Passive smoking is the inhalation of environmental tobacco smoke (ETS). ETS is a combination of sidestream smoke, which comes directly from burning tobacco, and mainstream smoke, which is exhaled from the smoker. Tobacco smoke contains over 4,000 chemicals and more than 60 of these are known to cause cancer in humans (NSW Health and The Cancer Council Fact Sheet, SHPN (TH) 070207).
For further information on the harmful effects of passive smoking, refer to the Australian Government Department of Health fact sheet: The dangers of passive smoking (opens an external link; PDF, 50 Kb).