Multiple Chemical Sensitivity
Multiple chemical sensitivity (MCS) is a controversial condition marked by heightened sensitivity to low levels of chemical exposures. Patients report disabling symptoms of fatigue, cognitive impairments, respiratory inflammation, headaches, among other symptoms, in uncontrolled studies (Ziem and McTamney, 1997). Although described by physicians since the 1950s, major medical associations have questioned the very existence of MCS (American College of Physicians, 1989; AMA, 1992; AAAAI, 1999). However, a recent evaluation of the biomedical literature, commissioned at the behest of the United Kingdom Health and Safety Executive, found “suggestive” evidence that MCS exists. Still, there are no pathological or laboratory tests. There are no widely used case criteria (Sparks et al., 1994). Most frequently, patients report that their symptoms are triggered or exacerbated by air pollution, cigarette smoke, solvent fumes, or perfumes (Buchwald and Garrity, 1994). No treatments for MCS have been studied in controlled clinical trials. On the basis of case studies and anecdotal reports, current treatments include avoidance (of the chemical[s] associated with symptoms), cognitive behavioral therapy, environmental control, diet, and sauna therapy (to mobilize and excrete toxins).
The etiology of MCS is unknown, although several models are being studied. The UK review cited above identified neuronal sensitization of the mesolimbic pathway of the brain as the etiological model with the best empirical support (Graveling et al.,1999). Sensitization refers to the progressive amplification of a given response after repeated exposures to the same stimulus. A battery of environmental chemicals (e.g., formaldehyde), endogenous substances (e.g., interleukin-2, corticotropin-releasing hormone), drugs (e.g., ethanol), and stressors (physical and psychosocial) can initiate neurobehavioral sensitization in animals (Bell et al., 1998a).