Multiple chemical sensitivity syndrome, an integrative approach to identifying the pathophysiological mechanisms

Multiple chemical sensitivity syndrome (MCS) is a chronic disorder characterized by multiple recurrent non-specific symptoms triggered or exacerbated by exposure to odours present in the environment at low concentrations—concentrations tolerated by most people.

People who are the most severely affected suffer from a chronic impairment that prevents them from functioning normally in their social and professional lives.

Various epidemiological studies have found different levels of prevalence of MCS in the general population, ranging from 0,5% to 3% for cases diagnosed by a doctor. This figure can be as high as 32% when selfdiagnosed cases are included.

In Canada, the number of annual medical consultations for individuals suffering from MCS greatly exceeds that of a comparable control population.

Against this backdrop, Québec’s ministry of health and social services, Ministère de la Santé et des Services sociaux (MSSS), entrusted Québec’s public health institute, Institut national de santé publique du Québec (INSPQ), with a mandate to formulate a scientific opinion on the current state of knowledge concerning the scientific and medical aspects of MCS.

An exhaustive analysis of more than 4 000 articles in the scientific literature led to the following findings:

  • Over the past two decades advances in neuroscience and the availability of new techniques for measuring biological parameters and performing functional brain imaging have shed light on the pathophysiological mechanisms underlying MCS. These developments confirm that the psychological, biological, and social aspects of MCS are inextricably linked.
  • Affected individuals perceive odours as a threat to their health. When they detect odours, they experience acute stress symptoms that manifest as ailments that they attribute to the chemical products associated with these odours.
  • This cascade of reactions triggers and perpetuates biological changes in the normal functioning of the individuals’ immune, endocrine, and nervous systems.
  • The nervous system is impacted mainly at the level of the limbic system structures involved in emotion, learning, and memory.
  • Collectively, the observed alterations explain the chronic and polysymptomatic experience reported by those suffering from MCS, which includes alterations in mood and cognitive functions, sleep disturbances, fatigue, loss of motivation, and the inability to feel pleasure. As a result, affected individuals are also more susceptible to the development of a variety of physical and psychological problems.
  • These alterations are not specific to MCS. They are also reported for chronic fatigue syndrome, posttraumatic stress disorder, electromagnetic hypersensitivity, fibromyalgia, depression, somatization disorder, phobias, and panic disorder.;. All of these disorders have in common is the presence of chronic anxiety.
  • Chronic anxiety helps explain all of the symptoms of SCM syndrome. The same alterations and dysfunctions are found and measured there.
  • Over the long term, the nearly unavoidable recurrence of these acute stress episodes in these individuals leads them to develop neuroinflammation, oxidative stress, and, inevitably, chronic anxiety.
  • Based on these new insights, the authors of this report rebut the hypothesis that there is a relationship between MCS and the toxicity of chemicals present at normal concentrations. Nonetheless, the chronic biological disturbances observed with this syndrome, the severity of the symptoms experienced, the social and professional repercussions, and the high prevalence of MCS in the population, qualify it as a real health issue.
  • Given that those suffering from MCS are, to varying degrees, genuinely ill and that their condition would justify appropriate medical and social support; the authors favor the establishment of centres of expertise specializing in MCS, as well as the continuation of the scientific monitoring of this syndrome.
  • This scientific advisory report is intended for physicians and healthcare professionals who will encounter MCS cases, for researchers in this field, and for MCS patients and their families.
Gaétan Carrier
Université de Montréal
Rollande Allard
M.D., médecin-conseil, Institut national de santé publique du Québec
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