Studies show that about 60 of about 4000 substances in tobacco smoke are carcinogens in laboratory animals including tar, nicotine, formaldehyde, and benzene. In humans, 24 of 30 epidemiological...

Studies show that about 60 of about 4000 substances in tobacco smoke are carcinogens in laboratory animals including tar, nicotine, formaldehyde, and benzene. In humans, 24 of 30 epidemiological studies support the conclusion that non-smokers exposed to secondhand smoke have a greater lung cancer risk than do unexposed people. (Secondhand smoke is the side stream smoke emitted between puffs of a cigarette plus the smoke exhaled by the smoker.) (a) Do these results indicate to you that secondhand smoke is a cancer risk? Explain. (b) What circumstances might increase the risk of developing cancer as a result of exposure to secondhand smoke?