Secondhand smoke (also called environmental tobacco smoke) is the combination of smoke emitted by the burning end of a tobacco product and the smoke exhaled by the smoker. Exposure to secondhand smoke is also called involuntary smoking or passive smoking. 

People are exposed to secondhand smoke in homes, cars, workplaces as well as public places such as bars, restaurants and other recreational settings.

 Of the chemicals identified in secondhand smoke, more than 50 have been found to cause cancer. They include arsenic (a heavy metal toxin), benzene (a chemical found in gasoline), beryllium (a toxic metal) and  cadmium (a metal used in batteries).

Others are chromium (a metallic element), ethylene oxide (a chemical used to sterilize medical devices), nickel (a metallic element), polonium–210 (a chemical element that gives off radiation) and  vinyl chloride (a toxic substance used in the manufacture of plastics). 

 Secondhand smoke causes lung cancer in nonsmokers. About 3,000 lung cancer deaths occur each year among adult nonsmokers in the United States as a result of exposure to secondhand smoke. Living with a smoker increases a nonsmoker’s chances of developing lung cancer by 20 to 30 per cent.

 Secondhand smoke causes heart disease in adults and a sudden infant death syndrome (SIDS), ear infection and asthma attacks in children. 

Exposure to secondhand smoke irritates airways and has immediate harmful effects on a person’s heart and blood vessels. It may increase the risk of heart disease by an estimated 25 to 30 per cent. There may also be a link between exposure to secondhand smoke and the risk of stroke as well as hardening of the arteries.

There is no safe level of exposure to secondhand smoke. Studies have shown that even low levels of secondhand smoke exposure can be harmful. 

The only way to fully protect nonsmokers from secondhand smoke exposure is to completely eliminate smoking indoors. Separating smokers from nonsmokers, cleaning the air, and ventilating buildings cannot completely eliminate secondhand smoke exposure