This article summarizes (1) epidemiologic and clinical data on the symptoms of maladies in association with low-level chemicals in the environment, i.e., environmental chemical intolerance (Cl), as it may relate to chronic fatigue syndrome (CFS) and fibromyalgia; and (2) the olfactory- limbic neural sensitization model for Cl, a neurobehavioral synthesis of basic and clinical research. Severe Cl is a characteristic of 20-47% of individuals with apparent CFS and/or fibromyalgia, all patients with multiple chemical sensitivity (MCS), and approximately 4-6% of the general population. In the general population, 15-30% report at least minor problems with Cl. The levels of chemicals reported to trigger Cl would normally be considered nontoxic or subtoxic. However, host factors-e.g., individual differences in susceptibility to neurohormonal sensitization (amplification) of endogenous responses-may contribute to generating a disabling intensity to the resultant multisystem dysfunctions in Cl. One site for this amplification may be the limbic system of the brain, which receives input from the olfactory pathways and sends efferents to the hypothalamus and the mesolimbic dopaminergic [reward] pathway. Chemical, biologic, and psychological stimuli can initiate and elicit sensitization. In turn, subsequent activation of the sensitized limbic and mesolimbic pathways can then facilitate dysregulation of behavioral, autonomic, endocrine, and immune system functions. Research to date has demonstrated the initiation of neurobehavioral sensitization by volatile organic compounds and pesticides in animals, as well as sensitizability of cardiovascular parameters, β-endorphin levels, resting EEG α-wave activity, and divided-attention task performance in persons with Cl. The ability of multiple types of widely divergent stimuli to initiate and elicit sensitization offers a new perspective on the search for mechanisms of illness in CFS and fibromyalgia with Cl.
ASJC Scopus subject areas