Ways to quit smoking

Second hand smoke is the mixture of gases and particles from a burning cigarette (or other tobacco product) that end up in the surrounding air. The act of breathing in second hand smoke has been called “involuntary smoking” and “passive smoking” (in contrast to the “active smoking” of the cigarette smoker).

In the United States, public health advocates have argued for the use of the term “second hand smoke” as a matter of policy because it focuses attention on the nonsmoker who breathes in other people’s smoke. Researchers know much about second hand smoke’s composition and effects. More than half of the smoke (by weight) from a burning cigarette is second hand smoke. It is qualitatively similar to mainstream smoke: Both are produced by the combustion of tobacco and contain more than forty known or suspected human carcinogens, such as benzo(a)pyrene, 4-aminobiphenyl, and formaldehyde; irritants such as ammonia and nitrogen oxides; and compounds that affect cardiovascular function, such as smoke particles and 1,3-butadiene.

The exact concentrations of compounds in mainstream and second hand smoke differ quantitatively and change over time. Second hand smoke, which is produced while the cigarette sits idle, actually contains more harmful compounds than mainstream smoke, because it is generated at a lower, “dirtier” burning temperature. An additional reason exhaled smoke and sidestream smoke differ is because exhaled mainstream smoke has been filtered through the smoker’s lungs.

The health effects of active and passive smoking are not necessarily identical—although they are similar for cardiovascular effects—because it matters how the smoke is breathed, and specifically where the smoke lands in the lungs. The resources concluded that second hand smoke caused lung cancer in healthy adult nonsmokers and respiratory symptoms in children.