Multiple Chemical Sensitivity:
A 1999 Consensus
Archives of Environmental Health v.54, n.3
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)
Clearly, there is a significant need
for a standardized clinical definition of MCS and a comprehensive
clinical protocol that VA, DOD, and other physicians can use to evaluate
it. We recommend to our colleagues and the sponsors of the Atlanta
Conference—the Department of Health and Human Services’ Office of Public
Health and Science, the Centers for Disease Control and Prevention, the
National Institutes of Health, and the Agency for Toxic Substances and
Disease Registry—that MCS be formally defined for clinical purposes by
the top 5 “consensus criteria” identified in a 1989 survey of 89
clinicians and researchers who had extensive experience in MCS but who
also held widely divergent views about its etiology.(14) Included were
36 specialists in allergy, 23 in occupational medicine, 20 in “clinical
ecology,” and 10 in internal medicine and otolaryngology. We would add
only that symptoms associated with chemical exposures must involve
multiple organ systems, thus distinguishing MCS from specific
single-organ system disorders (e.g., asthma, migraine) that also may
meet the first 5 criteria.
Consensus Criteria for MCS
The following consensus criteria
for the diagnosis of MCS were gleaned from the study by Nethercott et
al.(14) (funded in part by grants from US NIOSH and US NIEHS):
- “The symptoms are reproducible
with [repeated chemical] exposure.”
- “The condition is chronic.”
- “Low levels of exposure [lower
than previously or commonly tolerated] result in manifestations of
- “The symptoms improve or resolve
when the incitants are removed.”
- “Responses occur to multiple
chemically unrelated substances.”
- [Added in 1999]: Symptoms involve
multiple organ systems.
Given the only other explicit consensus
ever published on MCS—the 1994 statement of the American Lung
Association, American Medical Association, U.S. Environmental Protection
Agency, and U.S. Consumer Product Safety Commission, that “complaints
[of MCS] should not be dismissed as psychogenic, and a thorough workup
is essential” (ALA 1994)—we recommend that MCS be diagnosed whenever all
6 of the consensus criteria are met, along with any other disorders that
also may be present, such as asthma, allergy, migraine, chronic fatigue
syndrome (CFS), and fibromyalgia (FM). MCS should be excluded only if a
single other multi-organ disorder can account for both the entire
spectrum of signs and symptoms and their association with chemical
exposures, such as mastocytosis or porphyria, but not CFS or FM, which
are not so associated.
To assist physicians who are unfamiliar
with the evaluation of MCS, we recommend that clinical protocols include
validated questionnaires for screening and characterizing chemical
sensitivity,(15,16) a list of overlapping disorders to consider in the
differential diagnosis of MCS, and a list of signs and test
abnormalities associated with MCS in the peer-reviewed literature
(summarized by Ashford and Miller(17) and Donnay(18)). Although no
single test is yet considered diagnostic of MCS, those suggested by
signs, symptoms, or history may be helpful in treating and tracking the
The presentation of MCS may vary
greatly among cases and over time. Some individuals are totally disabled
by severe symptoms suffered on a daily basis, for example, whereas
others are disabled only minimally by mild symptoms suffered
occasionally. We, therefore, recommend that any clinical diagnosis of
MCS be characterized and followed over time using quantitative and/or
qualitative indices of life impact or disability (e.g.,
minimal, partial, total); symptom severity (e.g., mild, moderate,
severe); symptom frequency (e.g., daily, weekly, monthly); and
sensory involvement (identification of which sensory
pathways—olfactory, trigeminal, gustatory, auditory, visual and/or
touch, including perception of vibration, pain and heat or cold—show
altered (+/–) sensitivity and/or tolerance for normal levels of stimuli,
either chronically or in response to particular chemical exposures).
For research purposes that require
greater homogeneity, we encourage investigators to refine the consensus
criteria for MCS with whatever additional inclusion or exclusion
criteria they believe are needed to test their hypotheses. The indices
and domains that are used to characterize and select both cases and
controls in MCS research should be fully reported so that results from
different studies can be compared and their broader applicability
Given the significant overlap in clinic
populations of MCS with both CFS and FM, as well as the need to better
understand the relationships between these disorders,(19–21) we
recommend that all “solicitations” and “requests for applications”
issued by federal agencies for human research into any one of CFS, FM,
or MCS direct investigators to screen for all three (regardless of their
selection criteria, which need not be affected) and to report their
results in these terms. There is a precedent for this: the National
Institute of Arthritis and Musculoskeletal Disorders routinely requires
that in studies of fibromyalgia investigators must screen for and report
any overlap with temporo-mandibular joint disorder. CFS, FM, and MCS
research could all benefit from greater collaboration, and so we welcome
the Congressional initiative of Senator Tom Harkin to earmark $3 million
of the DOD’s 1999 Gulf War illnesses research budget for
multidisciplinary studies of CFS, FM, and MCS together (solicitation
074&&&-9902-0005 issued 2/12/99) to better understand both their
overlaps and differences. We recommend that such three-way studies be
solicited by all federal agencies funding CFS, FM or MCS research.
- Eisenberg J. Report to Congress on
Research on Multiple Chemical Exposures and Veterans with Gulf War
Illnesses. Washington DC: US Department of Health and Human
Services, Office of Public Health and Science. 15 January 1998.
- Kreutzer R, Neutra R, Lashuay N.
The prevalence of people reporting sensitivities to chemicals in a
population-based survey. Am J Epidemiol (in press).
- Voorhees RE. Memorandum from New
Mexico Deputy State Epidemiologist to Joe Thompson, Special Counsel,
Office of the Governor; 13 March 1998.
- Bell IR, Schwartz GE, Amend D, et
al. Psychological characteristics and subjective intolerance for
xenobiotic agents of normal young adults with trait shyness and
defensiveness. A Parkinsonian-like personality type? J Nerv Ment Dis
- Bell IR, Miller CS, Schwartz GE,
et al. Neuropsychiatric and somatic characteristics of young adults
with and without self-reported chemical odor intolerance and
chemical sensitivity. Arch Environ Health 1996; 51:9–21.
- Meggs WJ, Dunn KA, Bloch RM, et
al. Prevalence and nature of allergy and chemical sensitivity in a
general population. Arch Environ Health 1996; 51(4):275–82.
- Kang HK, Mahan CM, Lee KY, et al.
Prevalence of chronic fatigue syndrome among US Gulf War veterans.
Boston, MA: Fourth International AACFS Conference on CFIDS, 10
October 1998 (abstract and presentation).
- Bell IR., Warg-Damiani L, Baldwin
CM, et al. Self-reported chemical sensitivity and wartime chemical
exposures in Gulf War veterans with and without decreased global
health ratings. Mil Med 1998; 163:725–32.
- Fiedler N, Kipen H, Natelson B.
Civilian and veteran studies of multiple chemical sensitivity.
Boston, MA: 216th Annual Meeting of American Chemical Society,
Symposium on Multiple Chemical Sensitivity: Problems for Scientists
and Society, 26 August 1998 (abstract and presentation).
- Black DW, Doebbing BN, Voelker MD,
et al. Multiple Chemical Sensitivity Syndrome: Symptom Prevalence
and Risk Factors in a Military Population. Atlanta, GA: The Health
Impact of Chemical Exposures During the Gulf War–A Research Planning
Conference. 28 February 1999 (presentation, manuscript submitted).
- Fukuda K, Nisenbaum R, et al.
1998. Chronic multisymptom illness affecting Air Force veterans of
the Gulf War. JAMA 1998; 280:981–88.
- Canadian Department of National
Defense (CDND). Health Study of Canadian Forces Personnel Involved
in the 1991 Conflict in the Persian Gulf. Ottawa, Canada: Goss
Gilroy; 20 April 1998. [Online at:
- Unwin C, Blatchley N, Coker W, et
al. Health of UK servicemen who served in the Persian Gulf War.
Lancet 1999; 353:169–78.
- Nethercott JR, Davidoff LL, Curbow
B, et al. Multiple chemical sensitivities syndrome: toward a working
case definition. Arch Environ Health 1993; 48:19–26.
- Szarek MJ, Bell IR, Schwartz GE.
Validation of a brief screening measure of environmental chemical
sensitivity: the chemical odor intolerance index. J Environ Psychol
- Miller CS, Prihoda TJ. The
Environmental Exposure and Sensitivity Inventory (EESI): a
standardized approach for quantifying symptoms and intolerances for
research and clinical applications. Toxicol Ind Health (in press).
- Ashford NA, Miller CS. Chemical
Exposures: Low Levels and High Stakes (2nd ed). New York: John
- Donnay A. A Resource Manual for
Screening and Evaluating Multiple Chemical Sensitivity. Baltimore
MD: MCS Referral and Resources, 1999.
- Buchwald D, Garrity D. Comparison
of patients with chronic fatigue syndrome, fibromyalgia, and
multiple chemical sensitivities. Arch Int Med 1994; 154:2049–53.
- Slotkoff AT, Radulovic DA, Clauw
DJ. The relationship between fibromyalgia and the multiple chemical
sensitivity syndrome. Scand J Rheumatol 1997; 26:364–67.
- Donnay A, Ziem G. Prevalence and
overlap of chronic fatigue syndrome and fibromyalgia syndrome among
100 new patients with multiple chemical sensitivity syndrome. J
Chron Fatigue Syndrome 5(2):(in press).
Signatories to the
1999 Consensus on Multiple Chemical Sensitivity
Liliane Bartha, M.D.
William Baumzweiger, M.D.
David S. Buscher, M.D.
Thomas Callender, M.D., M.P.H.
Kristina A. Dahl, M.D.
Ann Davidoff, Ph.D.
Albert Donnay, M.H.S.
Stephen B. Edelson, M.D., F.A.A.F.P., F.A.A.E.M.
Barry D. Elson, M.D.
Erica Elliott, M.D.
Donna P. Flayhan, Ph.D.
Gunnar Heuser, M.D., Ph.D., F.A.C.P.
Penelope M. Keyl, M.Sc., Ph.D.
Kaye H. Kilburn, M.D.
Pamela Gibson, Ph.D.
Leonard A. Jason, Ph.D.
Jozef Krop, M.D.
Roger D. Mazlen, M.D.
Ruth G. McGill, M.D.
James McTamney, Ph.D.
William J. Meggs, M.D., Ph.D., F.A.C.E.P.
William Morton, M.D., Dr.P.H.
Meryl Nass, M.D.
L. Christine Oliver, M.D., M.P.H., F.A.C.P.M.
Dilkhush D. Panjwani, M.D., D.P.M., F.R.C.P.C.
Lawrence A. Plumlee, M.D.
Doris Rapp, M.D., F.A.A.A., F.A.A.P., F.A.A.E.M.
Myra B. Shayevitz, M.D., F.C.C.P., F.A.C.P.
Janette Sherman, M.D.
Raymond M. Singer, Ph.D., A.B.P.N.
Anne Solomon, Ph.D., M.A.
Aristo Vodjani, Ph.D.
Joyce M. Woods, Ph.D., R.N.
Grace Ziem, M.D., Dr.P.H., M.P.H.