UMDNJ-Robert Wood Johnson Medical School, Environmental and Occupational Health Sciences Institute, Piscataway, New Jersey 08854, USA
Sensitivities to chemicals are characterized by symptoms in
multiple organ systems in response to low-level chemical exposures.
This paper reviews studies of controlled exposures to odorants
and to mixtures of volatile organic compounds. Sensitive subgroups
include subjects who met Cullen's 1987 criteria for multiple
chemical sensitivity (MCS), Gulf War veterans with chronic fatigue
syndrome and chemical sensitivity (CFS/CS), and subjects with
specific self-reported sensitivities to methyl terbutyl ether
(MTBE) in gasoline (MTBE-sensitive). All studies include comparison
of age- and sex-matched healthy controls. Studies of olfaction
did not support unusual sensitivity, defined as lower odor thresholds,
among MCS subjects; however, a dose-response pattern of symptoms
was observed in response to suprathreshold concentrations of
phenyl ethyl alcohol. In blinded, controlled exposures to clean
air, gasoline, gasoline/11% MTBE, and gasoline/15% MTBE, a threshold
effect was observed with MTBE-sensitive subjects reporting significantly
increased symptoms to gasoline/15% MTBE exposure. Autonomic
arousal (heart and respiration rate; end-tidal CO
2) in response
to odor of chemical mixtures may mediate symptoms for subjects
with generalized chemical sensitivities, but not for those whose
sensitivities are confined to specific chemicals. For example,
Gulf War veterans with CFS/CS experienced reduced end-tidal
CO
2 when exposed to diesel fumes, while exposure to MTBE did
not produce any psycho-physiologic changes in MTBE-sensitive
subjects. Controlled olfactory and exposure studies reveal that
significant responses can be observed in chemically sensitive
subjects even when de-adaptation has not occurred. However,
these studies suggest that symptoms are not necessarily accompanied
by changes in physiologic arousal. Subject characteristics play
a critical role in outcomes.
