About MCS

Invisible and mysterious, but very real

Multiple Chemical Sensitivity (MCS), sometimes referred to as Idiopathic Environmental Intolerance (IEI), is a poorly understood and controversial condition in which symptoms are experienced that are perceived to be related to chemical exposures.

MCS is a condition in which people experience unpleasant symptoms, seemingly as a result of exposure to such chemicals as solvents, paint, glue, tar, oil, pesticides, perfume, cosmetics and spray products.  These symptoms are brought on by minute exposures, at levels which would not bother most people.

MCS seems to be an aspect of Idiopathic Environmental Intolerance, a condition which also includes sensitivity to electromagnetic fields. MCS is considered to be a controversial diagnosis because a number of well-structured studies showed that the symptoms could be induced in study-participants using placebos such as clean air.

More recent research in neurology and brain chemistry suggest there are detectable differences in the physiology of people with MCS, although it is still not understood why or how these differences arise.

MCS affects both men and women.  It tends to be more common in adults than children but can impact people of any age.  Prevalence statistics are somewhat speculative due to the difficulty in confirming a diagnosis but tend to be in the range of about 3% of the total population.

What It Feels Like

People with MCS often have the following symptoms:

  • skin, nose and mouth irritation
  • sore throat
  • nausea, other gastrointestinal symptoms
  • dyspnea
  • tiredness
  • dizziness
  • headache
  • concentration difficulties
  • joint pain

The symptoms, which may be experienced as disabling, are usually recurrent and chronic.


Like CFS and fibromyalgia, MCS is a diagnosis of exclusion.  This means that other conditions should be ruled out before an MCS diagnosis is confirmed.  MCS may be misdiagnosed as asthma and/or allergies.  Once other causes are ruled out, the diagnosis is based on the following criteria:

  • The symptoms are reliably induced by repeated low levels of (chemical) exposure.
  • The symptoms have been persistent over time.
  • The symptoms subside or resolve when the exposure ends.
  • The symptoms are induced by a number of chemically unrelated substances.
  • The symptoms involve multiple organ systems such as the skin, eyes, nose, gastrointestinal tract, and joints.
  • Neurological symptoms such as hypersensitivity to odours, difficulty concentrating, and “spaciness” are present.

The Quick Environmental Exposure and Sensitivity Inventory (QEESI(©)) questionnaire is a useful tool for assessing suspected cases of MCS.

Treatment Options

One of the main forms of treatment is trigger-avoidance, however preventative measures are not always effective and will not stop the condition from worsening.  Psychotherapy can help those affected deal with the limitations imposed by their condition.

I have only treated one case of MCS, and in that instance, supplementation with vitamins and certain amino acids, along with a detoxification program, eventually yielded positive results.


Research on mouldy environments and hypersensitivity reactions to perfumes has established that it’s possible for immune responses to cause neurological symptoms with identifiable markers.  Ongoing research in environmental sensitivity will help to establish the pathophysiology that leads to MCS.

In the meantime, MCS remains a “mysterious malady” best treated by supporting the body’s efforts to heal, until such time as a definitive treatment is identified.