To determine if the belief that thirdhand smoke is harmful to children is associated with smoking parents’ attitudes, home or car smoking policies, and quitting behaviors.


Data from a national randomized controlled trial, Clinical Effort Against Secondhand Smoke Exposure, assessed thirdhand smoke beliefs of 1947 smoking parents in an exit survey after a pediatric office visit in 10 intervention and 10 control practices. Twelve-month follow-up data were collected from 1355 parents. Multivariable logistic regression determined whether belief that thirdhand smoke harms the health of children is independently associated with parental behaviors and attitudes 12 months later. A χ2 test assessed whether parents who disagreed that thirdhand smoke is harmful were more likely to make a quit attempt if they later believed that thirdhand smoke is harmful.


Belief at the exit survey that thirdhand smoke is harmful was independently associated with having a strictly enforced smoke-free home policy (adjusted odds ratio: 2.05; 95% CI: 1.37–3.05) and car policy (adjusted odds ratio: 1.69; 95% CI: 1.04–2.74) at the 12-month follow-up. A significantly higher percentage (71% vs 50%) of parents who did not hold the thirdhand smoke harm belief at baseline made at least 1 quit attempt if they agreed that thirdhand smoke is harmful at the 12-month follow-up (P = .02).


Thirdhand smoke harm belief was associated with a strictly enforced smoke-free home and car and attempts to quit smoking. Sensitizing parents to thirdhand smoke risk could facilitate beneficial tobacco control outcomes.

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