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

TL;DR

This study shows that smoke-free laws in Scotland greatly reduced secondhand smoke exposure, but progress has stalled and inequality in smoke-free homes has increased.

Contribution

The study provides a 20-year longitudinal analysis of SHS exposure and household smoking rules in Scotland.

Findings

Salivary cotinine levels in non-smokers dropped 95.7% from 1998 to 2024.

The proportion of smoke-free households increased from 75.2% in 2012 to 90.2% in 2024.

Inequality in smoke-free homes doubled between 2012 and 2024, with deprived areas having ten times higher rates.

Abstract

Scotland introduced comprehensive smoke-free legislation covering most enclosed public spaces in 2006. Twenty years on, this study examines changes in markers of population level exposure to secondhand tobacco smoke (SHS).

A secondary analysis of Scottish Health Survey data between 1998 and 2024 to examine trends in population exposure to SHS and household rules about smoking indoors. The proportions of non-smoking adults who had measurable cotinine in their saliva were calculated for the period 1998–2024. The geometric mean (GM) concentrations of cotinine levels were calculated using Tobit regression. Data from 2012–2024 on self-reported smoking rules for the home were analyzed.

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 measurable cotinine in their saliva increased by six-fold between 1998 (12.5%) and 2024 (77.6%). Most of the change occurred in the immediate aftermath of smoke-free legislation, with both metrics of population exposure to SHS demonstrating little evidence of change between 2011 and 2024. The proportion of households that are smoke-free has increased from 75.2% in 2012 to 90.2% in 2024 but is now ten times more common in the most deprived areas compared to the least deprived.

Scotland has sustained large reductions in SHS exposure since smoke-free legislation was introduced twenty years ago in 2006. However, progress evident in the years between 2006 and 2011 has not been maintained: there are still nearly one-quarter of non-smoking adults having measurable exposure to SHS on any given day. Smoking in the home has also reduced, but the level of inequality of this measure has doubled between 2012 and 2024. Public health interventions should consider the remaining workplace and home settings where people experience exposure to SHS.

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