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Idiopathic environmental intolerance (multiple chemical sensitivity)

Donald W Black, MD
Scott Temple, PhD
Section Editor
Joel Dimsdale, MD
Deputy Editor
David Solomon, MD


Idiopathic environmental intolerance (IEI), formerly called multiple chemical sensitivity, is a subjective illness marked by recurrent, nonspecific symptoms attributed to low levels of chemical, biologic, or physical agents. These symptoms occur in the absence of consistent objective diagnostic physical findings or laboratory tests that define an illness [1,2]. Many experiments and observational studies consistently identify psychopathology in patients with IEI, and implicate behavioral or psychiatric causes for this illness [3]. This indicates that the underlying illness in many cases of IEI is actually a psychiatric disorder, such as a somatoform, depressive, or anxiety disorder [4].

This topic provides an overview of IEI, including clinical management of this condition. Related topics are discussed separately. (See "Somatization: Epidemiology, pathogenesis, clinical features, medical evaluation, and diagnosis" and "Unipolar depression in adults: Assessment and diagnosis" and "Unipolar major depression in adults: Choosing initial treatment" and "Generalized anxiety disorder in adults: Epidemiology, pathogenesis, clinical manifestations, course, assessment, and diagnosis" and "Pharmacotherapy for panic disorder with or without agoraphobia in adults".)


Patients with idiopathic environmental intolerance (IEI) typically report sensitivity to multiple, chemically unrelated substances and becoming ill with heterogeneous, nonspecific symptoms when exposed to low concentrations of chemicals [5-7]. Patients attempt to minimize exposure by modifying their lives, sometimes in far reaching ways.

These "chemically sensitive" people are sometimes treated by "clinical ecologists" or "environmental clinicians" who believe the disorder is acquired, highly prevalent in the general population, and goes unrecognized by most other clinicians.

The most frequently used term for this condition is "multiple chemical sensitivity," but many other terms have also been used, including "environmental illness." The World Health Organization in 1996 proposed the term "idiopathic environmental intolerance" (IEI) be used instead, because it avoids unsubstantiated assumptions of etiology, and many people attribute symptoms to environmental agents other than chemicals, such as food or electromagnetic forces [8].

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Literature review current through: Nov 2017. | This topic last updated: Jul 20, 2017.
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