Environmental illness

Multiple chemical sensitivity (MCS), Idiopathic environmental intolerance (IEI)

Environmental illness


Idiopathic environmental intolerance (IEI) or MCS is briefly discussed here, as chronic allergy-like gastrointestinal symptoms form part of the syndrome. An increasingly postulated common chronic condition often classified as a somatoform disorder, it is also attributed to exposure to low concentrations of chemicals, triggering a wide variety of irritant and toxic reactions in often many body organs. Suspected substances include smoke, pesticides, plastics, synthetic fabrics, scented products, petroleum products, solvents, volatile organic compounds, and often additionally pollen, mites, and pet fur and dander.

The underlying mechanisms are poorly understand, but recent research has focused amongst others on possible deficiencies in the body’s detoxification enzymes, in neurotransmitter reactions to organic compounds, as well as abnormal conditioning processes. IEI is currently a controversial diagnosis,

which is not recognized as an organic illness by most medical associations or professional medical groups due to the inability to reproduce the symptoms in double-blind testing and the unusual distribution and often very low concentrations of offending chemicals. However, a consensus statement by IEI researchers has defined the following syndrome criteria:

  • Multiple chemical sensitivity
  • Symptoms are reproducible with repeated (chemical) exposures.
  • The condition has persisted for a significant period of time.
  • Low levels of exposure (lower than previously or commonly tolerated) result in manifestations of the syndrome (i.e. increased sensitivity).
  • The symptoms improve or resolve completely when the triggering chemicals are removed.
  • Responses often occur to multiple chemically unrelated substances.
  • Symptoms involve multiple organ systems.

Frequency in population



Symptoms of IEI differ from patient to patient and have a very broad spectrum. Symptoms involve multiple organs: runny nose, burning or itchy eyes, headache, scratchy throat, earache, scalp pain, mental confusion or sleepiness, wheezing, breathlessness, palpitations of the heart, upset stomach, nausea, abdominal pain, diarrhea, abdominal cramping, bloating, vomiting, fatigue, lethargy, impaired memory, skin rashes, itching, increased sensitivity to light and noise, sleeping problems, joint and muscle pain. Overlap with other syndromes, such as chronic fatigue, fibromyalgia, functional gastrointestinal syndromes, is evident.

Testing and diagnosis

A wide range of tests is advocated, including immunological, enzymatic and nutritional, which require further validation and substantiation. See “Causes” above for proposed diagnostic criteria.


Due to the complexity and continuous evolution of knowledge regarding IEI, suspected cases should be referred to an experienced and reputable treatment center after exclusion of other disease.

It should be noted IEI is currently not an accepted disease and the evidence base for treatment regimens is poor.

This is “work in progress”.