Importance E-cigarette use in public places may renormalise tobacco use.

Objective To measure associations between e-cigarette use in public places and social norms among youth.

Design Cross-sectional survey.

Setting School-based.

Participants 24 353 never tobacco users in US 6th–12th grades who completed the 2016–2017 National Youth Tobacco Surveys.

Exposure Individuals were classified as exposed in public places within the past 30 days to: (1) neither e-cigarette secondhand aerosol (SHA) nor combustible tobacco secondhand smoke (SHS); (2) SHA only; (3) SHS only; and (4) both SHA and SHS.

Outcomes Outcomes were overestimation of peer e-cigarette use (a measure of descriptive norms), harm perception and susceptibility. Data were analysed using descriptive statistics and logistic regression (p<0.05).

Results Overall prevalence of SHS and SHA exposure in public places was 46.6% and 18.3%, respectively. SHA exposure in public places was associated with increased odds of overestimating peer e-cigarette use (adjusted OR (AOR): 1.83; 95% CI 1.29 to 2.58) and decreased odds of perceiving e-cigarettes as harmful (AOR: 0.63; 95% CI 0.51 to 0.79), compared with those exposed to neither emission. SHA exposure in public places was also associated with increased susceptibility to using e-cigarettes (AOR: 2.26; 95% CI 1.82 to 2.81) and cigarettes (AOR: 1.51; 95% CI 1.20 to 1.90). E-cigarette harm perception was lower among students in jurisdictions with no comprehensive clean indoor air laws (AOR: 0.79; 95% CI 0.71 to 0.88) or cigarette-only laws (AOR: 0.88; 95% CI 0.78 to 0.99) than in those prohibiting both cigarette and e-cigarette use in public places.

Conclusions Prohibiting both e-cigarette and cigarette use in public places could benefit public health.