Background: Multiple Chemical Sensitivity (MCS) Syndrome poses many faces and it is related to previous exposure to substances found in the environment, at well-tolerated concentration by the general population. There are a lot of sources of exposure and there is no typical clinical pattern, as well as several degrees of severity in the subjects affected by MCS Syndrome. For all these reasons, the MCS Syndrome becomes a complex disease with difficult diagnosis and management. The aim of this study is to review and to update the available scientific evidence on MCS Syndrome.

Methodology: A systematic revision of the available evidence has been made, and updated the available evidence. The following sources were used: Medline, Embase, PSYCINFO, Toxline, UpToDate, IBSST, CISDOC, The Cochrane Library and Centre for Reviews and Dissemination (CRD). Two reviewers independently made the selection of recovered articles, applying the inclusion and exclusion criteria for the final selection of studies. There were identified 613 studies of which 27 were selected for the 5 analyzed clinical areas: 1) Epidemiology, 2) Clinical manifestations and co-morbid clinical conditions, 3) Diagnosis of MCS syndrome, 4) Physical, Psychological and Social impact on the Quality of Life 5) Therapeutic and prevention approaches for MCS Syndrome.

Results: The estimation of MCS's prevalence can range between 0.02% and 0.04%, increasing to 19% in people with an added diagnosis of allergy. The most frequently affected systems in the MCS Syndrome are the digestive tract, the cardiovascular one and the skin. Also, the mental sphere is affected with certain frequency. The MCS's diagnosis can be difficult, due to the variety of symptoms the disease can show from the beginning and because of the wide range of different definitions about the same disease that can be made. The clinical suspicion after a correct anamnesis and physical exam and the use of the Quick Environmental Exposure and Sensitivity Inventory (QEESI), in Spanish version can help with the diagnosis. People affected by MCS Syndrome seems to decrease their quality of life in a significant way, even reaching self-isolation in an attempt to reduce the exposition to trigger substances or due to the serious physical deterioration in case of continuous expositions. The more effective therapeutic intervention consists on avoiding new re-exposure to the leading substances.

Conclusions: The MCS is frequently associated with a previous allergic subject. It can affect multiple systems simultaneously, most often the gastrointestinal and cardiovascular systems, the skin and the mental sphere. The non-specific symptoms and the lack of consensus about the definition of MCS deter an early diagnosis of the disease. There is a Spanish version of the QEESI of reference. It is believed that the adoption of measures to sensitize the general population about MCS, could influence the reduction of exposures to trigger substances and improve understanding of this disease and people who suffer it. Actually, the best preventive measure is to avoid exposure to the triggering substances