What is the multiple chemical sensitivity syndrome and what causes it?

Despite the causes and the development of this chronic disease are still unknown, its origin is related to the exposure to substances present in the environment


You have sent us a WhatsApp message (to 666 90 83 53) asking if it is true that multiple chemical sensitivity (MCS), a disease of difficult diagnosis that affects patients causing a great variety of symptoms which imply several organs and systems, has a psychological origin. The accumulated scientific evidence to date points to no. Despite the causes and the development of this chronic disease are still unknown, its origin is related to the exposure to substances present in the environment (such as solvents, hydrocarbons or heavy metals) at such low doses that they are considered incapable of causing adverse effects in the general population. Furthermore, there is no established treatment beyond controlling symptoms and avoiding exposure to triggers.

As of June 30 2021, the World Health Organisation (WHO) or the American Medical Association (AMA) still do not include the disease in their official lists, although several individual countries such as Germany, Switzerland, Austria and Japan do so. Spain recognised it as a disease in 2014, according to a report published by the Ministry of Health, which highlighted the unknown causes of the syndrome, although it linked it to exposure to chemicals present in the environment.

A chemical world

“We move in a chemical world”, Joaquim Fernández, Internal Medicine doctor and head of the Central Sensitisation Syndromes Unit at the Hospital Clínic de Barcelona, explains to Verificat. “It is a complex disease with many factors. Some of them depend upon the person, other upon gender and there is also a relation with a time-sustained exposure”, the expert develops, who concludes that “without exposure to chemical products, there is no disease”.

More than 144,000 artificial chemical products (created by humans) have been registered in Europe. They are found in the air (pesticides and combustion products), in food and water (fungicides and protective waxes), and are part of our daily lives (perfumes, plastics or adhesive tapes). The European Chemicals Agency (ECHA) is responsible for regulating the production and trading of chemicals at the European level to assure that they are safe for human health. 

It is difficult to estimate prevalence

It is known that some people are more sensitive to these products than the majority, and due to a continuous exposure to them at low doses develop symptoms related to the MCS. However, it is difficult to estimate prevalence. A report published in 2015 by the Ministry of Health calculated that the disease affects between 2 and 4 people per 10,000, but more recent studies raise this number up to 50 cases; others even put the prevalence at over 100 per 10,000 inhabitants.

The syndrome is more common in middle-aged women and causes a wide range of symptoms of different duration, intensity, and chronicity, ranging from headaches and muscle aches, cough and nausea, to asthma, anxiety and memory loss. The disease is chronic and "can become disabling," warns the doctor.

The MCS belongs to the central sensitivity syndromes group, including fibromyalgia and chronic fatigue syndrome. "This is a new field of pathologies related to the environmental burden and affecting very susceptible people," concludes the doctor.

Difficulty of diagnosis and treatment

The lack of knowledge of the biological causes originating the disease prevents the diagnosis from being made through analytic or exploratory tests, and doctors are forced to rely exclusively in clinical criteria, that is, in the set of symptoms by the patient and their history of chemical exposures: “We have case definition criteria for the disease, and impact questionnaires to determine the degree of impairment”, explains the expert.

The treatment is not unified as well: since the aetiology or the causes of the pathology are unknown, only symptoms can be controlled and exposure prevented, to the point of recommending, in some cases, isolation. As the Generalitat de Catalunya's Canal Salut website states, patients should "avoid re-exposure to products to which they have lost tolerance", for which it recommends "improving ventilation at home, avoiding humid environments, not exposing themselves to irritating environments (gases and smokes) and eating organic food". Even so, the website warns that the disease can "reduce the quality of life of those affected".

Theories about the psychological origin of the disease

Multiple chemical sensitivity has been the subject of controversy in the scientific community. In parallel to the studies that attribute a toxicological origin to it, many have linked the origin of the disease to psychological or psychosomatic causes (generating the symptoms from the psychological aspect). The absence of objective biological alterations has reinforced this hypothesis, which has not yet been completely discarded.

All in all, the scientific community seems to be leaning the balance towards the toxicological origin. The Spanish Society of Internal Medicine explains that "as the knowledge of MCS advances, the studies that direct research towards a toxic organic origin predominate and the number of studies that refer to a psychopathological cause decreases”.