Secondhand tobacco smoke and its effects on health

What is ‘secondhand smoking’? Secondhand smoke is tobacco smoke from other people’s cigarettes, pipes, and cigars. Breathing other people's smoke is called passive, involuntary or secondhand smoking. Also referred to as environmental tobacco smoke (ETS), secondhand smoke consists of mainstream smoke that has been inhaled and then exhaled by the smoker, and sidestream smoke from the burning tip of the cigarette.  Many potentially toxic gases are present in higher concentrations in sidestream smoke than in mainstream smoke and nearly 85% of the smoke in a room results from sidestream smoke. Secondhand smoke (SHS) is a major source of indoor air pollution. Its effects are far from trivial and pose a serious environmental health hazard. We know conclusively that ETS is a contaminant that contains over 4000 chemicals in the form of particles and gases - 60 of which are known carcinogens (cancer causing compounds). These are inhaled by and enter the bloodstream of non-smokers.

Since 1982 there has been a growing body of evidence, summarised below, which confirms that secondhand tobacco smoke is a serious health hazard. Research evidence has confirmed that there are strong links between secondhand tobacco smoke and lung cancer, resulting in hundreds of deaths each year.

Other studies show that individuals with chronic heart and lung diseases, and allergies such as asthma, are adversely affected by secondhand tobacco smoke.

Secondhand tobacco smoke can aggravate respiratory illnesses and contribute to more serious illnesses such as cancer. It can also injure the health of non-smoking partners and that of infants and unborn children.

Summary of research into the effects on health from secondhand tobacco smoke: A non-smoker has an estimated 24% greater risk of lung cancer if they live with a smoker. There is a direct relationship between the non-smoker’s risk of lung cancer and the years of exposure to secondhand tobacco smoke. Tobacco-specific carcinogens are found in the blood and urine of non-smokers who are exposed to secondhand tobacco smoke. All the available evidence confirms that exposure to secondhand tobacco smoke can cause lung cancer. 19 individual studies show that people who have never smoked have an estimated 30% greater risk of ischaemic heart disease if they live with a smoker. This equates to almost half of the risk attached to smoking 20 cigarettes a day even though the exposure is only 1% of that of a smoker. (Law, M.R., Morris, J.K., Wald, N.J., (1997). Environmental tobacco smoke exposure and ischaemic heart disease: an evaluation of the evidence. BMJ; 315: 973-980).

The Government's Scientific Committee on Tobacco and Health (SCOTH)  published extensive reviews of the scientific evidence in 1998 and again in 2004. The reports can be read here.