Multiple Chemical Sensitivities

Much media attention and professional controversy has focused on the approximately 6% of the population who have multiple chemical sensitivity (MCS) (Kreutzer et al., 1999), i.e., severe low-level chemical intolerance (CI), multisystem chronic symptomatology, extreme chemical avoidant behaviors and associated disability. Chemical intolerance involves negative symptoms such as headache, dizziness, difficulty concentrating and/or nausea in response to the odors of low levels of environmental chemicals that the majority of people tolerate with neutral or even positive hedonic effects (Bell et al., 1996a, 1995). The triggering chemicals include multiple substances such as pesticides, solvents, perfumes, new carpets, automotive exhaust and tobacco smoke. A large proportion of people with chemical sensitivities also report multiple intolerances to common foods. Rates of immunoglobulin-E-mediated allergies per se are not necessarily elevated in MCS, although some patients may have immunoglobulin-G-mediated adverse food reactions. Thus, despite popular references to "chemical allergies," evidence for immune system disturbances as the primary mediator of MCS has not been persuasive, beyond possibly secondary adverse effects of chronic psychological and physical stress on cellular and humoral immune function (Winder, 2002). Figure 1 illustrates the point that all MCS patients have CI, but only a subset of people with CI meet diagnostic criteria for MCS.