Le syndrome d’intolérance aux odeurs chimiques (SIOC, MCS) est un ensemble de symptômes subjectifs variés, touchant plusieurs organes chez le même individu (brûlures buccales et pharyngées, dyspnée, asthénie, céphalées, difficulté de concentration…), qui se reproduisent à chaque exposition, surviennent pour des concentrations très faibles des substances incriminées, et qui n’entrent dans le cadre d’aucune affection organique connue. C’est l’une des facettes de l’intolérance environnementale idiopathique (IEI), l’autre étant l’intolérance aux champs électromagnétiques. Le point commun des produits responsables est leur odeur caractérisée : peintures, solvants, insecticides, détergents, eau de Javel, sprays, parfums, cosmétiques, plastique neuf… Tous les examens complémentaires sont normaux. Un auto-questionnaire standardisé (Quick Environmental Exposure and Sensitivity Inventory [QEESI^©]) permet de confirmer le diagnostic et de quantifier la gravité du syndrome. Aucun traitement n’a fait la preuve de son efficacité ; une psychothérapie peut dans certains cas améliorer la qualité de vie. Il est important pour le praticien consulté (souvent un allergologue ou un pneumologue) de savoir poser le diagnostic et d’évaluer le retentissement social et professionnel qui peut devenir majeur du fait de l’impossibilité d’utiliser des substances odorantes et de séjourner ou de travailler auprès de personnes parfumées ou dans des locaux neufs.

Multiple chemical sensitivity (MCS) is a chronic condition, which belongs to the group of medically unexplained syndromes. Patients (men as well as women) complain of many subjective symptoms such as nose and mouth irritation, sore throat, dyspnea, tiredness, dizziness, headache and concentration difficulties. Patient typically report at least four or five symptoms occurring when they are exposed to particular substances, at a very low concentration that usually does not cause symptoms or harm in normal individuals. The common feature of products that appear to be responsible (either occupational or domestic) is that they have a strong smell and include: solvent, paint, glue, tar, oil, pesticides, perfume, cosmetics and spray products. MCS is nowadays considered to be one aspect of idiopathic environmental intolerance (IEI) whose other main aspect is hypersensitivity to electromagnetic fields. If the diagnosis is suspected clinically it can be confirmed using the Quick Environmental Exposure and Sensitivity Inventory (QEESI^©) self-questionnaire. MCS is often misdiagnosed as asthma or an allergic conditions which means that patients are frequently referred to respiratory and allergy specialists. Misdiagnosis can lead to many futile medical investigations. Psychotherapy can improve quality of life in some cases. Preventive measures are often ineffective and do not stop the condition worsening: hypersensitivity can spread to common environmental odors so that a few people become severely disabled and limited in their workplace as well as in private life. In France, 435 cases were registered in the university hospital occupational disease departments network (RNV3P) during the period 2007–2010. It is therefore important that every clinician be able to recognize the condition and ensure that their patients could get compensation when unable to go on working.