Chemical sensitivity: the scientific literature.

This article provides an overview of the scientific literature in which chemically sensitive patients have been directly evaluated. For that purpose, consideration of various case definitions is offered along with summaries of subjects' demographic profiles, exposure characteristics, and symptom profiles across studies. Controlled investigations of chemically sensitive subjects without other organic illnesses are reviewed. To date, psychiatric, personality, cognitive/neurologic, immunologic, and olfactory studies have been conducted comparing subjects with primary chemical sensitivity to various control groups. Thus far, the most consistent finding is that chemically sensitive patients have a higher rate of psychiatric disorders across studies and relative to diverse comparison groups. However, since these studies are cross-sectional, causality cannot be implied. Demonstrating the role of low-level chemical exposure in a controlled environment has yet to be undertaken with this patient group and is crucial to the understanding of this phenomenon.