Passive smoking is a cause of additional episodes and increased severity of symptoms in asthmatic children. Asthmatic children are up to 2.5 times more likely to have their condition worsened by passive smoking. In the United States alone it is estimated that 200 000 to one million asthmatic children have their condition worsened by passive smoking.

Exposure to environmental tobacco smoke (ETS or “passive smoking”) is a risk factor for new cases of asthma in children who have not previously displayed symptoms.

The risk of lower respiratory tract diseases (such as croup, bronchitis and pneumonia) is estimated to be about 50-60% higher in children exposed to ETS during the first 1-2 years of life, compared with unexposed children. About 10-15% of lower respiratory tract disease in young children under 18 months of age is attributable to passive smoking.

In children, exposure to environmental tobacco smoke is causally associated with increased prevalence of fluid in the middle ear, symptoms of upper respiratory tract irritation, and a small but significant reduction in lung function.

Environmental tobacco smoke is a cause of lung cancer in lifelong non-smokers exposed to ETS. Epidemiological studies carried out in several countries suggest that the lung cancer risk is about 20-30% higher than for never smokers not exposed to ETS.