Smoking-Relapse Trajectories and Risk of Incident Asthma: Evidence From the 10-Year Korea Health Panel Survey (2009–2018)

BACKGROUND: Smoking relapse is prevalent, yet its long-term association with incident asthma remains underexplored. Repeated quit-relapse cycles may exacerbate airway inflammation more acutely than steady-state smoking. We investigated the association between smoking-relapse trajectories and incident asthma risk using a nationally representative longitudinal dataset. METHODS: We analyzed 10-year data (2009-2018) from the Korea Health Panel Survey for 16,240 adults without baseline asthma. Participants were classified into five trajectories: non-smokers (NS), successful quitters without relapse (SQ-), successful quitters with relapse (SQ+), unsuccessful quitters with relapse (UQ+, chronic relapsers), and always smokers (AS). Cox proportional hazards models were used to estimate adjusted hazard ratios (aHRs) for incident asthma (ICD-10 J45-J46). RESULTS: During the 10-year follow-up, 159 incident asthma cases were identified. Compared to NS, chronic relapsers (UQ+) exhibited the highest risk (aHR 3.81; 95% CI 1.84-7.91), followed by SQ- (aHR 2.54; 95% CI 1.30-4.96) and AS (aHR 2.25; 1.08-4.71). While UQ + showed a higher point estimate than AS, the difference was not statistically significant. Other significant risk factors included age ≤65 years, Medical Aid enrollment, and higher comorbidity scores. CONCLUSIONS: Smoking-relapse trajectories, particularly chronic relapse, are associated with an elevated risk of incident asthma. These findings should be interpreted as hypothesis-generating and require confirmation in independent cohorts.