Air pollution is composed of a particulate phase and a gaseous phase. The particulate phase, consisting of dust and aerosols, is the vehicle of toxic pollutants, transporting them into the respiratory tract. The irritants (sulphur dioxide, nitrogen oxides, aldehydes, and hydrocarbons) are the most important pollutants as regards health; the mucous membranes of the eyes and the respiratory tract are mostly affected. Other substances penetrate into the organism where they can develop actions harmful to various organs (carbon monoxide), generate cancer (polyaromatic hydrocarbons) or attack enzymatic systems (lead). Epidemiologic studies have revealed that populations exposed to high degrees of air pollution show increased mortality, which is mainly due to illnesses of the respiratory tract. Atmospheric pollution can also cause sensations of unpleasantness due to irritations of the eyes and the respiratory tract, bad odours, and the impairment of visibility and sunlight.