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I have never smoked, but I have been exposed to a great deal of secondhand smoke. When I was growing up, from the late 1950s to the early 1970s, tobacco smoke was everywhere. I'm afraid this puts me at risk for lung cancer. According to the medical literature, exposure to secondhand smoke is most dangerous during the first 25 years of life, and it may take decades for cancer to develop.
Approximately 10 percent of lung cancers develop in individuals who have never smoked. Some of these can be attributed to asbestos, radon, or industrial chemicals. Of course, most of us over the age of 40 have been exposed to secondhand smoke. There is no risk-free level, according to a recent review article. Based on the fact that the lungs grow from birth to adulthood, and lung volume continues to expand until age 25, the authors of Reference 2 hypothesized that young people are more susceptible to lung damage from smoke. They performed a case-control study of 2,932 subjects. The results indicate that all individuals exposed to secondhand smoke have a higher risk of lung cancer, and this is significantly higher for those exposed before age 25. Thus, even if we wipe out secondhand smoke today, it will take another generation to wipe out its effects.
Tobacco smoke has two parts: mainstream smoke, generated during puff drawing, and sidestream smoke, emitted between puffs. The active smoker inhales the mainstream smoke, absorbs some of the constituents, and exhales the rest. Both mainstream and sidestream smoke consist of the vapor phase, containing volatiles including benzene, vinyl chloride, and acrolein, and the particulate phase, also called tar, containing semi-volatiles and non-volatiles including alkaloids, aromatic amines, and polycyclic aromatic hydrocarbons. The compositions of mainstream and sidestream smoke are similar. However, since the sidestream smoke is produced at a lower burning temperature, it has higher concentrations of certain carcinogens including aromatic amines. Smoke condensates have been tested on mice, and the sidestream smoke is more potent in producing skin tumors.