Environmental tobacco smoke is smoke that is inhaled involuntarily or passively by someone who is not smoking. Secondhand smoke is classified as a “known human carcinogen” (cancer-causing agent) by the US Environmental Protection Agency (EPA). Cigarette smoke is a toxic mixture of more than 4,000 known chemical compounds. There is no safe level of exposure.
Thirdhand smoke is residual nicotine and other chemicals left on indoor surfaces by tobacco smoke. People are exposed to these chemicals by touching contaminated surfaces or breathing in the off-gassing from these surfaces.