Multiple Chemical Sensitivity


The increased prevalence of allergic reactions among the general population – including breathing difficulties, sneezing, congestion, and rashes – has been suggestively linked to individual adverse physical reactions to low levels of common environmental chemicals. In turn, this has led to the creation of the term “multiple chemical sensitivity (MCS)” as a formal descriptor of this condition. While MCS is the term most often used by the general population, most physicians refer to it as idiopathic environmental intolerance (Heimlich 2008). Other terms that have been used to describe MCS include 20th century disease, environmental illness, idiopathic environmental illness, total allergy syndrome, and chemical AIDS (OSHA 2012).

MCS is a much-debated and highly controversial topic, with researchers and advocates on both sides of the argument as to whether or not MCS can and should be classified as a true illness. A major hurdle that prevents accurate and definitive classification of MCS as a disease is the complexity of chemicals in the environment and their ill-defined interactions with the human body. In addition, there is no known cause for MCS, symptoms vary greatly between patients, and symptoms overlap with those present in a multitude of other illnesses. The fact that many MCS patients have a documented psychiatric history also lends support to theories that MCS has psychologic rather than physical origins. Finally, most treatments that have been investigated for MCS have not proven useful at relieving symptoms (Heimlich 2008). Overall, the vagueness of MCS casts doubts among researchers and physicians as to its legitimacy as a true condition or illness, and impedes research efforts to better understand and classify the condition.

Possible Causes of MCS

A variety of theories have been suggested by those researchers who support MCS in an effort to explain factors that might trigger its symptoms, including allergies, immune system dysfunction, neurobiological sensitization, and a number of psychological factors. Furthermore, it has also been suggested that exposure to high levels of chemicals during the childhood years may lead to the development of MCS in adults (Heimlich 2008). However, the lack of scientific evidence to support a relationship between any of these potential causal factors and the clinical symptoms that characterize MCS continues to cloud its understanding. Aaron and Buchwald (2001) conducted a comprehensive review of published evidence for the overlap of “unexplained clinical conditions”, a label they use to encompass chronic fatigue syndrome (CFS), MCS, fibromyalgia, irritable bowel syndrome, temporomandibular disorder, tension headache, interstitial cystitis, and post-concussion syndrome. In their findings, they suggest that there is a high probability that complex interactions between both genetic and environmental factors as the likely cause of many of these conditions.

Due to the ambiguous information surrounding the entity that is MCS, individuals who experience symptoms attributed to MCS should be evaluated by a physician who is well-versed in its symptoms. Unfortunately, many physicians remain mystified as to how best to evaluate individuals who attribute their symptoms to low-level chemical exposures. Therefore, the diagnosis of MCS is generally based on the patient’s own description of their symptoms and the temporal relationship to recent environmental exposures.

Symptoms, Diagnosis, and Treatment of MCS

There does not appear to be one single stimuli or predictor of reactivity that is common among all patients. A majority of MCS patients report severe sensitivity or allergic reactions to a number of pollutants, including solvents, smoke, diesel fuel, and even pet allergens such as dander and fur. The most common include (but are not limited to): gasoline fumes, formaldehyde, paint fumes, cleaning products, furniture polish, perfumes and other aromatics, sugar, aspirin, cigarette smoke, and tap water. Although most symptoms attributed to MCS are frequently present in a variety of other illnesses, the most common include the following: stinging eyes, runny nose, breathing difficulties such as breathlessness and wheezing, nausea, muscle and joint pain, extreme lethargy and fatigue, and impaired memory and concentration.

Despite the ambiguous symptoms commonly associated with MCS,  a number of diagnostic criteria have been derived to assist in identifying patients who truly have MCS. These include: 1) reproducible symptoms with repeated exposure to particular triggers; 2) chronic nature of symptoms; 3) symptoms are triggered by both low and high levels of exposure; 4) symptoms either improve or completely resolve once the trigger is removed; 5) patients often respond adversely to unrelated substances; and 6) symptoms affect more than one area of the body.

Possible treatments that have been suggested include improved nutrition, immune system enhancements, education, and mental health treatment (Heimlich 2008); however, in light of the substantial inter-individual variations in exposures and symptoms, most physicians and mental health providers believe that avoiding the trigger(s) is the only consistent and effective means of treating MCS. This can be achieved through improved education regarding possible triggers, and the use of informed decision-making when purchasing medicines, cleaners, and even food.

Fibromyalgia and MCS

Many symptoms frequently reported among fibromyalgia patients overlap with many of those associated with MCS, as well as with chronic fatigue syndrome (CFS). These include muscle pain and weakness, cognitive impairment, and fatigue. In addition, all three conditions tend to occur most often in women, and in a majority of cases, the underlying cause is not understood and effective treatments can be difficult to find. The overlapping presentation, symptomotology, and demographics of these conditions have led many doctors and researchers so suggest that fibromyalgia, MCS, and CFS may co-occur in the same individual, or may actually represent different manifestations of the same disease. Other researchers have suggested that MCS may represent a specific symptom of fibromyalgia (Slotkoff et al., 1997).

A 1997 study sought to determine the prevalence of MCS among fibromyalgia patients. The study used a questionnaire designed to determine the presence of MCS based on a number of immune system criteria. In addition, the questionnaire  assessed the presence of 48 fibromyalgia-related symptoms. Out of the 60 fibromyalgia patients enrolled in the study, 33 were determined to meet the criteria for MCS. Of those, 11 were shown to have a high degree of MCS based on certain more restrictive criteria (Slotkoff et al., 1997).

Another study performed in a sample of 128 Canadian patients with MCS, fibromyalgia, and/or CFS also found considerable overlap among both patient symptoms and diagnoses. Forty-one patients had a diagnosis of MCS, 26 had a diagnosis of CFS, and 11 had a diagnosis of fibromyalgia. Among those with multiple diagnoses, 27 patients had both CFS and fibromyalgia, eight had CFS and MCS, and four had MCS and fibromyalgia. In addition to the overlap, the researchers also found that patients’ functional impairment increased with the presence of multiple diagnoses (Lavergne et al., 2010), a finding that has also been reported by other researchers (Brown & Jason, 2007).

One additional study designed to assess the co-morbidity of MCS, CFS, and fibromyalgia found 32 cases of CFS, 90 cases of MCS, and 22 cases of fibromyalgia among 213 individuals studied. Of those with CFS, 13 also met the criteria for MCS, and five met the criteria for fibromyalgia. Among those with MCS, 13 met the criteria for CFS and eight met the criteria for fibromyalgia. Finally, among the 22 fibromyalgia patients, five met the criteria for CFS and eight met the criteria for MCS. These rates of comorbidity were lower than reported in other studies; however, the authors suggest differences in patient sampling methods between studies may account for the discrepancy (Jason et al., 2000).

A 1994 study evaluated demographic, clinical, and psychological factors among 90 patients with chronic fatigue syndrome (CFS), fibromyalgia, and multiple chemical sensitivity (30 patients in each group). The researchers found that patients in all three groups reported significant overlapping symptoms, including fatigue, headaches, arthralgia (joint pain and stiffness), myalgia (widespread muscle pain), weakness, and sleep disturbances. In addition, memory impairments, confusion, and depression were also common symptoms among individuals in all three groups. Of interest, the study found that 53% to 67% of patients with CFS and 47% to 67% of patients with fibromyalgia reported adverse effects following exposure to pollution, gasoline fumes, paint and solvent fumes, and perfumes; however, sensitivity to these substances was reported more frequently among those with MCS (Buchwald & Garrity, 1994).

In a written critique of the Buchwald & Garrity study described above, Ziem & Donnay (1995) point out a number of flaws in the definition of MCS that the authors used to assess patients’ chemical exposures. However, they do acknowledge the significance of the finding of a high prevalence of adverse effects following chemical exposures among the CFS and fibromyalgia patients. They point out that symptom exacerbation following chemical exposure is the hallmark symptom of MCS, and is not known to be associated with any other condition. Therefore, they suggest that MCS may actually be more prevalent in the general population that previously thought, and that those patients with CFS and fibromyalgia who have multiple chemical sensitivity may in fact be misdiagnosed. To further support their assertion, they point to the fact that a diagnosis of MCS can account for the primary symptoms of CFS and fibromyalgia, however the reverse is not possible (Ziem & Donnay, 1995).

Learn more about Fibromyalgia Symptoms Here.



1.        United States Department of Labor; Occupational Safety and Health Administration (OSHA). Multiple Chemical Sensitivities.; Accessed April 5, 2012.

2.        Heimlich JE. Multiple chemical sensitivity. Community Development Fact Sheet CDFS-192-08. Copyright 2008; The Ohio State University. Accessed April 5, 2012.

3.        Aaron LA, Buchwald D. A review of the evidence for overlap among unexplained clinical conditions. Ann Intern Med. 2001;134:868-881.

4.        Slotkoff AT, Radulovic DA, Clauw DJ. The relationship between fibromyalgia and the multiple chemical sensitivity syndrome. Scand J Rheumatol. 1997;26(5):364-367.

5.        Brown MM, Jason LA. Functioning in individuals with chronic fatigue syndrome: increased impairment with co-occurring multiple chemical sensitivity and fibromyalgia. Dynamic Med. 2007;6:6.

6.        Buchwald D, Garrity, D. Comparison of patients with chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivities. Arch Intern Med. 1994;154:2049-2053.

7.        Ziem G, Donnay A. Chronic fatigue, fibromyalgia, and chemical sensitivity: Overlapping disorders. Arch Int Med. 1995;155:1913.

8.        Lavergne MR, Cole DC, Kerr K, Marshall LM. Functional impairment in chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivity. Can Fam Physician. 2010;56:e57-e65.

9.        Jason LA, Taylor RR, Kennedy CL. Chronic fatigue syndrome, fibromyalgia, and multiple chemical sensitivities in a community-based sample of persons with chronic fatigue syndrome-like symptoms. Psychosom Med. 2000;62:655-663.

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