Multiple Chemical Sensitivity: Separating facts from fiction


One of the challenges to providing science-based medicine is managing debilitating symptoms in patients who lack a clear diagnosis. If a comprehensive workup on an ill patient reveals nothing conclusive, patients and their health care providers are equally puzzled and frustrated. A diagnosis is seen as giving legitimacy to symptoms, and can be the first step towards defining a science-based treatment plan. Vague or “medically unexplained” symptoms are among the most difficult therapeutic challenges. To patients, the science and profession of medicine has failed to “deliver” and the patient can be left feeling their condition lacks legitimacy. These patients are at the greatest risk for alternative medicine approaches, such as unorthodox diagnoses and treatments. In this world, the lack of objective evidence is no barrier to defining conditions and their treatments. One of the most problematic tactics used is the attribution of these symptoms to conditions known as fake diseases.

A “fake disease” doesn’t mean a patient’s symptoms aren’t real, or that they’re not suffering. Patients aren’t “faking” their symptoms. A “fake disease” means that the difficult work confirming the relationship between specific symptoms and an objective diagnosis is lacking. I’ve written about the fake disease called “adrenal fatigue” before. Steven Novella and Peter Lipson have examined a condition called Morgellons. Peter Lipson and Harriet Hall have discussed “chronic” Lyme disease at length. While different in how they are described, all fit the description of a fake disease. A real disease can be proven false or ruled out: There are objective ways to show someone does not actually have the disease. That’s not possible with fake diseases. They have a number of features in common:

  • A lack of scientific consensus on what the “disease” actually is.
  • A lack of scientific consensus on establishing who actually has the condition (and who does not).
  • Symptoms may be non-specific and common (e.g., headache), and there may be no objective differences from those without the condition.
  • A lack of objective evidence to establish a cause.
  • A reliance on unorthodox or unvalidated diagnostic techniques (e.g., food “intolerance” testing)
  • A reliance on unorthodox, unvalidated, or clinically useless treatments (e.g., colon flushing; dental amalgam removal)

The special pleading for fake disease

A recent series of articles in the medical journal Canadian Family Physician make the case for the existence of “multiple chemical sensitivity”, also known as “idiopathic environmental intolerance” (MCS/IEI), going so far as to call it a pandemic, using the terms “multimorbidity with sensitivities” and “idiopatic multimorbidity”. A close examination of the arguments and evidence presented in the “commentary” is nothing more than a special pleading for the scientific legitimacy of the condition, starting with the argument that we’re all toxic:

Just as accrued toxic compounds originating from cigarette exposure are a well established cause of various health conditions, myriad toxicants originating from many other day-to-day exposures are now bioaccumulating in people and causing a multitude of health conditions.21 To facilitate convenience, comfort, safety, and efficiency, there has been the manufacture and release of many thousands of untested synthetic chemicals over the past few decades. Extensive evidence published in various scientific and public health journals has recently verified that individuals from many population groups have experienced exposure to and bioaccumulation of numerous chemical toxicants from the air they breathe, from the food and drink they ingest, from vertical transmission, from dermal exposure, and from compounds injected or implanted into the body. Furthermore, the emerging field of nanotoxicology, a new discipline exploring the potential biochemical havoc resulting from exposure to some nanoparticles,22,23 has served to bring further attention to the expanding realm of potential toxicants. But just as the exposure problem from cigarettes, which was initially described by Delarue in the 1940s,24 was ignored for many years, the current exposure problem from innumerable domestic and occupational sources is also being ignored by many clinicians despite irrefutable and extensive evidence.

And yet, the author fails to actually present any irrefutable evidence at all. The rest of the column is a selection of cherry-picked citations that paint the picture of a civilization increasingly toxic, with some individuals manifesting an array of vague symptoms. It’s a paper more suited to Medical Hypotheses, rather than a supposedly peer-reviewed journal for primary care physicians:

A foray into the recesses of the scientific literature reveals discussion of a condition called sensitivity-related illness34 (SRI), with description of a credible causal mechanism39 to account for much of the emerging pandemic of multisystem health problems.40 This condition results when toxicant accrual within the human organism—typically from exposure to adverse chemicals—induces a state of immune dysregulation and hypersensitivity resulting in physiological disruption within various organ systems.4143 The pathogenesis relates to an intriguing phenomenon called toxicant-induced loss of tolerance,41,44 a finding that represents a considerable advance in medical science pertaining to the origins and mechanisms of disease.

There is a notable lack of any reference to a systematic review or even to any objective evidence at all. The literature search described (which includes the phrase “several books”) is laughably non-systematic, and the cherry-picking is evident. A comprehensive literature search would have identified that there is a lack of connection between the exposure to environmental agents and the onset of MCS/IEI symptoms. Furthermore, provocation studies that have evaluated those with MCS/IEI have failed to establish any relationship between active chemical exposure and placebo.

The second column from the same author, a “clinical review”, clearly demonstrates the unorthodox diagnostic approaches and treatments used in patients with MCS/IEI (and also called sensitivity-related illness, or SRI):

A 59-year-old rabbi experienced episodic headache, dizziness, and muscle discomfort beginning in adolescence. Into adulthood, these symptoms became more frequent and manifestations expanded to include episodic vision and hearing loss, inexplicable rashes, memory impairment, ataxia, profound agitation, and eventual blackouts. He also complained of intractable fatigue, insomnia, recurrent wheezing, musculoskeletal discomfort, and cognitive dysfunction.
The patient saw multiple physicians, but no physiologic cause for his multimorbidity was identified. Various diagnoses were given, but a subsequent psychiatric assessment conferred a diagnosis of “narcissistic, borderline personality disorder with extreme anxiety” to explain the totality of his presentation. As analgesic, asthma, and allergy medications provided minimal sustained benefit, psychotropic medication was employed but to no avail.

The treatment? Detoxify, of course:

The patient’s presentation was consistent with a diagnosis of SRI. Removal of inciting agents was meticulously carried out. In the early stages, the patient initially wore a filter mask designed to preclude particulate and volatile exposures both indoors and outdoors as required. The indoor air environment was initially addressed through a home inventory and associated high-efficiency particulate air filtration. Professional mold remediation was undertaken and follow-up mold testing was clear. Commercial scents, perfumes, and fresheners were eliminated. Common food triggers such as gluten, casein, refined fructose, nightshades, artificial sweeteners, and flavouring agents were temporarily eliminated from the diet.22
With these measures, the patient’s symptoms began to abate steadily and attention was directed to remediating his nutritional biochemistry.49 An organic, traditional whole food diet to minimize further toxicant and pesticide or herbicide exposure was implemented, along with directed supplementation to target specific biochemical deficiencies. With ongoing improvement, elimination of his total toxicant burden was commenced.
Amalgam removal employing exposure precautions and safe replacement materials was systemically done by a dental professional.5052 A saline nasal rinse with sodium bicarbonate was used for 3 weeks to eliminate residual mold from the sinus area, and detoxification measures were used to facilitate removal of residual mycotoxin.53 General measures to facilitate toxicant elimination were undertaken, including exercise and regular transdermal depuration.25,54,55 High serum levels of trans fatty acid were addressed with dietary counseling.

Regular readers of SBM will recognize the treatment regimen as lacking a sound evidence base. So what are the facts of MCS, and what’s actually known about the treatments?

The facts of multiple chemical sensitivity/idiopathic environmental intolerance

MCS and IEI are used to describe a condition with the following general characteristics:

  • Those affected report “sensitivities” or “allergies” to multiple products in the environment.
  • There are recurrent, non-specific symptoms reported to low levels of exposure.
  • There is a lack of objective evidence or laboratory findings that define any specific illness.

Reactions can be quite debilitating to those that report symptoms of MCS – some even wear masks in public (like the one illustrated above). MCS has had many names including “allergic toxemia”, “cerebral allergy”, and “ecologic illness” but is now referred to as MCS, (and IEI), to reflect the fact that any actual sensitivity to any chemical has not been established. The most commonly reported sensitivities are to products like perfumes, scented products, pesticides, solvents, “off-gassing” of products like carpets and plastics. Other contributors include food additives, dental fillings, and sometimes even electromagnetic waves. Candida is sometimes included as a toxin that also causes sensitivities.

The idea of MCS/IEI is not implausible. People could conceivably react in a strongly negative way to small exposures to a chemical irritant. However, scientific investigations fail to show a consistent or repeatable pattern of effects. Reactions to noxious chemicals can vary but usually cause symptoms like headache, fatigue, confusion, depression, and muscle/joint pain. There is no specific set of symptoms that establishes MCS or can clearly distinguishes it from syndromes like fibromyalgia. There are no established laboratory tests that can diagnose MCS. No biochemical model has been shown to cause MCS. Chemical sensitivities have been ruled out owing to chemical challenges that cause symptoms only in the absence of proper blinding. Consequently, the chemicals commonly blamed for MCS have not been shown to actually cause the symptoms of the condition.

MCS is not recognized as a distinct clinical entity in any country (with the exception of Germany and Austria) given the lack of confirmed physical effects and the lack of clear diagnostic criteria. Consequently, a diagnosis is currently based completely on self-reported symptoms.

Despite the relationship between symptomatic findings and investigations, unorthodox treatments offered for MCS range from dietary interventions to supplements and detoxification/desensitization approaches – many of which are described in the paper above. There is no objective evidence that the detoxification strategies purported by advocates improve health or address the problem. Science-based treatments are limited. Given the high prevalence of psychiatric comorbidity found with MCS, a relationship has been postulated, and treatments for conditions like anxiety or depression, with counselling like cognitive behavioural therapy (CBT) and sometimes drug treatments may be offered.

Position statements and scientific reviews on MCS/IEI

Consensus statements and other documents from medical and government agencies are in no way definitive guides to the evidence. However, they can offer a general overview of the literature, often with discussion of contrary (or unorthodox) perspectives. The most recent comprehensive summary was published in 2010 by the Australian government’s Department of Health and Ageing, entitled “Multiple Chemical Sensitivity, Identifying key research needs” [PDF]. It noted:

  • Insufficient evidence exists in the literature for benefit from any medication, dietary supplements or other therapies despite support for some of the treatments by some clinicians at their interviews or in response to the questionnaire.
  • People with the symptoms associated with MCS run a variable course but for most, MCS is a chronic condition.
  • The basic management involves engaging with the patient and maintaining a long-term supportive relationship whilst encouraging self-management as with all chronic illness.
  • Self-management involves providing the patient with information about the nature of the problems being experienced and guidelines regarding symptom management.
  • Clinicians need to accept the patient’s issues as a debilitating and disabling illness irrespective of whether the clinician recognises or accepts the presence of a specific entity, in order to avoid the patient seeking unnecessary referrals and harmful or costly treatment of unproven benefit.

The appendix to the document contains a summary of the views of governments and professional medical organizations. They include the American Academy of Allergy, Asthma and Immunology (AAAAI) which noted (in 1999) an absence of scientific evidence for any particular mechanism for the aetiology and production of symptoms in MCS and the lack of any immunological or neurological abnormalities in MCS subjects. Causal connections between environmental chemicals, foods and/or drugs and MCS symptoms “continue to be speculative”.


MCS is a debilitating but subjective condition attributed to exposure to a variety of chemical, biologic and other agents. While it not a distinct medical condition, those that suffer from MCS are heavy consumers of health care, and may devote considerable personal resources to managing their condition. MCS patients suffer – not only from a lack of clearly effective treatments, but also by being prey to purveyors of pseudoscience and quackery. Unproven diagnostic testing is common, particularly among alternative health providers and even medical doctors, many of whom claim a specialty in “environmental medicine” or “clinical ecology”. These practitioners attribute patient symptoms to a disease that doesn’t exist. Despite the claims by proponents, there are no clear diagnostic criteria for MCS, owing to the lack of connection between exposure to chemical triggers and reported symptoms. There is no objective evidence to demonstrate that commonly used “detoxification” methods for MCS have any meaningful effects. Consequently, there is no credible scientific justification for these treatments. Recent papers published in Canadian Family Physician fail to properly present a science-based perspective on MCS, and, by uncritically profiling pseudoscientific and unproven treatments, do a disservice to patients that suffer from this condition.

Despite the evidence, claims of MCS can be firmly held. Given the lack of objective symptoms and diagnostic criteria, science-based treatment focuses on active collaboration with patients to acknowledge symptoms, rule out serious medical issues (including objective physical illness), improve self-management techniques, and address any other conditions. As science-based practitioners, the best we may be able to offer is to treat with compassion, give facts instead of false hope, and equip our patients to identify and avoid quackery and their purveyors.

Photo from flickr user flahertyb used under a CC licence.

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