Asthma prevalence and risk factors in early-onset atopic dermatitis using Korean National Health Insurance Service data.

Early-onset atopic dermatitis (AD) is a common pediatric allergic disease and a potential precursor of asthma. However, population-based evidence on long-term asthma risk following early AD is scarce. This study assessed age-specific asthma prevalence and risk factors in children diagnosed with AD before age 2 using Korean National Health Insurance Service data. In this retrospective cohort, children with AD diagnoses (ICD-10: L20) at least twice before age 2 between 2008 and 2017 were included. Asthma was defined by diagnosis (ICD-10: J45, J46) and concurrent prescription of asthma medication. Patients were followed until December 2022. Standardized prevalence ratios (SPRs) were calculated relative to the general population, and multivariate logistic regression identified risk factors. Of 1,647,199 children with early-onset AD, 1,161,172 were analyzed. Asthma prevalence peaked at age 3 (29.0%) and declined to 0.5% by age 15, remaining significantly higher than in the general population. Increased risk factors included male sex, preterm birth, diagnosis before 2010, persistent AD, food allergy, and early rhinovirus or RSV infection. Diagnosis after age 1 and higher socioeconomic status were linked to lower risk. Early-onset AD is strongly associated with later asthma, highlighting the need for early identification and targeted prevention.