Dysgeusia

Dysgeusia is an altered sense of taste, which may involve a persistent unpleasant taste, ageusia is a total loss of sense of taste, and hypogeusia is a reduced ability to taste sweet, sour, bitter, salty or umami (delicious/savoury) tastes.

A change in sense of smell may occur alongside a change in sense of taste. https://books.google.com/books/about/The_Five_Senses_and_Beyond_The_Encyclope.html?id=4sFCDQAAQBAJ

Prevalence in ME/CFS

 * 2001, In a Belgian study, 38.0% of patients meeting the Fukuda criteria for chronic fatigue syndrome and 42.4% of patients meeting the Holmes criteria, in a cohort of 2073 CFS patients, reported changes in taste, hearing or smell.

Symptom recognition
An altered sense of taste is a potential symptom of Long COVID  in the World Health Organization's definition.

Possible causes
Common causes of altered sense of taste and/or smell include:
 * nervous system diseases, e.g., Parkinson's disease, Alzheimer's disease, or multiple sclerosis
 * colds, flu or flu-like illnesses, sinus problems and allergies
 * head injury
 * some drugs, e.g. zopiclone
 * some scientists have found altered or loss of smell and taste linked to COVID-19 illness in some patients

Learn more

 * Smell and taste disorders - John Hopkins University