It has been known for over 40 years that active smoking is a cause of disease in the smoker. Conclusive evidence that the inhalation of other people's tobacco smoke, or passive smoking, can be harmful to health, has accumulated in the past 20 years. Evidence that passive smoking caused respiratory illness in young children emerged during the 1970s and studies demonstrating health effects in adult non-smokers began to be reported in the early 1980s.