Multiple chemical sensitivity (MCS) or idiopathic environmental intolerances (IEI) is a chronic medical conditionand syndrome characterized by symptoms that the affected person attributes to low-level chemical exposures to commonly used chemicals. Commonly attributed substances include scented products, pesticides, plastics, synthetic fabrics, smoke, petroleum products, and paint fumes. Symptoms are subjective and vague. Symptoms are also non-specific, meaning that they are common symptoms, such as fatigue or headaches, that are present in hundreds of other illnesses. Commonly reported symptoms also include nausea, dizziness, and inflammation of skin, joints,gastrointestinal tract and airways.

Although the symptoms themselves are real, and can be disabling, causes of MCS are not still perfectly known, this is why it is considered an idiopathic illness, linked to organic and chemical causes. Infact the World Health Organizationinserts MCS in the code T78 - "These codes, however, are not exposure codes by nature. Instead they are codes to be used for poisonings and certain other consequences of external causes. Therefore they should be used only for coding of such conditions and not as exposure codes"[1]. In this passage is clear that, even if the causes of the desease are not well known, the illness is linked to poisonings and certain other consequences of external causes. And even if theAmerican Medical Association, cannot not recognize causes of MCS, it affirms “The current consensus is that in cases of claimed or suspected MCS, complaints should not be dismissed as psychogenic, and a thorough workup is essential. Primary care givers should determine that the individual does not have an underlying physiological problem and should consider the value of consultation with allergists and other specialists.” [2]. The German Federal Institute for Occupational Safety and Occupational Medicine has mentioned MCS at the Thesaurus “Safety and Health at Work”, alphabetical Part, Status May 2009, as: B02.19.00 - Work related Disease and Occupational Disease/Disease. Furthermore, the Department of Health of the Austrian Government recognizes MCS – Multiple Chemical Sensitivity as a physical disease with the official letter dated June 24, 2009 regarding “Chemical Sensitivity / MCS – Multiple Chemical Sensitivity (T78.4)”. The Environmental Risk Management Authority of New Zealand recognised MCS from June 2002. Although MCS has had these official recognitions there is still a current of studies that suspected MCS is a psychological disorder. In support of this alternative theory, there is a study aboutBlinded clinical trials that have shown some MCS patients react as often and as strongly to placebos as they do to chemical stimuli; in these patients the existence and severity of symptoms is related to perception that a chemical stimulus is present.[3][4] Depression, anxiety, somatoform disorder, and similar mental health conditions are commonly associated with reports of MCS.[5][6] Patients with MCS often show emotional instability during their reactions to small amounts of chemicals. This has been likened to the epileptogenic effects of kindling which is particularly effective in the limbic system of the brain. Yet no proof of this concept has come forward to date.

We started doing PET brain scans on some of our patients with MCS and found that the limbic, hypothalamic and brain stem areas are hypermetabolic (in terms of their radioactive glucose uptakes) and therefore hyperactive (almost as seen during focal seizure activity).

Since the limbic system contributes emotional reactions and interpretations to sensory input, and since patients with amygdaloid (the amygdala is part of the limbic system) seizures can develop panic and related attacks during an amygdaloid seizure, our data appear to explain the emotional instability during a reaction to chemicals.

The previously mentioned structures also serve memory and cognitive as well as neuroendocrine and autonomic nervous system functions, all of which can be deranged in a patient with MCS.

Patients with MCS can develop hyperactivity in deep structures of the brain and that this may explain their emotional instability which therefore develops on a physiological rather than psychological basis.

It should be mentioned at this time that patients who are impaired and/or disabled from chemical injury and resultant MCS often become depressed. This depression would obviously be a natural reaction to their impairment and/or disability and therefore be a secondary depression.

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