Background The introduction of ‘smoke-free laws’ has reduced the population’s exposure to second-hand smoke (SHS), although SHS is still an issue in homes and other public places. Children are vulnerable to its health effects, and their greatest exposure occurs at home.

Objectives To assess airborne nicotine concentration of the living room and children’s bedroom of homes with children under 13 years of age, and to analyse factors associated with these levels.

Methods We conducted a cross-sectional study in Barcelona in 2015–2016, selecting a convenience sample from families with at least one child under 13 years of age. The sample comprised 50 families with smokers and 50 without. We measured airborne nicotine concentrations in the living room and children’s bedroom, and, using a questionnaire administered to the parents, collected information about smoking habits at home.

Results Homes without smokers showed nicotine concentrations below the limit of detection (<0.02 µg/m³), while those with at least one smoker showed 0.16 µg/m³ in the living room and 0.12 µg/m³ in the bedroom. When smoking was allowed inside home, these values increased to 1.04 and 0.48 µg/m³, respectively. Moreover, nicotine concentrations in both rooms were strongly correlated (r=0.89), and higher nicotine levels were associated with the number of cigarettes smoked in the living room, smoking rules, the number of smokers living at home and tobacco smell.

Conclusions Homes with smokers present SHS in the living room and in the children’s bedroom. Therefore, programmes focused on reducing children’s SHS exposure are urgently needed.