Olfaction and symptoms in the multiple chemical sensitivities syndrome

Whereas most idiosyncratic: environmental sensitivity complaints do not fit known diagnoses, the multiple chemical sensitivities syndrome (MCS) is an extreme presentation that has defined diagnostic criteria. MCS symptomatics claim that they acquired a sensitized state as the result of a chemical ex posure, usually to a solvent or pesticide, but not to a fragrance. Before t his exposure, they did not experience symptoms. Following sensitization, sy mptoms increasing in number and severity with time are attributed by the MC S symptomatic to various exposures that are innocuous to most individuals. Although phenomenological studies have provided no evidence that particular odors elicit MCS symptoms, low levels of fragrances and perfumes are frequ ently associated with the reporting of MCS symptoms. This evaluation examin es proposed mechanisms by which odorants and fragrances might cause either sensitization or elicitation of MCS symptoms, including altered odor sensit ivity, primary irritancy or irritancy-induced upper airway reactivity, neur ogenic switching of trigeminal irritancy signals, time-dependent sensitizat ion and limbic kindling, CNS toxicity, and various psychiatric conditions. In no case was there persuasive evidence that any olfactory mechanism invol ving fragrance underlies either induction of a sensitized state or the trig gering of MCS symptoms. Fragrances and other odorants could, however, be as sociated with symptoms as claimed by MCS symptomatics, because they are rec ognizable stimuli, but fragrance has not been demonstrated to be causal in the usual sense. (C) 1999 American Health Foundation and Academic Press.