Smoking has been a leading agent of DNA damage in humans, and it not only affects the person who smokes but also people in the immediate surroundings. Cigarette smoke has been shown to have tar-phenolic compounds that can cause breaks in the DNA. These compounds can be inhaled by second hand smoking.
Suggested Reading:
http://apha.confex.com/apha/130am/techprogram/paper_43608.htm
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