4.2 What is secondhand smoke?

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4.1 Background

4.2 What is secondhand smoke?

4.3 What is in secondhand smoke?

4.4 Cardiovascular disease and secondhand smoke

4.5 Lung cancer and secondhand smoke

4.6 Cancers of other sites

4.7 Health effects of secondhand smoke for infants and children

4.8 Effects of secondhand smoke on the respiratory system in adults

4.9 Secondhand smoke and pregnancy

4.10 Secondhand smoke and increased risk of infectious disease

4.11 Secondhand smoke and diabetes

4.12 Population prevalence of exposure to secondhand smoke in the home

4.13 Estimates of morbidity and mortality attributable to secondhand smoke

4.14 Public attitudes to secondhand smoke

Acknowledgments

References

Unless otherwise noted, the following section is compiled from recent reviews published by the Californian Environmental Protection Agency (2005)19 and the Office of the US Surgeon General (2006).20

Burning tobacco produces a complex mixture which comprises several thousand substances in the form of gases and particulate matter. The precise content of tobacco smoke varies according to the temperature of combustion, tobacco content, additives introduced during manufacture, type of paper wrapper encasing the cigarette, and type of filter used (if any); but overall, sidestream smoke varies little with the type of cigarette smoked.

Secondhand smoke is the term commonly used to describe the ambient smoke that is a by-product of active smoking. It consists of smoke that has been exhaled by the smoker (exhaled mainstream smoke) and smoke drifting from the smouldering tip of the cigarette (sidestream smoke). Sidestream smoke comprises about 90% of the mix,22 since smokers generally take only several puffs from a cigarette which may burn for some minutes. Smaller amounts of smoke also reach the environment by diffusion through the cigarette paper, and from the mouthpiece of the cigarette. Because most tobacco is smoked in the form of cigarettes, cigarettes are the major source of secondhand smoke. Other forms of smoking tobacco, such as cigars, pipes, kreteks and bidis, also produce secondhand smoke.

Mainstream smoke and sidestream smoke are chemically similar, but mainstream smoke undergoes some changes due to the process of inhalation. The action of inhaling through the mouthpiece of a cigarette creates airflow, which makes the tobacco burn at a higher temperature. Some constituents of the smoke are absorbed or retained in the smoker's lung tissue before exhalation. Sidestream smoke, produced at the burning end of the cigarette between puffs, is usually formed at a lower temperature, leading to incomplete combustion. This results in a greater quantity of compounds being released into sidestream smoke than mainstream smoke, per cigarette.