Pallor

Pallor is undue paleness of the skin.

Presentation
Along with paleness of skin it is "observable also in certain mucous membranes, such as the conjunctiva and the lining of the mouth. Transient pallor may result from constriction of the blood vessels near the surface. Longer-term pallor may be due to anaemia or lack of exposure to sunlight. Permanent pallor may be caused by Albimism."

Symptom recognition
In the London criteria, facial pallor is mentioned under the criteria of periods of impaired circulation compatible with autonomic dysfunction. The Canadian Consensus Criteria recognizes extreme pallor as a cardiovascular symptom of ME/CFS.