'Multiple chemical sensitivity', the relevance of toxic, neurobiological and psychic effect mechanisms

The review deals mainly with the key question of chemical causation of multiple chemical sensitivity (MCS). There are only few human studies with valid information on chemical exposure and in no study the chemical toxic causation hypothesis is supported. The animal model of olfactory-limbic/neural sensitization is of heuristic value to explain MCS phenomena and includes both chemical and non-chemical stressors. However, in animal studies seldom chemical substances and exposure levels were used which might be of relevance in the formation of MCS. The problem is demonstrated for toluene exposures in human and animal sensitization studies. In accordance with the sensitization hypotheses, human studies prove a generalized vulnerability to environmental stimuli in subjects with self-reported MCS. However, study designs do not allow to deduce whether the strong responsivity is a premorbid or comorbid phenomenon or is related to exposure. Alternative study approaches to evaluate dose-response relationships are proposed.