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During the 1980s a curious clinical syndrome emerged in occupational and environmental health practice characterized by apparent intolerance to low levels of man-made chemicals and odors. Although still lacking a widely agreed upon definition or necessarily permanent designation,1 the disorder idiosyncratically occurs in individuals who have experienced a single or recurring episodes of a typical chemical intoxication or injury such as solvent or pesticide poisoning or reaction to poor indoor air quality. Subsequently, an expansive array of divergent environmental contaminants in air, food, or water may elicit a wide range of symptoms at doses far below those which typically produce toxic reactions. Although these symptoms are not associated with objective impairment of the organs to which they are referable, the complaints may be impressive and cause considerable dysfunction and disability for the sufferer.

Although such reactions to chemicals are doubtless not new, there is an unmistakable impression that multiple chemical sensitivities, or MCS as the syndrome is now most frequently called*, is occurring and presenting to medical attention far more commonly than in the past. Although no longitudinal data are available, it has become prevalent enough to have attracted its own group of specialists—clinical ecologists or environmental physicians—and substantial public controversy. Unfortunately, despite widespread debate over who should treat patients suffering with the disorder and who should pay for it, research has progressed only modestly in the last two decades. Neither the cause(s), pathogenesis, optimal treatment, nor strategies for prevention have been adequately elucidated.

This sorry state of affairs notwithstanding, MCS is clearly occurring and causing significant morbidity in the workforce and general populations. It is the goal of the sections which follow to describe what has been learned about the disorder in the hope of improving recognition and management in the face of uncertainty and stimulating further constructive scientific engagement of this timely problem.

Definition and Diagnosis

Although, as noted, there has yet to be general consensus on a single definition of MCS, certain features can be described which allow differentiation from other well-characterized entities.2 These include:

  1. Symptoms appear to begin after the occurrence of a more typical occupational or environmental disease such as an intoxication or chemical insult. This ‘initiating’ problem may be one episode such as a smoke inhalation, or repeated, as in solvent intoxication. Often the preceding events are mild and may blur almost imperceptibly into the syndrome which follows.

  2. Symptoms, often initially very similar to those of the initiating illness, begin to occur after reexposures to lower levels of the same or related compounds, in environments previously well tolerated, such as the home, stores, etc.

  3. Generalization of symptoms occurs such that multiple organ-system complaints are involved. Invariably these include symptoms referable to the central nervous system such as fatigue, confusion, headache, etc.

  4. Generalization of precipitants occurs such that low levels of chemically diverse agents become capable of ...

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