Developmental trajectories of smoking susceptibility among Korean adolescents: A five-year longitudinal study using latent class growth analysis.

BACKGROUND: Smoking susceptibility predicts subsequent tobacco use, yet most research has treated it as static, measured at a single time point. How susceptibility develops over adolescence and how distinct patterns relate to multi-product tobacco use remain unclear in East Asian contexts. METHODS: Five annual waves (2019-2023) of the nationally representative Korean Youth Health Behaviour Panel Survey (n = 5045) were analyzed, following adolescents from grade 6 (age 11-12) to grade 10 (age 15-16). Susceptibility was assessed with a four-point willingness-to-smoke measure. Latent class growth analysis was applied to the five repeated susceptibility measures to identify trajectory classes. Associations with wave 5 lifetime use of cigarettes, e-cigarettes, and heated tobacco products (HTPs) were examined using the Bolck-Croon-Hagenaars method. Multinomial logistic regression identified baseline predictors, including peer smoking, parental disapproval, household smoking, perceived harm, media exposure, gender, academic performance, and socioeconomic status. RESULTS: Three trajectory classes emerged: low-stable (88.4 %), increasing (5.6 %), and high-decreasing (6.0 %); entropy was 0.812. Both the increasing and high-decreasing classes showed significantly higher lifetime use of cigarettes, e-cigarettes, and HTPs than the low-stable class. Lower parental disapproval, lower perceived harm, greater media exposure, male gender, and lower academic performance distinguished these two trajectories from the low-stable trajectory. CONCLUSIONS: Smoking susceptibility follows heterogeneous developmental trajectories during adolescence, and a small but identifiable subgroup shows escalating susceptibility associated with elevated risk for multi-product tobacco use. Findings highlight parental attitudes, harm perceptions, and media exposure as modifiable targets for early prevention.