As previously said, none of the symptoms of SBS can be addressed to a specic organic cause. Indoor parameters of temperature, humidity, ventilation rate, CO2 levels, microbial contamination (molds, viruses, bacteria), presence of dust and chemical compounds are the most studied factors. High indoor temperature over 23 °C, especially in overcrowded places, dust and poor cleaning are associated with SBS symptoms. Regarding ventilation, some studies show a relation between ventilation rates less than 10L/s/person an increased symptoms. In fact, higher ventilation rates can help dilute pollutants of the ofce which are generated by occupants, machinery, or that come from the outsidethrough windows or ventila­tion systems. On the other hand, augmented ventilation can also increase exposure to pollutants generated by ventilation systems themselvesmaking the relationship between ventilation and SBS not of unique interpretation. Actually, patients show improvement of symptoms when given individual ventilation control regardless of rates, temperature, and dust presence. In fact, respect of the standard levels of air humidication have not been shown to reduce SBS symptomsbut it is still impor­tant to respect them to avoid water stagnation, bacterial growth and the need to add bioceds:some of them, like isothiazolinones, glutaraldehyde, chloramine, chlorhex­idine, and benzalkonium chloride, have a knownirritant or allergenic potential. The role of microbial contamination is not clear in SBS etiology while it is more acknowledged in the genesis of alveolitis, humidier fever, and asthma. Paper and presence of printers, cigarettes smoke, air conditioner, and prolonged use of com­puter are all factors related to increased prevalence of sick building syndrome [1]. Indoor CO2 levels are mainly inuenced by the number of people present and ven­tilation: ahigherdifference between indoor and outdoor CO2 levels is related to symptoms such as fatigue and dizziness. This may have a biological explanation: an increase in blood CO