Background On 11 January 2009, Taiwan expanded its smoke-free legislation to all indoor public places and workplaces. This study examined the impact of this policy on secondhand smoke (SHS) exposure in adult non-smokers, across gender and socioeconomic status groups (SES).

Methods An annual sample of about 13 000–14 000 non-smokers was drawn from cross-sectional nationwide data of Taiwan Adult Tobacco Behavior Surveys during 2005–2011. Logistic regressions were used to analyse the aggregate data to estimate the association between the 2009 smoke-free legislation and SHS exposures in homes and workplaces. Interaction terms were used to examine the impact of the 2009 smoke-free policy on reducing differences in SHS exposure across gender, education and income groups.

Results The 2009 policy reduced the odds of SHS exposure in homes in 2009 (OR=0.76, 95% CI 0.68 to 0.84) and in workplaces (year 2009: OR=0.49, 95% CI 0.39 to 0.62; year 2010: OR=0.79, 95% CI 0.66 to 0.95). The model with interaction terms showed that men were more likely than women to be exposed to workplace SHS (OR=2.02, 95% CI 1.80 to 2.27) but were less likely to be exposed to home SHS (OR=0.79, 95% CI 0.73 to 0.86). SHS exposure in homes was significantly related to lower socioeconomic status, but the 2009 smoke-free policy reduced the difference in SHS exposure across education levels.

Conclusions The 2009 smoke-free policy reduced the SHS exposure for non-smokers. However, this impact on home SHS did not persist after 2009, and the effect of protection was unequal across gender and SES groups. Thus, further enforcement of smoking restrictions would be needed to reduce the risk of SHS exposure and improve protection against SHS risk among parts of the population with lower socioeconomic status.