Environmental tobacco smoke is a complex mixture of many chemical substances. The term passive smoking is used when a person breathes in air contaminated by tobacco smoke. Active and passive smoking expose an individual to the same substances, but the relative concentrations of the various substances differ. Thus, under conditions where individuals are exposed to an amount of nicotine corresponding to their smoking 1/2 a cigarette, they will be exposed to an amount of nitrosodimethylamine corresponding to their smoking about five cigarettes. Exposure of children to environmental tobacco smoke is associated with increased risk of lower respiratory tract infections, middle ear infections and asthma. Accumulating evidence points to passive smoking as a risk factor for the sudden infant death syndrome. Long term exposure to environmental tobacco smoke increases risk of lung cancer and heart disease. It is estimated that in Norway, 50 non-smokers die of lung cancer and 300-500 of heart disease annually, as a result of long term exposure to environmental tobacco smoke.