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Idiopathic Environmental Intolerance

(Multiple Chemical Sensitivity; Environmental Illness)

By Donald W. Black, MD, Vice Chair for Education, Department of Psychiatry, University of Iowa, Roy J. and Lucille A. Carver College of Medicine

Idiopathic environmental intolerance seems to be triggered by exposure to low levels of several identifiable or unidentifiable substances commonly present in the environment.

  • Symptoms may include rapid heart rate, chest pain, sweating, shortness of breath, fatigue, flushing, and dizziness.

  • Tests may be done to rule out allergic disorders as causes of the symptoms.

  • Treatment may involve psychotherapy, avoidance of certain substances, or both.

Idiopathic environmental intolerance is usually defined as the development of multiple symptoms that are attributed to exposure to any number of identifiable or unidentifiable chemical substances (inhaled, touched, or ingested) in a person who has no detectable organ dysfunction or related physical abnormalities.

Idiopathic environmental intolerance is more common among women than men. In addition, 40% of people with chronic fatigue syndrome (also called systemic exertion intolerance disease) and 16% of people with fibromyalgia also have idiopathic environmental intolerance.

Some doctors consider idiopathic environmental intolerance to have a psychologic cause, probably a type of somatic symptom disorder or an anxiety disorder similar to agoraphobia (fear of going out in public) or a panic attack. Others believe the disorder may be a type of allergic reaction. Various changes in the immune system may occur (although rarely), supporting the idea of an allergic reaction in some people. However, there is no consistent pattern of such changes among people who have this syndrome, and the cause remains unknown.


Some people start having symptoms after a single exposure to high levels of various toxic substances. People may attribute their symptoms to exposure to these substances, but evidence is usually lacking.

Symptoms may include a rapid heart rate, chest pain, sweating, shortness of breath, fatigue, flushing, dizziness, nausea, choking, trembling, numbness, coughing, hoarseness, and difficulty concentrating.


The diagnosis of idiopathic environmental intolerance is suspected if the symptoms

  • Recur after repeated exposure to the chemical substance

  • Recur after exposure to levels much lower than those that have been tolerated previously or that are commonly tolerated by others

  • Subside when the person leaves the offending environment

  • Develop in response to a wide variety of unrelated chemical substances

If a person's symptoms suggest idiopathic environmental intolerance, doctors try to identify possible causes of the symptoms, including other disorders. For example, symptoms could be caused by building-related illnesses (such as sick building syndrome), allergic disorders, some autoimmune disorders, or psychologic disorders. Depending on the person's symptoms and the findings during the physical examination, additional tests or assessments may be helpful. For example, blood and skin prick tests may be done to diagnose allergic disorders, or, if depression or anxiety seems possible, evaluation by a psychiatrist may help.


  • Avoidance of suspected triggers

  • Sometimes psychotherapy

People may try avoiding the toxic substances thought to cause their symptoms. However, avoidance may be difficult because many of these substances are widespread. Also, the substances being avoided may not be the true cause of symptoms, so avoidance may be ineffective. People should avoid too much social isolation. Psychotherapy can sometimes be helpful. The aim of psychotherapy is not to convince people that the cause of idiopathic environmental intolerance is psychologic. The aim, rather, is to enable people to cope with their symptoms and improve their quality of life.

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