Parental Smoking and Urinary Cotinine Levels in Non-Smoking Korean Adolescents: The Korea National Health and Nutrition Examination Survey, 2014–2021

Background/Objectives: Adolescents can be exposed to tobacco smoke at home even when they do not smoke. We examined the association between parental smoking and urinary cotinine in Korean adolescents, focusing on non-smokers. Methods: We analyzed 1173 adolescents aged 12–18 years whose father and mother both participated in the Korea National Health and Nutrition Examination Survey, 2014–2021. Parental smoking was defined by current status and by each parent’s smoking amount. Multiple linear regression was fitted on log10-transformed urinary cotinine, adjusting for adolescents’ own smoking, and refitted among non-smokers. Results: Median urinary cotinine was 0.62 ng/mL in non-smoking and 836.50 ng/mL in smoking adolescents. Among non-smoking adolescents, geometric mean urinary cotinine was 1.28 times higher when one parent smoked (95% CI 1.04–1.57) and 2.69 times higher when both smoked (n = 34; 95% CI 1.46–4.97) than when neither smoked. It was also higher when the father was a moderate-to-heavy smoker (1.42 times, 95% CI 1.15–1.76), whereas the estimate for the mother was imprecise (1.51 times, 95% CI 0.94–2.43). Adolescent smoking prevalence did not differ by parental smoking. Conclusions: Parental smoking, particularly heavy smoking by the father, was associated with higher urinary cotinine in non-smoking adolescents, supporting voluntary smoke-free homes; estimates for two smoking parents and for maternal smoking are exploratory.