Homes and workplaces are polluted by sidestream smoke which irritates eyes and airways and impairs lung functions longer than outdoor summer smog, is more mutagenic than particulates in a city with dense traffic and will cause more cancers in the population than all emissions of diesel, polycyclic aromatic hydrocarbons (PAH), benzene, asbestos and heavy metals together which are measured at present outdoors in Austrian towns and industrial areas. Lethal effects of passive smoking by placenta have been proven for the fetus and also breathing of parent's tobacco smoke may threaten life of babies by interactions with viral infections. In about 50% of asthmatic children passive smoking aggravates symptoms and in 10% it is a major aggravating factor. Even in healthy children we found significant relations between passive smoking and lung function deficit. Even though these deficits are small at school age they could be early symptoms of chronic inflammatory changes in small airways and indicate risk for later COPD.