Background: Environmental tobacco smoke (ETS) exposes adolescents to various environmental toxins, potentially affecting their developmental health. However, limited research exists on the associations between ETS exposure and the bodily burdens of environmental chemicals on adolescents. This study aimed to investigate the relationship between ETS exposure and the concentration of various environmental chemicals in adolescents, utilizing urinary cotinine as an objective biomarker. Methods: Data from 828 adolescents aged 12–17 years participating in the Korean National Environmental Health Survey (KoNEHS) were analyzed. ETS exposure was assessed via self-reported questionnaires and confirmed by urinary cotinine measurements. Levels of 33 environmental chemicals, including heavy metals, polycyclic aromatic hydrocarbons (PAHs), phthalates, phenols, volatile organic compounds (VOCs), and per- and polyfluoroalkyl substances (PFASs), were measured. Statistical analyses were conducted after adjusting for covariates. Results: Adolescents exposed to ETS showed significantly higher urinary cotinine and mono-(2-ethyl-5-carboxypentyl) phthalate (MECPP) concentrations than non-exposed adolescents. Additionally, significant positive correlations were observed between urinary cotinine levels and metabolites of PAHs (NAP, OHFlu), phenols (BPA, BPS), phthalates (MMP), and VOCs (t,t-MA) after adjustments. However, ETS exposure was not significantly associated with heavy metal concentrations. Conclusions: This study described the association between ETS exposure and environmental chemicals. A trend has been identified between ETS exposure in adolescents and increased bodily concentrations of various environmental chemicals, including PAHs, phenols, phthalates, and VOCs. As adolescence is a critical developmental period of vulnerability to environmental toxins, reducing ETS exposure to protect adolescents’ health and prevent potential lifelong health effects should be emphasized. This study was based on a cross-sectional design, and some confounding factors and measurement limitations may exist. Therefore, caution is needed in interpreting causality, and further research is recommended to determine more precise causality and long-term health effects.

Smartphone overdependence among adolescents is rising, prompting concern about its link to alcohol and tobacco use. While adolescent substance use has been widely studied, the impact of excessive smartphone use remains unclear. This study examined the association between smartphone overdependence and alcohol and tobacco use among Korean adolescents. This cross-sectional study analyzed data from the 2020 and 2023 Korean Youth Risk Behavior Web-based Survey and included 107,606 adolescents (54,985 males, 52,621 females). Smartphone dependence was measured with the Adolescents' Smartphone Overdependence Scale categorizing participants as general, potential-risk, or high-risk users. Multivariable logistic regression analyses adjusted for demographic and socioeconomic factors, perceived health, stress, sleep duration, and academic performance. Compared with general users, potential-risk users had higher odds of alcohol consumption (Odds Ratio = 1.22; 95% Confidence Interval 1.19-1.26) and smoking (OR = 1.26; 95% CI 1.20-1.32). High-risk users showed even greater odds of alcohol use (OR = 1.65; 95% CI 1.53-1.77) and smoking (OR = 2.32; 95% CI 2.11-2.56). A dose-response relationship was observed, with greater dependence linked to earlier initiation and heavier use. These findings highlight a significant positive association and underscore the need for longitudinal research and targeted prevention strategies.