1999 MCS consensus statement
This article was published in the May/June 1999 issue of Archives of Environmental Health, Vol. 54, No. 3, pp. 147–149.
Heldref Publications, Helen Dwight Reid Educational Foundation http://www.heldref.org. The publisher grants permission for the free reprinting and distribution of this statement.
Multiple Chemical Sensitivity:
A 1999 Consensus
ABSTRACT. Consensus criteria for the definition of multiple chemical sensitivity (MCS) were first identified in a 1989 multidisciplinary survey of 89 clinicians and researchers with extensive experience in, but widely differing views of, MCS. A decade later, their top 5 consensus criteria (i.e., defining MCS as  a chronic condition  with symptoms that recur reproducibly  in response to low levels of exposure  to multiple unrelated chemicals and  improve or resolve when incitants are removed) are still unrefuted in published literature. Along with a 6th criterion that we now propose adding (i.e., requiring that symptoms occur in multiple organ systems), these criteria are all commonly encompassed by research definitions of MCS. Nonetheless, their standardized use in clinical settings is still lacking, long overdue, and greatly needed—especially in light of government studies in the United States, United Kingdom, and Canada that revealed 2–4 times as many cases of chemical sensitivity among Gulf War veterans than undeployed controls. In addition, state health department surveys of civilians in New Mexico and California showed that 2–6%, respectively, already had been diagnosed with MCS and that 16% of the civilians reported an “unusual sensitivity” to common everyday chemicals. Given this high prevalence, as well as the 1994 consensus of the American Lung Association, American Medical Association, U.S. Environmental Protection Agency, and the U.S. Consumer Product Safety Commission that “complaints [of MCS] should not be dismissed as psychogenic, and a thorough workup is essential,” we recommend that MCS be formally diagnosed—in addition to any other disorders that may be present—in all cases in which the 6 aforementioned consensus criteria are met and no single other organic disorder (e.g., mastocytosis) can account for all the signs and symptoms associated with chemical exposure. The millions of civilians and tens of thousands of Gulf War veterans who suffer from chemical sensitivity should not be kept waiting any longer for a standardized diagnosis while medical research continues to investigate the etiology of their signs and symptoms.
AS RESEARCHERS AND CLINICIANS with experience in the study, evaluation, diagnosis, and/or care of adults and children with chemical sensitivity disorders, we support the stated goal of the National Institutes of Health 1999 Atlanta Conference on the Health Impact of Chemical Exposures During the Gulf War “to fully characterize the nature of multiple chemical exposures within the Gulf War veteran population and to relate this characterization to what is known about Multiple Chemical Sensitivity (MCS) and related conditions and disorders within civilian populations.”(1) Based on research conducted by state and federal government agencies, we already know that MCS is one of the most commonly diagnosed chronic disorders in civilians and the most common—but still largely undiagnosed—disorder of any kind in Gulf War veterans of the United States.
In statewide telephone surveys of randomly selected adults, conducted by health departments in California in 1995 and 1996 and New Mexico in 1997, investigators found that 6% of adults in California(2) and 2% of adults in New Mexico(3) indicated that they had already been diagnosed with MCS or Environmental Illness, whereas 16% in both states said they were “unusually sensitive to everyday chemicals.” When randomly selected adults in other states were asked if they were “especially sensitive” (instead of “unusually” sensitive), one-third consistently maintained that they were.(4–6)
Among Gulf War era veterans, data from the largest random survey presented by the U.S. Department of Veterans’ Affairs (VA) in 1998 (based on questionnaires completed by 11 216 deployed to the Gulf and 9 761 nondeployed) show that 5% reported chemical sensitivity among the nondeployed personnel and 15% reported the same among the deployed.(7) Other VA researchers report much higher rates—but the same 3-fold difference—in a smaller random sample of VA hospital outpatients: 86% of ill veterans deployed to the Gulf complained of chemical sensitivity, compared with 30% of undeployed ill veterans.(8) In the only study in which MCS was specifically assessed among veterans selected randomly from the VA Registry, investigators found 36% of 1 004 met common research criteria for MCS.(9) Among randomly selected Department of Defense (DOD) personnel who remain on active duty, two larger studies by the Centers for Disease Control found slightly lower—but still significant—2.1- and 2.5-fold increases in the prevalence of self-reported chemical sensitivity among those deployed to the Gulf, compared with those who were not deployed. In the “Iowa” study, in which the prevalence rates for deployed and nondeployed individuals were 5.4% and 2.6%, respectively, investigators used a detailed questionnaire to assess “probable MCS.”(10) In the “Pennsylvania” study,(11) in which prevalence rates were 5% versus 2%, respectively, only one “yes/no” question was asked about chemical sensitivity. Canadian Gulf War veterans reported only approximately one-half the prevalence of MCS (2.4%), but nevertheless this was 4 times more than their controls.(12) Even in the United Kingdom where MCS is little known, Gulf War veterans report being diagnosed with MCS at 2.5 times the rate of military controls.(13)