-link5=|last6=Newlin|first6=DB|author-link6=|last7=Sorg|first7=BA|last8=Wood|first8=RW|date=1997-03-01|title=Testing the neural sensitization and kindling hypothesis for illness from low levels of environmental chemicals.|url=https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2539|journal=Environmental Health Perspectives|volume=105|issue=suppl 2|pages=539–547|doi=10.1289/ehp.97105s2539|pmc=1469815|pmid=9167993|access-date=|quote=|via=}}</ref> and William Meggs’ theory of neurogenic inflammation.<ref name=":16">{{Cite journal|last=Meggs|first=William J.|date=2017-05-09|title=The Role of Neurogenic Inflammation in Chemical Sensitivity|url=https://www.liebertpub.com/doi/full/10.1089/eco.2016.0045|journal=Ecopsychology|volume=9|issue=2|pages=83–89|doi=10.1089/eco.2016.0045}}</ref>

It also said that Pall's theory may explain the comorbidity of MCS and other pathologies hypothesized to be related to the same mechanism, including [[fibromyalgia]] (FM) and [[ME/CFS]], and that it might be why MCS symptoms tend to lessen after exposure to inhibitors and/or antagonists of NMDA receptors.<ref name=":4" />The review also said that "pesticides, including herbicides, insecticides and agricultural chemicals, are among the substances most commonly implicated in the activation of MCS cases in the United States."<ref name="4.3">{{citation|chapter=4.3|trans-chapter=4.3 Reduction of risk|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref>

Pall's theory has also been used to explain why Gulf War veterans, particularly those who were exposed to [[organophosphate]] pesticides, have been found to be more likely to have MCS than the general population<ref>{{cite journal|vauthors=Reid S, et al|year=|title=Multiple Chemical Sensitivity and Chronic Fatigue Syndrome in British Gulf War Veterans|url=https://doi.org/10.1093%2Faje%2F153.6.604|journal=American Journal of Epidemiology|volume=153|issue=6|pages=604–9|doi=10.1093/aje/153.6.604|pmid=11257069|last=|first=|last2=|first2=|date=2001|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|access-date=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name=":15" /> as well as the fact that chemical sensitivities are a known symptom reported in [[Gulf War Illness|Gulf war syndrome]] or post-deployment syndrome.<ref>[https://europepmc.org/abstract/med/15757795 Gronseth GS. Gulf war syndrome: A toxic exposure? A systematic review. ''Neurol Clin''. May 2005;23(2):523-540.]</ref><ref name=":48" /><ref>{{Cite journal|last=Spelman|first=Juliette F.|last2=Hunt|first2=Stephen C.|last3=Seal|first3=Karen H.|last4=Burgo-Black|first4=A. Lucile|date=2012-09-01|title=Post Deployment Care for Returning Combat Veterans|url=https://doi.org/10.1007/s11606-012-2061-1|journal=Journal of General Internal Medicine|language=en|volume=27|issue=9|pages=1200–1209|doi=10.1007/s11606-012-2061-1|issn=1525-1497|pmc=3514997|pmid=22648608}}</ref>

The U.S. Department of Veterans Affairs concluded that "risk factors that may be associated with predisposing, precipitating, and perpetuating chronic multi system illnesses [including MCS] among veterans" included chemical exposure, and notably chemical exposure in the Gulf War, where some military personel were exposed to nerve agents (like sarin and cyclosarine) and toxic smoke.<ref name=":48">{{Cite web|url=https://www.healthquality.va.gov/guidelines/MR/cmi/VADoDCMICPG2014.pdf|title=Clinical practice guideline for the management of chronic multisystem illness|last=U.S. Department of Veterans Affairs, Department of Defense|date=Oct 2014}}</ref>

[[Mold]] and mycotoxin exposures have also been hypothesized to trigger the onset of MCS.<ref name="Rea2010">{{Cite journal|last=Rea|first=William J.|date=2018-06-01|title=A Large Case-series of Successful Treatment of Patients Exposed to Mold and Mycotoxin|url=http://www.sciencedirect.com/science/article/pii/S0149291818301899|journal=Clinical Therapeutics|language=en|volume=40|issue=6|pages=889–893|doi=10.1016/j.clinthera.2018.05.003|issn=0149-2918}}</ref><ref>{{Cite journal|last=Lieberman|first=Allan|last2=Rea|first2=William|last3=Curtis|first3=Luke|date=2006-09-01|title=Adverse health effects of indoor mold exposure|url=https://www.jacionline.org/article/S0091-6749(06)01396-0/abstract|journal=Journal of Allergy and Clinical Immunology|language=English|volume=118|issue=3|pages=763|doi=10.1016/j.jaci.2006.06.037|issn=0091-6749|pmid=16950304}}</ref><ref>{{Cite journal|last=Vojdani|first=Aristo|last2=Thrasher|first2=Jack D.|last3=Madison|first3=Roberta A.|last4=Gray|first4=Michael R.|last5=Heuser|first5=Gunnar|last6=Campbell|first6=Andrew W.|date=2003-07-01|title=Antibodies to Molds and Satratoxin in Individuals Exposed in Water-Damaged Buildings|url=https://doi.org/10.1080/00039896.2003.11879143|journal=Archives of Environmental Health: An International Journal|volume=58|issue=7|pages=421–432|doi=10.1080/00039896.2003.11879143|issn=0003-9896|pmid=15143855}}</ref><ref name="Hansard9Aug2018" /> Exposure to mold has already been associated with initiating inflammation and higher incidences of certain chronic conditions (like asthma), which are common symptoms of MCS.<ref>{{Cite book|last=Hänninen|first=Otto O.|author-link=|last2=|first2=|author-link2=|date=2011|editor-last=Adan|editor-first=Olaf C. G.|editor2-last=Samson|editor2-first=Robert A.|title=Fundamentals of mold growth in indoor environments and strategies for healthy living.|url=https://doi.org/10.3920/978-90-8686-722-6_10|journal=|chapter=World Health Organisation (WHO) Guidelines for Indoor Air Quality: dampness and mold.|language=en|location=Wageningen|publisher=Academic Publishers|pages=277–302|doi=10.3920/978-90-8686-722-6_10|isbn=978-90-8686-722-6|access-date=|quote=Toxicological evidence obtained in vivo and in vitro supports these findings, showing the occurrence of diverse inflammatory and toxic responses after exposure to microorganisms – including their spores, metabolites and components isolated from damp buildings. The increasing prevalence of asthma and allergies in many countries increase the number of people susceptible to the effects of dampness and mould in buildings.|via=|ISBN=}}</ref><ref name=":40" /><ref name="Knibbs2018">{{Cite journal|last=Knibbs|first=Luke D.|author-link=|last2=Woldeyohannes|first2=Solomon|author-link2=|last3=Marks|first3=Guy B.|author-link3=|last4=Cowie|first4=Christine T.|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2018|title=Damp housing, gas stoves, and the burden of childhood asthma in Australia|url=https://onlinelibrary.wiley.com/doi/abs/10.5694/mja17.00469|journal=Medical Journal of Australia|language=en|volume=208|issue=7|pages=299–302|doi=10.5694/mja17.00469|issn=1326-5377|pmc=|pmid=|access-date=|quote=Exposure to damp housing and gas stoves is common in Australia, and is associated with a considerable proportion of the childhood asthma burden.|via=}}</ref><ref>{{Cite journal|last=Quansah|first=Reginald|last2=Jaakkola|first2=Maritta S.|last3=Hugg|first3=Timo T.|last4=Heikkinen|first4=Sirpa A M.|last5=Jaakkola|first5=Jouni J. K.|date=2012-11-07|title=Residential Dampness and Molds and the Risk of Developing Asthma: A Systematic Review and Meta-Analysis|url=https://journals.plos.org/plosone/article/file?type=printable&id=10.1371/journal.pone.0047526|journal=PLoS ONE|volume=7|issue=11|pages=e47526|doi=10.1371/journal.pone.0047526|issn=1932-6203|pmc=3492391|pmid=23144822}}</ref><ref>{{Cite journal|last=Mendell|first=Mark J|author-link=|last2=Mirer|first2=Anna G|author-link2=|last3=Cheung|first3=Kerry|author-link3=|last4=Tong|first4=My|author-link4=|last5=Douwes|first5=Jeroen|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=2011-06-01|title=Respiratory and Allergic Health Effects of Dampness, Mold, and Dampness-Related Agents: A Review of the Epidemiologic Evidence|url=https://ehp.niehs.nih.gov/doi/full/10.1289/ehp.1002410|journal=Environmental Health Perspectives|volume=119|issue=6|pages=748–756|doi=10.1289/ehp.1002410|pmc=3114807|pmid=21269928|access-date=|quote=The authors reported evidence from epidemiologic studies and meta-analyses showed indoor dampness or mould to be associated consistently with increased asthma development and exacerbation, current and ever diagnosis of asthma, dyspnoea, wheeze, cough, respiratory infections, bronchitis, allergic rhinitis, eczema, and upper respiratory tract symptoms. Associations were found in allergic and non-allergic individuals. Evidence strongly suggested causation of asthma “exacerbation” in children.|via=}}</ref>
{{See also|Mold illness|Mold illness|Gulf War Illness|Gulf War Illness||}}

=== Neurological ===
Many common symptoms of MCS are neurological<ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="Ch1" /> (for example, "dizziness, seizures, [[headache|head pain]], fainting, loss of coordination"<ref name="Steinemann2018" />). And neurogenic inflammation and a [[central sensitization syndrome]] have been thought to be mechanisms involved in causing, perpetuating and worsening MCS.<ref name="Ch1" /><ref name=":17" /><ref name=":18" /><ref name=":16" /><ref>"Multiple chemical sensitivity: On the scent of central sensitization," ''International journal of hygiene and environmental health'' 216(2), April 2012. DOI: [https://www.researchgate.net/deref/http%3A%2F%2Fdx.doi.org%2F10.1016%2Fj.ijheh.2012.02.010 10.1016/j.ijheh.2012.02.010]
</ref>

William Meggs said that [[Neuroinflammation|neurogenic inflammation]] was a well-defined pathophysiological process, in which chemical irritants triggered nerve fibers to release inflammatory mediators, which led to disease. In a 2017 review, he said that with MCS, an initiating chemical exposure (commonly a respiratory irritant or pesticide) was usually identified in association with the onset of the disease.<ref name=":16" />

Iris Bell researched brain-wave patterns in people with MCS. He showed, in several studies using [[Electroencephalography]] (EEG), that people with MCS often had certain abnormal brain wave patterns.<ref name=":4" /><ref>[https://europepmc.org/abstract/med/7778120 Schwartz GE, Bell IR, Dikman ZV, et al. EEG responses to low-level chemicals in normals and cacosmics. ''Toxicol Ind Health'' 1994; 10(4-5): 633-43.]</ref> For example, he found that women with MCS were more likely to have greater resting alpha waves than controls, which he said suggested the possibility of central nervous system hypo-activation.<ref>[https://www.sciencedirect.com/science/article/pii/S000632239700245X Bell IR, Schwartz GE, Hardin EE, Baldwin CM, Kline JP. Differential resting quantitative electroencephalographic alpha patterns in women with environmental chemical intolerance, depressives, and normals. ''Biol Psychiatry'' 1998; 43(5): 376-88.]</ref>

Multiple neuro-imaging studies have shown that people with MCS often have other neurological abnormalities, including abnormal cerebral perfusion patterns, especially in the [[Autonomic nervous system|autonomic nervous system areas]].<ref name=":4" /><ref>[https://www.tandfonline.com/doi/abs/10.1080/15287399409531843 Callender TJ, Morrow L, Subramanian K. Evaluation of chronic neurological sequelae after acute pesticide exposure using SPECT brain scans. ''Toxicol Environ Health'' 1994; 41(3): 275-84.]</ref><ref>[https://www.sciencedirect.com/science/article/pii/B9780120597857500478 Callender TJ, Morrow L, Subramanian K, Duhon D, Ristov M. Three dimensional brain metabolic imaging in patients with toxic encephalopathy. ''Environ Res'' 1993; 60(2): 295-319.]</ref><ref>[https://europepmc.org/abstract/med/7778114 Heuser G, Mena I, Alamos F. NeuroSPECT findings in patients exposed to neurotoxic chemicals. ''Toxicol Ind Health'' 1994; 10(4-5): 561-71.]</ref><ref>[https://onlinelibrary.wiley.com/doi/abs/10.1002/hbm.20266 Hillert L, Musabasic V, Berglund H, Ciumas C, Savic I. Odor processing in multiple chemical sensitivity. ''Hum Brain Mapp'' 2006; 28(3): 172-82.]</ref><ref>[https://journals.sagepub.com/doi/abs/10.1177/074823379901500316 Ross GH, Rea WI, Johnson AR, Hickey DC, Simon TR. Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities. ''Toxicol Ind Health'' 1999; 15(3-4): 415-20.]</ref> These abnormalities have been documented both in studies using [[Positron emission tomography]] (PET) and [[Single-photon emission computed tomography]] (SPECT) scans.<ref name=":4" /><ref>[https://link.springer.com/article/10.1007/s10548-015-0453-3 Alessandrini M, Micarelli A, Chiaravalloti A, et al. Involvement of Subcortical Brain Structures During Olfactory Stimulation in Multiple Chemical Sensitivity. ''Brain Topogr 2'' 016; 29(2): 243-52.]</ref><ref>[https://link.springer.com/article/10.1007/s00259-014-2969-2 Chiaravalloti A, Pagani M, Micarelli A, et al. Cortical activity during olfactory stimulation in multiple chemical sensitivity: a (18)F-FDG PET/CT study. ''Eur J Nucl Med Mol Imaging'' 2015; 42(5): 733-40]</ref>

In addition to people with MCS having documented neurological abnormalities, neuroplasticity is thought by some researchers to be an important mechanism in the disease. In 2018, a representative of the Royal Australasian College of Physicians said: “It could be a multiple chemical sensitivity phenomenon. It could be an irritable bowel phenomenon. It could be fibromyalgia... The common unifying features in all of these conditions is related to what we do know is happening, which is neuroplasticity in the nervous system. We know that, regardless of the initiating trigger—whether it was an overwhelming infection of a mould related organism or some other viral infection—it sets up, within the biological system called the nervous system, neuroplastic changes. They can be, and have been, documented by evidence based research. We can document that there are changes in the nervous system, and that change in the nervous system results in a change in the sensitivity and responsiveness of the human being.”<ref name="Hansard9Aug2018">{{citation|url=https://parlinfo.aph.gov.au/parlInfo/download/committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/toc_pdf/Standing%20Committee%20on%20Health,%20Aged%20Care%20and%20Sport_2018_08_09_6406_Official.pdf;fileType=application%2Fpdf#search=%22committees/commrep/e7694a12-573a-4e51-933d-46fe0f9a9a3d/0001%22|title=Biotoxin related illnesses in Australia, comments by Dr Graeme Edwards, Official Committee of the House of Representatives Standing Committee on Health, Aged Care and Sport|date=Aug 9, 2018|location=Canberra|publisher=House of Representatives, Hansard Records}}</ref>{{Rp|12}}<ref name=":40" />

===Immunological===
MCS is not an allergy, and subjects with MCS having adverse reactions do not routinely exhibit the immune markers associated with allergies.<ref name="NICNAS" />{{Rp|21}} Nevertheless, certain immune irregularities have been identified in subjects with MCS in a range of studies.<ref name="Rossi2018" /><ref name=":4" /><ref name="NICNAS" />{{Rp|22}}

In the 1980s and 1990s, some researchers hypothesized that these immune irregularities suggested that MCS was caused by a chemically induced disturbance of the immune system, which resulted in chronic immune dysfunction.<ref name="NICNAS" />{{Rp|22}}<ref name="Genuis2013" /> While others concluded that allergic or immunotoxicological reactions could be contributing factors in at least a subset of MCS patients.<ref name="NICNAS" />{{Rp|22}}<ref>Albright JF, Goldstein RA. Is there evidence of an immunologic basis for multiple chemical sensitivity? Toxicol Ind Health 1992; 8(4): 215-9.</ref><ref>Meggs WJ (1992) MCS and the immune system. Toxicol Ind Health 8(4):203-214.</ref> As more studies were conducted, however, some argued that there was no consistent pattern of immunological reactivity or abnormality in MCS.<ref name="NICNAS" />{{Rp|22}}<ref name="Graveling1999" /><ref>[https://link.springer.com/article/10.1023/A:1026460726965 Labarge XS & McCaffrey RJ (2000) Multiple chemical sensitivity: a review of the theoretical and research literature. Neuropsychol Rev 10(4):183-211.]</ref>

More recently, a French study found that subjects with MCS had higher levels of histamine than controls.<ref name=":4" /><ref name=":26">[https://www.degruyter.com/view/j/reveh.2015.30.issue-4/reveh-2015-0027/reveh-2015-0027.xml Belpomme D, Campagnac C, Irigaray P. Reliable disease biomarkers characterizing and identifying electrohypersensitivity and multiple chemical sensitivity as two etiopathogenic aspects of a unique pathological disorder. Rev Environ Health 2015; 30(4): 251-71.]</ref> It also identified damage to the blood-brain barrier in MCS subjects, the production of antibodies against myelin and evidence of inflammatory processes involving the limbic system and thalamus.<ref name=":4" /><ref name=":26" /> These findings led the research team to conclude that some level of immune activation was likely occurring in the condition.<ref name=":4" /><ref name=":26" />

There is also evidence that subjects with MCS are more likely than controls to have real allergies<ref name="Valderrama2015" />{{Rp|16}} and autoimmune diseases. And the 2019 consensus on MCS notes an association between the condition and [[Hashimoto's thyroiditis|Hashimoto's Thyroiditis]], [[Systemic lupus erythematosus|Systemic Lupus Erythematosus (SLE)]], [[psoriasis]] and atopic [[eczema]].<ref>{{citation|trans-chapter =3.11 Rheumatological evaluation|chapter=3.11|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref><ref>[https://www.ncbi.nlm.nih.gov/pubmed/20588228 Hybenova M, Hrda P, Prochazkova J, Stejskal V, Sterzl I. The role of environmental factors in autoimmune thyroiditis. Neuro Endocrinol Lett 2010; 31(3): 283-9.]</ref><ref>[https://ehp.niehs.nih.gov/doi/abs/10.1289/ehp.97105s2417 Ziem G, McTamney J. Profile of patients with chemical injury and sensitivity. Environ Health Perspect 1997; 105 Suppl 2: 417-36.]</ref><ref>[https://europepmc.org/abstract/med/17594860 Nogué S, Fernandez-Sola J, Rovira E, Montori E, Fernandez-Huerta JM, Munne P. Multiple chemical sensitivity: study of 52 cases. Med Clin (Barc) 2007; 129(3): 96-8; quiz 9.]</ref>

=== Psychological ===
It has also been hypothesized that multiple chemical sensitivity is a psychological disorder. Psychsomatic, psychiatric and psychological theories of MCS, however, have not been accepted by the most recent medical consensus document on MCS,<ref name="Ch2" /> and the hypothesis that MCS has a psychological cause has attracted considerable criticism.<ref name=":7" /><ref name=":4" /><ref name="Genuis2013" /><ref>[https://journals.lww.com/joem/FullText/2018/08000/Multiple_Chemical_Sensitivity___Review_of_the.23.aspx Tuuminen, Tamara "Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives" Journal of Occupational and Environmental Medicine: August 2018 - Volume 60 - Issue 8 - p e429 doi: 10.1097/JOM.0000000000001369]</ref><ref name="Davidoff1994" /><ref>[https://www.mdpi.com/548534 Bransfield RC, Friedman KJ. Differentiating Psychosomatic, Somatopsychic, Multisystem Illnesses, and Medical Uncertainty. ''Healthcare'' (Basel). 2019 Oct 8;7(4). pii: E114. doi: 10.3390/healthcare7040114.]</ref><ref name="SBS">Cunich, Simon. [https://www.sbs.com.au/news/the-feed/mcs-the-condition-that-affects-one-million-australians-but-is-dismissed-by-doctors MCS--the condition that affects one million Australia] SBS television. Sydney, Australia. Updated 14 Aug 2018. [ Is multiple chemical sensitivity real? / Is MCS real?] Prof. Anne Steinemann of Melbourne University: ''"MCS is a very real physical disease".''</ref><ref name="Davidoff1996" />

The main arguments used to support the is that MCS has psychological causes have been:
# there is no certainty about biological causes of MCS, therefore it must be psychological<ref>{{Cite journal|last=Gots|first=Ronald E.|date=1995-01-01|title=Editorial Commentary: Multiple Chemical Sensitivities–Public Policy|url=https://doi.org/10.3109/15563659509000459|journal=Journal of Toxicology: Clinical Toxicology|volume=33|issue=2|pages=111–113|doi=10.3109/15563659509000459|issn=0731-3810|pmid=7897748}}</ref><ref>{{citation|first =Kimberly|last=Hainge|url=https://www.ncagr.gov/SPCAP/pesticides/UpdateFall03.pdf|work=Pesticide Update|publisher=Florida Department of Agriculture & Consumer Services|volume=XXI|issue=1|date=Fall 2003|title=Multiple chemical sensitivity}}</ref>
# that nocebo responses may operate in MCS,<ref>{{Cite journal|last=Binkley|first=K|author-link=|last2=Kutcher|first2=S|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Apr 1997|title=Panic response to sodium lactate infusion in patients with multiple chemical sensitivity syndrome|url=https://doi.org/10.1016/s0091-6749(97)70086-1|journal=Journal of Allergy and Clinical Immunology|volume=99|issue=4|pages=570–574|doi=10.1016/s0091-6749(97)70086-1|issn=0091-6749|pmc=|pmid=|access-date=|quote=|via=}}</ref> and
# that people with MCS are more likely than controls to have anxiety, depression and the personality trait absorption.<ref>[https://doi.org/10.1016%2Fs0091-6749%2897%2970086-1 10.1016/s0091-6749(97)70086-1 Witthöft M, Rist F, Bailer J (2008). "Evidence for a specific link between the personality trait of absorption and idiopathic environmental intolerance". ''J. Toxicol. Environ. Health Part A''. '''71''' (11–12): 795–802. doi: 10.1080/15287390801985687. PMID 18569578]</ref><ref>[http://www.psychosomaticmedicine.org/cgi/pmidlookup?view=long&pmid=16314597 Bailer J, Witthöft M, Paul C, Bayerl C, Rist F (2005). "Evidence for overlap between idiopathic environmental intolerance and somatoform disorders"]. ''Psychosom Med''. '''67''' (6): 921–9. doi: 10.1097/01.psy.0000174170.66109.b7. PMID 16314597]</ref>
The 2019 Italian consensus on MCS concluded that the studies that hypothesize that the condition has a psychological cause "have been the object of strong criticism, both for methodological deficiencies as well as for the conflict of interests of the scientists who propose this thesis."<ref name=":4" /> It said there was consensus that MCS reactions could cause psychiatric symptoms through biological processes (eg. neurogenic inflammation) and that symptoms of the condition should not be mistaken for the cause.<ref name=":4" /> It also highlighted that "it was researchers at Johns Hopkins University who pointed out that it is ineffective to use personality tests such as MMP2 (i.e. Minnesota Multiphasic Personality Inventory 2) for the study of the pathogenesis of environmental diseases...concluding that the presence of psychological-psychiatric symptoms in patients with MCS was compatible with the objective limitations imposed by the disease, rather than being the cause."<ref name=":4" /><ref name="Davidoff1994">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Fogarty|first2=L.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Sep 1994|title=Psychogenic origins of multiple chemical sensitivities syndrome: a critical review of the research literature|url=https://www.ncbi.nlm.nih.gov/pubmed/7944561|journal=Archives of Environmental Health|volume=49|issue=5|pages=316–325|doi=10.1080/00039896.1994.9954981|issn=0003-9896|pmc=|pmid=7944561|access-date=|quote=|via=}}</ref><ref name="Davidoff1996">{{Cite journal|last=Davidoff|first=A. L.|author-link=|last2=Keyl|first2=P. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=May 1996|title=Symptoms and health status in individuals with multiple chemical sensitivities syndrome from four reported sensitizing exposures and a general population comparison group|url=https://www.ncbi.nlm.nih.gov/pubmed/8687241|journal=Archives of Environmental Health|volume=51|issue=3|pages=201–213|doi=10.1080/00039896.1996.9936017|issn=0003-9896|pmc=|pmid=8687241|access-date=|quote=|via=}}</ref>

Other researchers have emphasized that the psychosocial impacts of the disease (especially isolation and stigmatization) are likely to have significant impacts on mental health.<ref name=":7" />{{Rp|48}}<ref name="Davidoff1996" /><ref name="Davidoff1994" /><ref>[http://downloads.hindawi.com/journals/isrn.nursing/2011/838930.pdf Gibson PR, Lindberg A. Physicians' perceptions and real practices regarding patient reports of multiple chemical sensitivity. ISRN Nurs 2011; 2011: 838930.]</ref><ref name="Gibson2009" /><ref>"MCS and EI [Multiple Chemical Sensitivities and Environmental Illness]", [https://counselingatcela.com/ The Counseling Center at CELA] blog. "Is MCS a mental illness? MCS is not a mental illness." Accessed 18 Feb 2020.</ref><ref name="PMC2821254">{{Cite journal|last=Lavergne|first=M. Ruth|author-link=|last2=Cole|first2=Donald C.|author-link2=|last3=Kerr|first3=Kathleen|author-link3=|last4=Marshall|first4=Lynn M.|author-link4=|date=Feb 2010|title=Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity|url=https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2821254/|journal=Canadian Family Physician|volume=56|issue=2|pages=e57–e65|doi=|issn=0008-350X|pmc=2821254|pmid=20154232|access-date=|quote=|via=}}</ref> One study showed that anxiety and depression typically started in people with MCS post onset of the condition.<ref name="Caress2003">{{Cite journal|last=Caress|first=Stanley M|author-link=|last2=Steinemann|first2=Anne C|author-link2=|date=2003-09-01|title=A review of a two-phase population study of multiple chemical sensitivities.|url=https://ehp.niehs.nih.gov/doi/10.1289/ehp.5940|journal=Environmental Health Perspectives|volume=111|issue=12|pages=1490–1497|doi=10.1289/ehp.5940|pmc=1241652|pmid=12948889|access-date=|quote=The study found that while 37.7% of respondents said that they experienced mental health symptoms after developing sensitivities; only 1.4% (n =1) said that they had had mental health problems prior to becoming sensitive, and 5.8% said they didn’t know whether they had had mental health problems prior.|via=}}</ref>

The presence of [[nocebo]] responses in MCS does not indicate that it is the cause of the disease.<ref>''[http://eceri-institute.org/fichiers/1441982765_Statement_EN_DEFINITIF.pdf Brussels International Scientific Declaration on EHS and MCS] (2015).'' Declaration from the 5th Paris Appeal Congress of 18 May 2015 at the Royal Academy of Medicine, Brussels, Belgium. ''"The nocebo effect is not a relevant nor a valid explanation when considering scientifically valuable blind provocation studies, since objective biological markers are detectable in patients as well as in animals."'' </ref> Nocebo responses are found in many biologically caused conditions,<ref>{{citation|url =https://www.health.harvard.edu/newsletter_article/The_nocebo_response|title = The nocebo response|website=Harvard Health. Harvard Medical School blog|date =Mar 2014|access-date=Feb 12, 2020}}</ref> including asthma, and they have been shown to be especially pronounced in neurological conditions (including [[migraine]] and chronic pain).<ref>{{Cite journal|last=Bittar|first=Caroline|author-link=|last2=Nascimento|first2=Osvaldo J. M.|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|date=Jan 2015|title=Placebo and nocebo effects in the neurological practice|url=https://www.ncbi.nlm.nih.gov/pubmed/25608129|journal=Arquivos De Neuro-Psiquiatria|volume=73|issue=1|pages=58–63|doi=10.1590/0004-282X20140180|issn=1678-4227|pmc=|pmid=25608129|access-date=|quote=|via=}}</ref>

It is noteworthy that psychological approaches to care in MCS patients have had “very limited success,”<ref name=":7" />{{Rp|48}} and that neither MCS, MCS/ES nor IEI have been included in any edition of the DSM (''American Psychiatric Association Diagnostic and Statistical Manual''<ref>{{Cite book|title=Diagnostic and Statistical Manual of Mental Disorders (DSM-5)|pages=|isbn=978-0890425541|edition=5th|volume=|language=|title-link=|url=|access-date=|date=May 15, 2014|publisher=American Psychiatric Association|last=American Psychiatric Association|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref>) nor have they been listed among somatoform disorders in the [[ICD-10|International Classification of Diseases]].<ref>[https://www.icd10data.com/ICD10CM/Codes/F01-F99/F40-F48/F45-/F45.8 "Other somatoform disorders". 2020 ICD-10-CM Diagnosis Code F45.8]</ref>

In Canada, in 2017, following a three-year government inquiry into environmental illness, it was recommended that a public statement be made by the health department dispelling the misperception that MCS/ES is psychological.<ref name=":7" />{{Rp|17}}

=== Genetic ===
The 2019 consensus on MCS said that the condition could, at least in part, be caused by genetic alterations affecting detoxification pathways—something which in combination with toxin exposures could make some people more vulnerable to developing MCS than the rest of the population.<ref name=":4" />

Recent Italian studies found that compared to controls, patients with MCS had higher levels of the nitrites and nitrates that are involved in oxidative stress and inflammatory processes, including those that contribute to the oxidative damage of DNA.<ref name=":4" /> They also found that the presence of the following genetic polymorphisms were more likely in people with MCS than controls: NOS3, NOS2 and GPX1.<ref name=":4" /><ref name=":23">[https://www.hindawi.com/journals/mi/2015/245308/abs/ De Luca C, Gugliandolo A, Calabro C, et al. Role of polymorphisms of inducible nitric oxide synthase and endothelial nitric oxide synthase in idiopathic environmental intolerances. Mediators Inflamm 2015; 2015: 245308.]</ref><ref name=":24">[https://www.sciencedirect.com/science/article/pii/S0024320515301211 Gugliandolo A, Gangemi C, Calabro C, et al. Assessment of glutathione peroxidase-1 polymorphisms, oxidative stress and DNA damage in sensitivity-related illnesses. Life Sci 2016; 145: 27-33. 78.]</ref>

Other genetic markers known to affect detoxification pathways have been identified as being more common in subjects with MCS than controls,<ref name=":4" /><ref name=":23" /><ref name=":24" /><ref name="DeLuca2011">[https://www.mdpi.com/1660-4601/8/7/2770 De Luca C, Raskovic D, Pacifico V, Thai JC, Korkina L. The search for reliable biomarkers of disease in multiple chemical sensitivity and other environmental intolerances. Int J Environ Res Public Health 2011; 8(7): 2770-97.]</ref><ref>[http://downloads.hindawi.com/journals/oximed/2013/831969.pdf Caccamo D, Cesareo E, Mariani S, et al. Xenobiotic sensor- and metabolism related gene variants in environmental sensitivity-related illnesses: a survey on the Italian population. Oxid Med Cell Longev 2013; 2013: 831969.]</ref><ref>[https://www.hindawi.com/journals/mi/2014/924184/abs/ De Luca C, Thai JC, Raskovic D, et al. Metabolic and genetic screening of electromagnetic hypersensitive subjects as a feasible tool for diagnostics and intervention. Mediators Inflamm 2014; 2014: 924184.]</ref> including polymorphisms and differences in expression of the following: [[CYP2D6]], [[MTHFR]], [[NAT1]], [[NAT2]], [[GSTM1]], and [[PON1]] and [[PON2]].<ref>{{Cite web|url=https://www.karger.com/Article/FullText/497322|title=Assessment of CYP2C9, CYP2C19, and CYP2D6 Polymorphisms in Allergic Patients with Chemical Sensitivity|last=D’Attis|first=S|authorlink=|last2=Massari|first2=S|authorlink2=|date=2019|website=|pages=173–186|doi=10.1159/000497322|archive-url=|archive-date=|access-date=2020-05-14|last3=Mazzei|first3=F|last4=Maio|first4=D|last5=Bozzetti|first5=MP|last6=Vergallo|first6=I|last7=Mauro|first7=S|last8=Minelli|first8=M|journal=Int Arch Allergy Immunol|volume=179|issue=}}</ref><ref name="McKeown et al. 2004">{{cite journal |vauthors=McKeown-Eyssen G, Baines C, Cole DE, Riley N, Tyndale RF, Marshall L, Jazmaji V | title = Case-control study of genotypes in multiple chemical sensitivity: CYP2D6, NAT1, NAT2, PON1, PON2 and MTHFR | volume = 33| issue = 5 | pages = 971–8 | pmid = 15256524 | doi = 10.1093/ije/dyh251 | journal = Psychosomatic Medicine |url=https://doi.org/10.1093%2Fije%2Fdyh251|last=|first=|last2=|first2=|date=2004|pmc=|quote=|last3=|first3=|last4=|first4=|last5=|first5=|last6=|first6=|last7=|first7=|last8=|first8=|author-link=|author-link2=|author-link3=|author-link4=|author-link5=|author-link6=|via=}}</ref><ref name="Schnackenberget">{{Cite journal|last=Schnakenberg|first=Eckart|last2=Fabig|first2=Karl-Rainer|last3=Stanulla|first3=Martin|last4=Strobl|first4=Nils|last5=Lustig|first5=Michael|last6=Fabig|first6=Nathalie|last7=Schloot|first7=Werner|date=2007-02-10|title=A cross-sectional study of self-reported chemical-related sensitivity is associated with gene variants of drug-metabolizing enzymes|url=https://doi.org/10.1186/1476-069X-6-6|journal=Environmental Health|volume=6|issue=1|pages=6|doi=10.1186/1476-069X-6-6|issn=1476-069X}}</ref>

These findings could support the hypothesis that MCS is caused by a synergy of environmental exposures to toxic substances and the impaired ability to metabolize toxic substances, due to factors related to genetic predisposition.<ref name=":4" />

== Recognition ==
In 1996, an expert panel at [[World Health Organization|WHO]]/ICPS (International Classification for Patient Safety) was set up to examine MCS.<ref name=":45" /> The panel:
# "accepted the existence of a disease of unclear pathogenesis",
# proposed that the disease was acquired, that its symptoms were "in close relationship to multiple environmental influences, which are well tolerated by the majority of the population," and that it "could not be explained by a known clinical or psychic disorder,"
# suggested that the broader term "idiopathic environmental intolerances" (IEI) be adopted instead of MCS, to incorporate MCS and several other conditions under a single umbrella term.<ref name=":45" />
MCS is not included as a separate, discrete disease by the [[World Health Organization]]'s (WHO) index of diseases (ICD-11). However, existing disease codes in the ICD-10 can be used for MCS, including:
# '''J68.9''': unspecified respiratory conditions due to inhalation of fumes, gas, and chemical vapors; and
# '''T78.4''': unspecified allergies (allergic reaction Nitrous Oxide System (NOS)-hypersensitivity NOS-idiosyncrasy NOS)."<ref name="Rossi2018" />{{Rp|139}}

In the '''ICD-10-DM''' and '''ICD-10-SGB-V''', [[Germany|Germany's]] adaptions of the ICD-10, multiple chemical sensitivity is recognized as a chemical hypersensitivity or intolerance (''Chemical-Sensitivity[MCS]-Syndrom, Multiple-'') under the code '''T78.4;''' this is also in use in [[Austria]].<ref>{{Cite book|title=ICD-10-GM Version 2012 : internationale statistische Klassifikation der Krankheiten und verwandter Gesundheitsprobleme|pages=184|isbn=978-3-7691-3481-0|edition=2012|volume=|language=de|title-link=|url=https://books.google.co.uk/books?id=E2Sy_nN0O8sC&lpg=PT53&ots=dgNsEl1meY&dq=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&pg=PT53#v=onepage&q=%C3%9Cberempfindlichkeit%20T78.4%20multiple%20chemical%20sensitivity&f=false|access-date=|date=2011|publisher=Deutscher Ärzteverlag|last=World Health Organization|first=|author-link=World Health Organization|last2=DIMDI|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|author-link7=|last8=|first8=|author-link8=|last9=|first9=|author-link9=|veditors=|others=|doi=|oclc=|quote=|archive-url=|archive-date=|location=|editor-last=|editor-first=|editor1-link=|editor-last2=|editor-first2=}}</ref><ref name="Rossi2018" /> Japan also recognizes MCS as a separate disease.<ref name="Rossi2018" />{{Rp|139}}<ref name=":10" /><ref name=":41">{{Cite book|isbn=978-0-9807221-4-7|url=http://test.nicnas.gov.au/Media/Latest_News/MCS.asp|title=A Scientific Review of Multiple Chemical Sensitivity: Identifying Key Research Needs|date=2010|last=National Industrial Chemicals Notification and Assessment Scheme|last2=Office of Chemical Safety and Environmental Health|location=Canberra, Australia|page=15|url-status=dead|archive-date=Nov 2010|archive-url=https://web.archive.org.au/awa/20160615131255mp_/https://www.nicnas.gov.au/__data/assets/word_doc/0015/17223/MCS-Final-Report-for-publication-November-2010-hardcopy-version.docx|chapter=2.5 Does MCS have a disease classification?|quote=Recognition of MCS as a disease and disability...In [[Germany]], MCS is included in the alphabetical index of the German version of the International Statistical Classification of Diseases and Related Health Problems (ICD-10-SGB-V), first published in November 2000 by the German Institute of Medical Documentation and Information (DIMDI). At this stage, [[Austria]] has adopted the German ICD-10 for its use and therefore MCS is included also in the Austrian ICD-10}}</ref> And in some countries, like [[Sweden]], chemical sensitivities are classified as a form of sensory hyperreactivity (CSS-SHR).<ref name="Steinemann2018" />

And as mentioned [[Multiple chemical sensitivity#MCS in ME and ME.2FCFS|above]], chemical sensitivities are recognized symptoms of ME/CFS. In 2018, the U.S. [[Centers for Disease Control and Prevention|Centers for Disease Control and Prevention]] (CDC) said that ME/CFS patients can have sensitivities to chemicals.<ref name="CDC-MECFS">{{Cite web|url=https://www.cdc.gov/me-cfs/symptoms-diagnosis/symptoms.html|title=Symptoms of ME/CFS {{!}} Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS)|last=Centers for Disease Control|first=|authorlink=Centers for Disease Control and Prevention|last2=|first2=|authorlink2=|date=2019-11-19|website=[[Centers for Disease Control]]|language=en-us|archive-url=|archive-date=|access-date=2020-05-14}}</ref>

== History ==
In 1956, American allergist Dr. Theron G. Randolph coined the term "environmental illness," to describe symptoms and disorders he observed in some of his patients after they were exposed to various unrelated chemical compounds.<ref name=":41" /><ref name=":45">{{Cite journal|last=Schwenk|first=Michael|date=2004|title=Multiple Chemical Sensitivity (MCS) - Scientific and Public-Health Aspects|url=https://www.ncbi.nlm.nih.gov/pubmed/22073047|journal=GMS current topics in otorhinolaryngology, head and neck surgery|volume=3|pages=Doc05|issn=1865-1011|pmc=3199799|pmid=22073047}}</ref>

Then in 1987, Dr. Mark R. Cullen, also an American allergist, introduced the term MCS in journals of occupational medicine. He proposed that MCS described: an acquired disorder, characterized by recurrent symptoms, affecting multiple organs and systems, which arose in response to a demonstrable exposure to chemicals, even for low doses, much lower than those causing reactions in the general population.<ref name=":41" /><ref name=":45" />

Two years later, an international multidisciplinary team of 89 clinicians and researchers commenced a study into MCS, which culminated in the first real international consensus on the condition being agreed upon and published in ''The Archives of Environmental Health'' in 1999.<ref name="Rossi2018" /><ref name="pmid10444033" />

In 1996, an expert panel of the World Health Organization/International Classification for Patient Safety (WHO/ICPS) accepted the existence of MCS as a health condition with a cause unknown, and suggested that it be called "idiopathic environmental intolerances"(IEI), a term that incorporates a number of conditions sharing similar symptoms.<ref name=":45" />

In May 2019, the Italian Workgroup on MCS, a group of physicians, research scientists and clinical staff, published a detailed, 30-page consensus paper called the ''Italian Consensus on MCS.''<ref name="ItalianConsensus">{{citation|url=https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf|title=Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS|trans-title=Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS) by the Italian Workgroup on MCS|last=Grouppo di Italiano Studio MCS|location=Università degli Studi di Milano, Italy|date=2019-05-23}}</ref> This document may be the most detailed scientific review of research about MCS to date. It goes into detail about ways the condition can be better managed in clinical environments, particularly in hospitals. The workgroup published their consensus in Italian and English, asking for input from MDs and other health professionals, biologists and chemists. At the time of writing, the response to the consensus had not been published.

== Controversy ==
MCS sufferers and the physicians treating them have been subject to campaigns aimed at undermining the veracity of the condition.<ref>{{Cite book|title=Merchants of Doubt: How a Handful of Scientists Obscured the Truth on Issues from Tobacco Smoke to Climate Change|pages=|isbn=|edition=2nd|volume=|language=|title-link=|url= https://books.google.com/books/about/Merchants_of_Doubt.html?id=CrtoNFTuPwwC |access-date=|date=2011|publisher=Bloomsbury|last=Oreskes|first=Naomi|author-link=|last2=Conway|first2=Erik M.|author-link2=|quote=|archive-url=|archive-date=|location=}}</ref> This has played out in academia and in the media—and, perhaps with the greatest impact on sufferers, on Wikipedia.<ref name="Deadline201908">[https://deadline.com/2019/08/netflix-sued-affliction-documentary-defamation-fraud-1202664068/ Netflix Sued For Defamation By 'Afflicted' Subjects Who Say Docuseries Painted Them As "Crazy Hypochondriacs". Deadline. Aug 17, 2019. Quote: ''"a salacious reality television program that questioned the existence of their chronic illnesses and portrayed Plaintiffs as lazy, crazy, hypochondriacs and/or malingerers who were deserving of scorn and who in fact have received scorn and abuse because of Defendants’ cruel and duplicitous actions.”'']</ref><ref name="Dusenberry">Dusenberry, Maya. [https://psmag.com/social-justice/an-open-letter-accuses-netflixs-afflicted-of-abandoning-ethics-and-science An open letter accuses Netflix's ''Afflicted'' of abandoning ethnics and science]. PS Mag. 20 Sep 2018. quote=The Netflix series Afflicted promised compassion for sufferers of poorly understood chronic illnesses. Instead, it peddled the tired narrative that their suffering is "all in their heads...I joined a group of physicians, scientists, filmmakers, and writers—including Lena Dunham, Monica Lewinsky, and Mario Carpecchi, a Nobel Laureate in genetics—in signing an open letter to Netflix detailing many ethical missteps, scientific errors, and omissions evident in the series. Allowing Afflicted to remain on the widely watched platform, the letter states, 'will reinforce barriers to appropriate medical care...and add to the stigma and social isolation of an already profoundly marginalized group of people.'"'']''</ref><ref>{{Citation|title=Talk page of Wikipedia's multiple chemical sensitivity page|url= https://en.wikipedia.org/wiki/Talk%3AMultiple_chemical_sensitivity|access-date=Feb 12, 2020}}</ref><ref name="capturedbysk" /><ref>[http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/ Wikipedia captured by skeptics] Skeptics about skeptics blog. Accessed Feb 12, 2020. ''"Wikipedia currently is the area in which dogmatic skeptics are most successful and influential. One of these activist groups is called Guerrilla Skepticism on Wikipedia, founded by Susan Gerbic. Another leader of the online skeptical movement is Tim Farley, who runs the website Skeptical Software Tools...The Wikipedia skeptics work in teams (contrary to Wikipedia rules) and most are well trained."''</ref><ref>{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/rampant-harassment-on-wikipedia/|title=Rampant Harassment on Wikipedia|last=Skeptical About Skeptics|first=|authorlink=|last2=|first2=|authorlink2=|date=|website=Skeptical About Skeptics|language=en-US|archive-url=|archive-date=|access-date=2020-02-12}}</ref><ref name="Bundrant2015">{{Citation|last=Bundrant|first= Mike|url=http://wikipediawarning.com/top-6-things-wikipedia-health-editors-have-told-me/|title =Top 6 Things Wikipedia Health Editors Have Told Me Since Announcing the Book that Challenges Wiki Bias|website=WikiWarn blog|date =Apr 15, 2015|access-date= Feb 12, 2020}}
</ref><ref name="greenmed">{{Cite web|url =https://www.greenmedinfo.com/blog/rise-and-fall-wikipedia|title =The rise and fall of Wikipedia|last =Orthomolecular News Service|website=Greenmedinfo blog|date=Sep 30, 2020|access-date =Feb 12, 2020}}</ref> These efforts have created a perception that MCS is a controversial or disputed condition,<ref name="SBS" /><ref name="spurious" /> which is not supported by recent academic reviews of MCS research.<ref name="Ch1" /><ref name=":7" /><ref name="Rossi2018" /><ref name="pmid30088144" /><ref name="DeLuca2011" />

Some say chemical industry interest groups have funded these efforts, and indeed some of the most vocal writers with anti-MCS stances have also been industry-paid expert witnesses in legal cases involving alleged chemical injuries.<ref>[https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/ Arizona Centre for Advanced Medicine. Multiple Chemical Sensitivities (MCS) Under Siege], Jun 26, 2013. Quote: ''"In 1990, the Chemical Manufacturers Association (now the American Chemistry Council) vowed to work to prevent the recognition of MCS out of concern for potential lost profits and increased liability if MCS were to become widely acknowledged (2). It specifically committed to work through physicians and medical associations to accomplish this, stating that it was critical to keep physicians from legitimizing MCS...The industry has enlisted the aid of vocal anti-MCS physicians who promote the myths that people with MCS are “hypochondriacs,” “hysterical,” “neurotic,” suffer from some other psychiatric disorder, belong to a “cult,” or just complain too much. Most of these physicians work for industry as high-paid expert witnesses although their financial ties are usually not disclosed in their journal articles, interviews, or speaking engagements. Therefore, many people, including those in the health care profession, are often led to believe that these physicians’ opinions reflect an honest appraisal of MCS rather than the chemical industry’s agenda. At least one industry expert witness has authored two anti-MCS position papers for prominent medical associations. It is easy to see why these papers are biased against MCS and how by helping to combat MCS in the courts, these position statements are quite lucrative for industry and expert witnesses alike."''</ref>

The blogs Quackwatch and Science-Based Medicine (SBM)—related blogs dominated by the same brand of skepticism—are two groups known to have repeatedly published criticism about MCS's recognition as a medical condition, claiming MCS was a "bogus", "fad" or "spurious" diagnosis.<ref name="capturedbysk">{{citation|last =Gale|first =Richard|last2 = Null|first2=Gary|title=Can we trust Wikipedia and its medical skepticism?|url=http://prn.fm/can-trust-wikipedia-medical-skepticism/|work=Progressive Radio Network|date=Aug 2, 2018|access-date= Feb 12, 2020|quote=This article will challenge a relatively recent group of Skeptics that identify themselves as the advocates of Science-Based Medicine (SBM), which is not to be confused with the widely accepted approach to decision-making in medical practice known as Evidence-Based Medicine (EBM).}}</ref><ref>{{citation|first=Paul R|last =Lees-Haley|title =Propaganda techniques related to enviromental scares. This article was adapted from Lee-Haley PR. ''Manipulation of perception in mass tort litigation''. 1997|publisher=Quackwatch blog|date=Mar 10, 1998}}</ref><ref name="Gavura">{{citation|last =Gavura|first=Scott|title=Multiple Chemical Sensitivity: Separating facts from fiction|quote='Does multiple chemical sensitivity exist?' The symptoms certainly do, but it’s less clear if they are due to “chemicals.”|publisher=Science-based medicine blog|date =Jul 3, 2014}}</ref><ref>{{citation |last =Lees-Haley|first =Paul R.|title =Mold Neurotoxicity: Validity, Reliability and Baloney|publisher=Quackwatch blog|date=Dec 23, 2002}}</ref><ref>{{citation |title =Multiple chemical sensitivity suffering is real, diagnosis isn't--Quackbusters"|work=Probe Newsletter|issue=07-03|date =Jan 1, 1999}}</ref><ref>{{citation |last=Hall|first=Harriet|title =Environmental Medicine – Not Your Average Specialty|publisher=Blog: Science-based medicine: Exploring issues and controversies in science and medicine|quote=Rea is best known for his promotion of the concept of multiple chemcial sensitivity (MCS), a diagnosis not recognized by the scientific community}}</ref><ref>{{citation |last =MacBeth|first=Braden|title =Afflicted and the Tragedy of Fake Illnesses|date =Nov 26, 2018}}</ref> Quackwatch's founder, retired psychiatrist Stephen Barrett, has personally written prolifically on the subject of MCS.<ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Questionable Organizations: An Overview|date=Oct 20, 2019|quote=The American Academy of Environmental Medicine, which promotes "clinical ecology" and the bogus concept of multiple chemical sensitivity.}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Vulnerability to Quackery|date=Jan 16, 2019}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title=Regulatory Actions against AAEM Members|publisher=Quackwatch blog|date=Nov 23, 2016|quote=The American Academy of Environmental Medicine (AAEM), which was founded by Theron Randolph in 1965 as the Society for Clinical Ecology... most AAEM members espouse dubious concepts of multiple chemical sensitivity, toxic mold...|url-status=dead}}</ref><ref>{{Citation |last=Barrett|first=Stephen|title= The Bogus Connection between "MCS" and Porphyria|publisher=Quackwatch blog|date=Jan 22, 2010}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=MCS Proclamations}}
</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|first2=Ronald E|last2=Gots|title=Gulf War Syndrome|quote=Some sufferers claim to have multiple chemical sensitivity (MCS)}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Be Wary of "Fad" Diagnoses|date=Oct 6, 2018}}</ref><ref>{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Index to "Fad" Diagnoses. What Is a "Fad" Diagnosis?|date=Mar 28, 2019}}</ref><ref>{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=A Close Look at "Multiple Chemical Sensitivity"|date=1998}}</ref><ref name="resolution21">{{Citation |last=Barrett|first=Stephen|publisher=Quackwatch blog|title=An Analysis of the National Environmental Justice Advisory Council Enforcement Subcommittee's Resolution #21 on Multiple Chemical Sensitivity|date=Oct 16, 2000}}</ref><ref name="Gavura" /><ref name="spurious">{{Citation|last=Barrett|first=Stephen|publisher=Quackwatch blog|title=Multiple Chemical Sensitivity: A Spurious Diagnosis|date=Nov 23, 2016}}</ref>

Important contexts for these efforts are that: (1) legal actions—including defamation suits in the U.S.—have alleged that Quackwatch and Barrett have been actively and knowingly promoting inaccurate information on a range of medical conditions on Wikipedia<ref>{{citation|url=https://www.casewatch.net/civil/null/wikipedia/amended_complaint.pdf|title=Amended complaint against WIKIPEDIA to the Supreme Court of the State of New York, Country of New York|date=Nov 24, 2009}}</ref><ref name=":31">{{Citation|url=http://www.skepticalaboutskeptics.org/wikipedia-captured-by-skeptics/|title=Wikipedia » Skeptical About Skeptics|website=Skeptical About Skeptics|language=en-US|access-date=2020-02-19}}</ref><ref name=":20">{{citation|last =Gale|first =Richard|title=Stephen Barrett: Wikipedia's Agent Provocateur against natural medicine|url =http://prn.fm/stephen-barrett-wikipedias-agent-provacateur-natural-medicine/|work=Progressive Radio Network|date =Apr 1, 2019}}</ref> (of note, in 2003, a California Appeals Court, for example, found Quackwatch's founder “to be biased and unworthy of credibility”<ref>[https://prn.fm/stephen-barrett-medical-mccarthyism/ Stephen Barrett and Medical McCarthyism] The Progressive Radio network blog. Accessed Feb 21, 2020]</ref><ref name=":20" />); and (2) in academia, a 2019 consensus on MCS concluded that the studies that hypothesized MCS was a psychogenic disorder had been the object of strong criticism, in part, for "the conflict of interests of the scientists who proposed this thesis."<ref name=":4" />

While those who have argued that MCS isn't real or is psychologically caused have undoubtedly successfully influenced popular perceptions about the condition,<ref>{{citation |url=https://www.arizonaadvancedmedicine.com/articles/2013/june/multiple-chemical-sensitivities-mcs-under-siege/|website=Arizona Centre for Advanced Medicine|title =Multiple Chemical Sensitivities (MCS) Under Siege|date =Jun 26, 2013}}</ref> their commentaries are at odds with: (1) the current medical consensus about MCS,<ref name="Rossi2018" /><ref name="pmid10444033" /><ref name="pmid30088144" /><ref name=":7" /><ref name="Valderrama2015" />{{Rp|31}}<ref name="Ch2" /><ref name="Hansard9Aug2018" />{{Rp|11}} (2) conclusions of the most recent academic reviews of MCS research in scientific journals,<ref name="Rossi2018" /><ref name="pmid30088144" /> and (3) the recognition of the condition by the WHO/ICPS<ref name=":45" /> and by other national and state health agencies, physicians' organizations and hospitals.<ref name="Rossi2018" /><ref name=":41" /><ref name="IEQP" /><ref name="Valderrama2015" />{{Rp|17}}<ref name=":10" /><ref name=":35" /><ref name=":34" /><ref name=":36" /><ref name=":37" /><ref name=":38" /><ref name=":39" /><ref name="Hansard9Aug2018" />{{Rp|11}}<ref name=":45" /><ref>{{citation|date=2007|title=Australian Human Rights Commission Access: Guidelines and information|last=Australian Human Rights and Equal Opportunity Commission|location= Canberra|url=http://www.humanrights.gov.au/publications/access-guidelinesand-information#chem}}</ref><ref name="Hu2018">[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5999262 Hu, Howard, Banes Cornelia (2018) “Recent insights into 3 underrecognized conditions: Myalgic encephalomyelitis–chronic fatigue syndrome, fibromyalgia, and environmental sensitivities–multiple chemical sensitivity” University of Toronto, Ontario. Canada Family Physician. 2018 Jun; 64(6): 413–415.; PMID: 29898928; PMCID: PMC5999262]</ref><ref name="ILRU">{{citation|last=Michaels|first=Bob|url=https://www.ilru.org/sites/default/files/MCS%20FAQ.pdf|title=Frequently asked questions about multiple chemical sensitivity|website =Independent Living Research Utilization|date=2013|quote= Is MCS real -- or just a psychosomatic, boutique disability? Both MCS and EI are very real conditions...The Social Security Administration and U.S. Department of Housing and Urban Development recognize MCS as a disabling condition, as do numerous other government agencies and judicial bodies.}}</ref>{{See also|Psychologization}}<div role="note" class="hatnote navigation-not-searchable"></div>

==In the media==
===Safe (1995) ===
[[File:Safe.jpg|thumb|Is multiple chemical sensitivity a mental illness? This is a question some critics thought director Todd Haynes was posing in his 1995 film ''Safe.'' The film tells the story of Carol, who suddenly develops a mysterious and unexplained environmental illness, and receives little sympathy from her husband and community. But Haynes said that he used MCS as a metaphor for AIDS, and how AIDS sufferers in the 1980s were regarded and treated.<ref name=":14" /> In the film he explores stigma, alienation and isolation. ]]
''Safe'' is a cult film, by writer and director Todd Haynes, known for its depiction of MCS as a profoundly alienating and destabilizing condition.<ref name=":13">{{Cite web|url=https://www.youtube.com/channel/UCOzFilLNcgrGzAeECAbUFCQ|title="Todd Haynes Q&A {{!}} Safe", Retrospective of Todd Haynes films|last=|first=|date=Nov 25, 2015|website=YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref>

''Safe'' tells the story of Carol White, played by Julianne Moore, a homemaker in Los Angeles, who suddenly develops a range of unexplained symptoms following the renovation of her home. With severe symptoms, which doctors are unable to treat, and a largely indifferent and unsupportive community, Carol ultimately leaves her home and moves to a desert community for people with environmental illness.

“She is so excruciatingly alone,” Moore said of her character at the end of the film.<ref name=":14">{{Cite web|url=https://www.youtube.com/watch?v=EZmjaC8cN10|title=Todd Haynes and Julianne Moore on Safe|last=|first=|date=|website=CriterionCollection, YouTube|archive-url=|archive-date=|access-date=Oct 30, 2019}}</ref> While Haynes said Carol’s isolation was both the answer and the problem for her.<ref name=":13" />

Early in the Corona virus pandemic, Carol's social isolation was compared to the psychosocial experiences of Covid-19 lockdowns<ref name="ammag">{{Cite web|url=https://www.americamagazine.org/arts-culture/2020/04/11/1995-film-safe-has-new-meaning-during-our-coronavirus-isolation|title=The 1995 film ‘Safe’ has new meaning during our coronavirus isolation|last=Di Corpo|first=Ryan|authorlink=|last2=|first2=|authorlink2=|date=April 11, 2020|website=|archive-url=|archive-date=|access-date=31 December 2020}}</ref>.{{See also|Safe}}<div role="note" class="hatnote navigation-not-searchable">{{See also|Safe}}</div>

===Afflicted docuseries (2018)===
Netflix's 2018 documentary series [[Afflicted]] features several patients with MCS.

After its release, ''Afflicted'' was accused of misrepresenting patients with chronic illnesses, with several people who featured in the series suing Neflix for defamation.<ref name="Deadline201908" />

An open letter to Netflix, signed by over 40 doctors, medical professionals and patient advocates, accused the media-services provider and production company of presenting flawed medical and scientific information. It also said [[ethical issues|unethical]] journalistic methods were used in the making of the series and called for it to be taken off Netflix.<ref name="Afflictedletter">{{Cite web|url =https://medium.com/@afflicted/open-letter-to-netflix-regarding-the-afflicted-docuseries-d2b5263c9eb6|title =Open Letter to Netflix Regarding the “Afflicted” Docuseries|date=Sep 18, 2018}}</ref>

{{See also|Afflicted}}

==Notable studies and publications==
*1999, Multiple chemical sensitivity: a 1999 consensus<ref name="pmid10444033" /> - [https://semanticscholar.org/paper/5d389fb8a204e089ce22e9cc7720aa8507581c2f (Full text)]
*2018, Multiple Chemical Sensitivity: Review of the State of the Art in Epidemiology, Diagnosis, and Future Perspectives - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5794238/ (Full text)]
* 2018, Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review<ref name="pmid30088144">{{Cite journal|last=Viziano|first1=A.|last2=Micarelli|first2=A.|last3=Pasquantonio|first3=G.
|last4=Della-Morte|first4=D.|last5=Alessandrini|first5=M.|date=Nov 2018|title=Perspectives on multisensory perception disruption in idiopathic environmental intolerance: a systematic review|journal=Int Arch Occup Environ Health|volume=91|issue=8|pages=923–935|doi=10.1007/s00420-018-1346-z|pmid=30088144|url=https://www.ncbi.nlm.nih.gov/pubmed/30088144}}</ref> - [https://www.ncbi.nlm.nih.gov/pubmed/30088144 (Abstract)]
*2019, Italian Consensus on Multiple Chemical Sensitivity (MCS) -- Consensus Document and Guidelines on Multiple Chemical Sensitivity (MCS)<ref name="ItalianConsensus" /> - [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf (Full text - English)]
::Original title: ''Consenso Italiano sulla Sensibilita Chimica Multipla (MCS). Documento di consenso e linee guida sulla Sensibilita Chimica Multipla (MCS) del Gruppo di Studio Italiano sulla MCS'' - [https://www.infoamica.it/wp-content/uploads/2019/07/Consenso-MCS-20-giugno-2019.pdf (Full text - Italian)]
*2016, Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity<ref name="Azuma2019">{{Cite journal|last=|first=|author-link=|last2=|first2=|author-link2=|last3=|first3=|author-link3=|last4=|first4=|author-link4=|last5=|first5=|author-link5=|last6=|first6=|author-link6=|last7=|first7=|last8=|first8=|vauthors=Azuma K, Uchiyama I, Tanigawa M, Bamba I, Azuma M, Takano H, et al.|date=2016-12-09|title=Association of Odor Thresholds and Responses in Cerebral Blood Flow of the Prefrontal Area during Olfactory Stimulation in Patients with Multiple Chemical Sensitivity|url=https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0168006|journal=PLOS ONE|language=en|volume=11|issue=12|pages=e0168006|doi=10.1371/journal.pone.0168006|issn=1932-6203|pmc=|pmid=|access-date=|quote=|via=}}</ref> - [https://doi.org/10.1371/journal.pone.0168006.g005 (Full text)]

== See also ==
* [[Sick building syndrome]]
* [[Mold illness]]
* [[Gulf War Illness]]
* [[Development of new sensitivities]]
* [[Psychologization]]

== Learn more ==
*[https://www.mcs-aware.org/images/resources/Malcolm_Hooper_MCS_annotated_by_Gillian.pdf Multiple Chemical Sensitivity]<ref name="HooperCh" /> (book chapter) - Malcolm Hooper
*2010, [http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf Allergies and Multiple Chemical Sensitivity in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome]<ref name="Williams-allergies">{{Cite web|url=http://www.margaretwilliams.me/2010/allergies-and-mcs-in-mecfs.pdf|title=Allergies and Multiple Chemical Sensitivities in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome|last=Williams|first=Margaret|author-link=Margaret Williams|date=Nov 10, 2010|website=margaretwilliams.me|archive-url=|archive-date=|access-date=}}</ref> - Margaret Williams
*2019, [https://www.infoamica.it/wp-content/uploads/2019/07/CONSENSO-MCS-ENGLISH.pdf Italian Consensus on Multiple Chemical Sensitivity (English translation)]
*[https://www.msdmanuals.com/en-gb/home/special-subjects/idiopathic-environmental-intolerance/idiopathic-environmental-intolerance Idiopathic environmental intolerance] - MSD Manuals

== References ==
{{reflist}}

[[Category:Sensitivity signs and symptoms]]
[[Category:Neurological signs and symptoms]]
[[Category:Immune signs and symptoms]]
[[Category:Sensitivity signs and symptoms]]
[[Category:Diagnoses]]
[[Category:Environmental toxicology]]
[[Category:Potential comorbidities]]