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Multiple Chemical Sensitivities

People with Multiple Chemical Sensitivity (MCS), also known as idiopathic environmental intolerances or IEI, have (sometimes severe) reactions to certain chemical, biological, or physical agents, including solvents, VOC’s (Volatile Organic Compounds), pesticides, perfumes, cleaning products, whiteboard markers, gasoline, diesel, smoke, mold, certain food additives, and other chemicals.

A 2000 study found that roughly 40% of patients with ME/CFS also met the criteria for multiple chemical sensitivities (MCS). There is also a strong relationship between Long-COVID and MCS, but the frequency of having both syndromes is not yet known.

The symptoms of MCS are wide-ranging and may include burning and stinging eyes, wheezing, breathlessness, nausea, extreme fatigue/lethargy,  headache/migraine/vertigo/diz-ziness, poor memory and concentration, runny nose (rhinitis), sore throat, cough, sinus problems, skin rashes and/or itching skin, sensitivity to light and noise, sleeping problems, digestive upset, and muscle and joint pain.

Some people with MCS cannot tolerate certain chemical food additives. However, because many of the symptoms of MCS are similar to Long-COVID and ME/CFS symptoms, people are often unaware they have MCS and may not attempt to discover the source of their symptoms. If you suspect you may have MCS:

  • Identify and eliminate any non-dietary MCS triggers

  • Try organic, if possible

  • Eat completely unprocessed foods when possible

  • Work with your healthcare care professionals to decide if an elimination diet (where you remove many foods at once and then slowly re-introduce foods; or you remove a smaller group of suspected foods to see if symptoms improve) might work for you.

  • Magnesium and folate deficiencies are common and taking supplements may help with MCS

Note that restrictive and elimination diets can be difficult to follow and can lead to malnutrition if not done carefully.


Dieticians and doctors are split on the value and safety of elimination diets for MCS

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