Chemical Sensitivity: A 1999 Consensus
A nutshell MCS definition:-
 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 and  requiring that symptoms occur in multiple organ
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
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
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 syndrome.”
“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 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 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
Voorhees RE. Memorandum from New Mexico Deputy State Epidemiologist
to Joe Thompson, Special Counsel, Office of the Governor; 13 March
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; 182:367–74.
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;
Meggs WJ, Dunn KA, Bloch RM, et al. Prevalence and nature of allergy
and chemical sensitivity in a general population. Arch Environ Health
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;
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
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: <http://www.DND.ca/menu/press/Reports/Health/health_study_e_vol1_TOC.htm>]
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
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; 17:345–51.
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, 1998.
Donnay A. A Resource Manual for Screening and Evaluating Multiple
Chemical Sensitivity. Baltimore MD: MCS Referral and Resources,
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
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 www.heldref.org.
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of this statement.