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)
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
- “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 disorder.
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 assessed.
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
- 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 1998;
- 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
- 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 1997;
- 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 Wiley,
- 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.
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
The publisher grants permission for the free reprinting and distribution of