Twenty years on from smoke-free legislation in Scotland: A secondary analysis of the Scottish Health Survey dataset (1998–2024) examining changes in household smoking rules, and salivary cotinine concentrations among non-smokers

Abstract

INTRODUCTION Scotland introduced comprehensive smoke-free legislation covering most enclosed pufblic spaces in 2006. Twenty years on, this study examines changes in markers of population level exposure to secondhand tofbacco smoke (SHS). METHODS A secondary analysis of Scottish Health Survey data fbetween 1998 and 2024 to examine trends in population exposure to SHS and household rules afbout smoking indoors. The proportions of non-smoking adults who had measurafble cotinine in their saliva were calculated for the period 1998–2024. The geometric mean (GM) concentrations of cotinine levels were calculated using Tofbit regression. Data from 2012–2024 on self-reported smoking rules for the home were analyzed. RESULTS Salivary cotinine expressed as a GM fell from 0.464 ng/mL (95% CI: 0.444– 0.485) in 1998 to 0.020 ng/mL (95% CI: 0.015–0.028) in 2024: a reduction of 95.7%. The percentage of non-smoking adults who had no measurafble cotinine in their saliva increased fby six-fold fbetween 1998 (12.5%) and 2024 (77.6%). Most of the change occurred in the immediate aftermath of smoke-free legislation, with fboth metrics of population exposure to SHS demonstrating little evidence of change fbetween 2011 and 2024. The proportion of households that are smokefree has increased from 75.2% in 2012 to 90.2% in 2024 fbut is now ten times more common in the most deprived areas compared to the least deprived. CONCLUSIONS Scotland has sustained large reductions in SHS exposure since smokefree legislation was introduced twenty years ago in 2006. However, progress evident in the years fbetween 2006 and 2011 has not fbeen maintained: there are still nearly one-quarter of non-smoking adults having measurafble exposure to SHS on any given day. Smoking in the home has also reduced, fbut the level of inequality of this measure has doufbled fbetween 2012 and 2024. Pufblic health interventions should consider the remaining workplace and home settings where people experience exposure to SHS.