A new study, aimed at assessing the prevalence of multiple chemical sensitivity (MCS) and its co-occurrence with asthma and fragrance sensitivity, as well as effects from exposure to fragranced consumer products[i]. The main findings were: 12.8% report a medical diagnosis of MCS; 25.9% report that they have MCS; prevalence of diagnosed MCS has increased over 300% in the last 10 years; and prevalence of self-reported MCS has increased over 200%.
The existence of MCS is disputed. Also known as idiopathic environmental intolerances, MCS is a chronic disorder, wherein patients report vague, non-specific symptoms such as fatigue, headaches and nausea that they attribute to exposure to common chemicals. Products such as pesticides, new carpet, paint, renovation materials, diesel exhaust, cleaning materials, perfume, scented washing powder and air fresheners have been implicated. The prevailing scientific viewpoint is that, although some people are sensitive to small amounts of one or a few specific chemicals, there is no general hypersensitivity to chemicals[ii].
Although the presence of symptoms, which in some patients can be disabling, is not disputed, it is difficult, scientifically, to attribute symptoms to chemical agents. Studies have shown that patients tend to develop symptoms when they are exposed to an agent and they know that they are exposed, usually when the agent has a smell, but that when the substance does not smell or the smell is masked, the patients’ reactions are no different to a sham or placebo exposure[iii]. A fundamental difficulty in studies that aim to investigate whether those reporting MCS react differently to true to sham exposures is that many agents have a smell, and so the study cannot be blinded. It is suggested that some patients’ symptoms may be a psychosomatic response that is ‘learned’ and triggered by the memories of the smell, rather than by the chemical agents themselves. However, other publications argue that the psychological factors may be over-stated[iv].
The new paper notes that, ‘Individuals with MCS may not receive a diagnosis but nonetheless exhibit the condition of chemical sensitivity’, and ‘… a single internationally agreed-upon standard for prevalence studies is not yet established’, but it does not explicitly point out that the actual existence of MCS is questionable. Data for the study was collected through an online survey, in which respondents were asked questions such as, ‘Has a doctor or health care professional ever told you that you have multiple chemical sensitivities?’, and, ‘Compared to other people, do you consider yourself allergic or unusually sensitive to everyday chemicals like those in household cleaning products, paints, perfumes, detergents, insect spray and things like that?’. Participants were also asked whether they had ever been diagnosed with asthma, and whether they experienced health problems from fragranced products. The study did not use any objective methods of assessing whether participants have MCS; the participants were not, for example, exposed to any agents.
In addition to the findings reported above, the results also showed that 71.0% of those self-reporting MCS are asthmatic, and 86.2% of those reporting MCS also experience one or more health problems when exposed to fragrances.
The paper concludes by reporting that the prevalence of MCS has increased across the American population, and that the results of this study provide evidence that MCS is widespread and increasing. However, the quality of this evidence is poor, because whether or not each participant has MCS was not assessed objectively. It cannot be claimed from this paper that the proportion of people who have MCS is any particular amount – it can only be claimed that the proportion of people who believe that they have MCS is a certain percentage. The authors discuss MCS as if it is a widely-accepted diagnosis, which it is not. Furthermore, no mention is made in the paper of studies that found that people claiming to be sensitive to chemicals have shown no difference in reaction when exposed to the chemical versus a sham exposure. Though headlines such as ‘One in four Americans suffer when exposed to common chemicals’ have appeared[v], this study offers no evidence for the existence or prevalence of MCS, and provides information regarding the participants’ beliefs only.
[i] Steinemann, A. National Prevalence and Effects of Multiple Chemical Sensitivities. Journal of Occupational and Environmental Medicine 60, e152 (2018). https://journals.lww.com/joem/Fulltext/2018/03000/National_Prevalence_and_Effects_of_Multiple.17.aspx (Accessed 16 March 2018).
[ii] Multiple Chemical Sensitity. Prepared for the American Council on Science and Health. Date unknown but probably mid-1990s.
https://www.acsh.org/wp-content/uploads/2012/04/20040426_mcs.pdf (Accessed 16 March 2018).
[iii] Das-Munshi, J., Rubin, G. J. & Wessely, S. Multiple chemical sensitivities: A systematic review of provocation studies. J. Allergy Clin. Immunol. 118, 1257–1264 (2006). (Accessed 16 March 2018).
[iv] https://www.tandfonline.com/doi/abs/10.1080/13590840802443133 Goudsmit, E. & Howes, S. Is multiple chemical sensitivity a learned response? A critical evaluation of provocation studies. Journal of Nutritional & Environmental Medicine 17, 195–211 (2008). (Accessed 16 March 2018).
[v] One in four Americans suffer when exposed to common chemicals. SceinceDaily. 14 March 2018. https://www.sciencedaily.com/releases/2018/03/180314092312.htm (Accessed 16 March 2018).