BackgroundWe investigated the association between paternal smoking, avoidance behaviors and maternal protective actions and smoke-free home rules with infant's saliva cotinine in Hong Kong.MethodsSix hundred and seventy-five non-smoking mothers (mean age 32.6 years) who attended the maternal-child health clinics with their newborns aged ≤18 months completed a questionnaire about paternal smoking and avoidance behaviors, maternal protective actions, smoke-free rules at home, and infant's second-hand smoke (SHS) exposure. Three hundred and eighty-nine infants provided saliva sample and its cotinine was tested.ResultsThe geometric mean of infant's saliva cotinine was 1.07 ng/ml (95% confidence interval (CI): 0.98, 1.16). Infants living in smoking families with SHS exposure had significantly higher cotinine level than in non-smoking families (adjusted β=0.25, 95% CI: 0.16, 0.33). Paternal smoking near infants (within 1.5 m) was associated with higher cotinine level (adjusted β=0.60, 95% CI: 0.22, 0.98), which was not reduced by avoidance behaviors (e.g., smoking in kitchen or balcony). Even fathers smoking ≥3 m away from infants was associated with higher cotinine level than non-smoking families (adjusted β=0. 09, 95% CI: 0.01, 0.16). Maternal protective actions and smoke-free home rules were not significantly associated with reduced cotinine level.ConclusionPaternal smoking avoidance, maternal protective actions, and smoke-free policy at home did not reduce infant's saliva cotinine.