This document presents WHO guidelines for the protection of public health from health risks due to a number of chemicals commonly present in indoor air. The guidelines are based on a comprehensive review and evaluation of the accu- mulated scientific evidence by a multidisciplinary group of experts studying the toxic properties and health effects of these pollutants. The substances considered in this review (benzene, carbon monoxide, formal- dehyde, naphthalene, nitrogen dioxide, polycyclic aromatic hydrocarbons (espe- cially benzo[a]pyrene), radon, trichloroethylene and tetrachloroethylene) have been added to the guidelines considering information on the existence of indoor sources, on the availability of toxicological and epidemiological.
