Sick Building Syndrome and multiple chemical sensitivity: patient-related risk factors

Sick Building Syndrome (SBS) and Multiple Chemical Sensitivity (MCS), together with other conditions such as fibromyalgia, chronic fatigue syndrome, and Gulf War syndrome, grouped under the more general definition of "idiopathic environmental intolerances" (IEI), are clinical entities for which there is currently no clear definition, because of the lack of proven pathogenic mechanisms, the wide array of symptoms, the absence of clear dose-dependent clinical symptoms by exposure to triggering factors, and the absence of clear-cut diagnostic criteria 1. The attention of the scientific debate on these environmental pathologies is justified by the fact that they now represent a socio-economic problem of great magnitude, because of possible serious disability that may arise for individuals who are affected, with consequent low quality-of-life scores and partial or complete working and social disability. Just think that several European countries have listed MCS under the ICD (International Classification of Diseases) -10 code of the World Health Organization (WHO); also Japan since 2009 gives special attention to indoor pollution, causing SBS, considered a point of attention also by Canada. MCS is defined as a disorder attributed to exposure to extremely low levels of a wide variety of environmental chemicals 2, generally tolerated, which is manifested by an excessive awareness and intolerance of the individual to the same chemicals. SBS is instead characterized by subjective responses to nonspecific conditions3, however associated with the use of a building, just called "sick", and due to causes resulting from the complex interaction of several factors, such as air pollutant concentrations, personal exposure level, and individual susceptibility. While MCS is manifested as a long-lasting chronic disease, the symptoms of SBS disappear once left the building where they occurred. Although these syndromes are usually treated as two different clinical entities, there is evidence in the literature suggesting the presence of features common to both (table 1). In particular, SBS is often defined as a more limited form of environmental intolerance that, after further repeated exposure to pathogens, may develop into a chronic illness with chemical sensitivity4-5. Other authors have shown rather a real overlap between the two syndromes, when referring to the classification based on the pathogenesis of the Sick House Syndrome (SHS, a concept of Japanese origin and derived from the SBS) type 1 and 2, indicating symptoms of chemical intoxication and symptoms developed possibly due to chemical exposure, respectively 6, unlike MSC type 3 and 4, respectively showing symptoms developed not because of chemical exposure but rather because of psychological or mental factors and symptoms developed due to allergies or other diseases. To better characterize the relationship between exposure to chemicals and the occurrence of these complex syndromes, research has followed two basic approaches to identify the main risk factors, using the results of epidemiological and experimental studies on the physiopathogenic mechanisms and starting from the assumptions that underlie these environmental intolerances there is a dysfunction (molecular or genetic) of the defense network against chemicals. Although not yet come to final results, is now commonly accepted that the interaction between environmental factors and individual factors (such as genetic characteristics and lifestyle habits) is essential for the onset of these environmental conditions. The aim of this paper is to summarize the currently available data in the literature on MCS and SBS with regard to factors related to the individual that appear to be associated with the development of chemical sensitivity, a characteristic common to these two environmental pathologies.