"Thirdhand smoke" is residual tobacco smoke contamination that remains after the cigarette is extinguished. Children are uniquely susceptible to thirdhand smoke exposure owing to their time spent in the home, their proximity to surfaces coated with thirdhand smoke, and the hand-mouth behavior of small children.

Thirdhand smoke contains many of the same contaminants as secondhand smoke and forms additional secondary highly carcinogenic pollutants with reactions to common household gases. Exposure to thirdhand smoke has adverse health impacts.  After a household member quits smoking, the house should become tobacco-free.