Multiple Chemical Sensitivity: recognition and management. A document on the health effects of everyday chemical exposures and their implications


British Society For Allergy , Environmental and Nutritional Medicine, PO Box 7, Knighton, LD& 1WT, UK
J. Nutr. & Env. Med. 2000; 10: 39-84

We live in a chemical world and all human metabolism is chemical in nature. However, for purposes of this document the term chemical will be used to describe chemicals which do not contribute to normal metabolism – mainly man-made synthesised chemical compounds and chemical pollutants . These may be termed xenobiotic. Some compounds in this category appear to be non-toxic, some are very toxic, others cause toxicity only at higher exposures or only in compromised individuals. Toxic effects may be acute or chronic . In keeping with the terminology of toxicology, the term toxin will be used to refer to natural substances, toxicant to synthetic chemicals.

However, this document, the third in our series [1,2], is not primarily concerned with toxicology although there will be areas that overlap. Xenobiotic chemicals have been reported to cause adverse effects in a minority of individuals at doses much lower than the lowest sensitivity (MCS) [3-6], that are the main focus of this report. Independent scientists in the USA[7] and the UK[8] have concluded that although there is still much to learn, it can no longer be doubted that MCS is a genuine complaint. There are indications that MCS may be at least partly, allergic in mechanism although not IgE-mediated [9]; the symptoms provoked are similar to those seen in ‘hidden’ food allergy. The term chemical sensitivity is a term describing the acquisition of a state enhanced sensitivity in which symptoms are provoked by exposures to very low concentrations of chemicals that previously had no effect [4,10]. It does not pre-empt the decision about the mechanism.

Classical toxicology has been concerned with acute and chronic reactions to compounds (not usually examining interactions between chemicals and has sought to establish threshold doses for toxic effects for each chemical below which it has been assumed that the product is without danger to people. However, effects of a range of familiar chemicals on the brain at sub-toxic doses are beginning toto be detected which are obviously likely to cause a rethink [11]. Chronic or delayed effects of exposure are notoriously difficult to detect and attribute, even in experimental animals. This is even more difficult if only a sub-population is involved, or if the effect occurs only with exposures to multiple compounds. Humans are now subjected to a mixture of chemical substances that change , not only from person to person , but also from day to day and from year to year, some of which accumulates in the body. Some evidence suggests that responses to foreign substances entering the body may actually be more damaging than higher levels because they do not trigger the induction of appropriate detoxification enzymes [12]. The full ramifications of the effects of the multiple chemicals to which humans are exposed have not been established but the chronic effects on which this report focuses are in addition to the recognised risks from carcinogenicity and mutagenicity; chemical exposures may also increase susceptibility to other etiological agents, and in particular to the development of allergic disease.

This report will focus on the evidence that adverse reactions occur consistently in a minority of individuals at exposures below the traditionally recognised toxic threshold, and will consider the clinical features and management of such conditions. In some of these cases there is a history of a single toxic exposure but in others the increased susceptibility seems to follow long-term exposure or exposure to multiple chemicals which may all be present at doses below the toxic threshold. The report will examine the extent of the problem, and evidence for the hypothesis that chemical exposures have contributed to the marked increase in the prevalence of allergies and related diseases in the last 200 years, especially the last 50 years .

These are relatively new fields of medical interest. They are neither classical toxicology nor standard allergy, but should be of concern not only to epidemiologists but also to clinicians. In the past , the medical profession has found sporadic cases of MCS difficult to recognise and accept, but this is beginning to change since chemical sensitivity has been recognised in a minority of individuals when groups have been exposed, for instance in work-related exposure incidents [13,14] or in new or refurbished buildings (so called sick building syndrome). Such incidents have been reported in the USA, Canada, the UK and most other countries in Europe.

A major reason for the emphasis on chemical sensitivity in this report is that this important area of human responsiveness has lacked an academic discipline to represent; those concerned with occupational health tend to think only of exposures at work. Physicians who have developed the skills to detect environmental actions among their patients recognise these phenomena on an almost daily basis although, as yet, it has remained largely unacknowledged in the UK. This is likely to change as a result of the independent report commissioned by the UK Health and Safety Executive [8], and by the recent European Union (EU) document [15]. The only previous UK scientific report on this problem, from the campaigning group Friends of the Earth [16], is written solely from the viewpoint of toxicology.

Chemical sensitivity presents regulatory problems to governments and employers with regard to exposure and use, restriction of trade and the provision of safe alternatives. The topic has been considered in a number of symposia and workshops in the USA 17-21].

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