Association between perceived exposure to secondhand smoke and depression independent of biomarker-measured exposure

Perceived exposure to secondhand smoke has previously not been distinguished from actual exposure dose when considering the association with depression. This cross-sectional study evaluated whether perceived exposure to secondhand smoke was associated with depression after adjusting for biomarker-based exposure. Adult non-smokers and ex-smokers (N = 16,926) were sampled from the Korea National Health and Nutrition Examination Survey from 2014 to 2020 biennially. Perceived exposure was defined by self-reported indoor secondhand smoke exposure in workplaces, households, or public locations in the past 7 days. Urine cotinine was used as the biomarker-measured exposure to secondhand smoke. Depression was defined as scoring 10 or above on the Patient Health Questionnaire-9. Logistic regression evaluated the association between perceived exposure and depression while adjusting for biomarker-based exposure, demographics, socioeconomic status, and comorbidities. Perceived exposure to secondhand smoke was associated with depression (adjusted odds ratio [aOR]: 1.60, 95% confidence interval [CI]: 1.31–1.95). Perceived exposure in occupational (aOR: 1.62, 95% CI: 1.17–2.25), household (aOR: 1.56, 95% CI: 1.14–2.13), and public (aOR: 1.57, 95% CI: 1.28–1.93) settings showed similar strengths of association with depression. Perceived exposure in one location (aOR: 1.49, 95% CI: 1.20–1.85) to three locations (aOR: 3.06, 95% CI: 1.55–6.07) showed dose–response associations with depression. Perceived exposure to secondhand smoke was associated with depression independent of actual biological exposure. Creating comprehensive smokefree environments should be prioritized to protect the general population from depression, with additional measures to reduce sensory cues of secondhand smoke where complete bans are not yet feasible.