Long-term exposure to PM10 and O3 and risk of pediatric allergic conjunctivitis: a national cohort analysis

Allergic conjunctivitis (AC) is a common ocular condition that impacts children’s quality of life. While ozone (O₃) and particulate matter (PM 10 ) are known risk factors, their long-term effects on childhood AC remain unclear. We investigated the association between long-term childhood exposure to O₃ and PM 10 and the risk of developing allergic conjunctivitis. By investigating the National Health Insurance Service–National Sample Cohort, we focused on individuals aged 0–18 years at enrollment. From 2002 to 2019, we defined the onset of mild AC as the first hospital visit with a diagnostic code of H10.1. Severe AC was defined as either the addition of steroid and cyclosporine eye drop prescriptions to a case of mild AC, or as a primary diagnostic code of H16.25. We assigned annual average exposure of both PM 10 and O 3 to 226 inland districts in South Korea using a machine learning-based ensemble prediction model. We applied a Cox regression model with time-varying exposures and covariates. In this study, we identified 364,227 individuals aged 0–18 at enrollment, among whom 137,491 experienced mild AC and 83,815 experienced severe AC during the study period. For each 5-unit increase in annual PM 10 and O 3 concentrations, the hazard ratios (HR) for mild AC were 1.02 (95% Confidence Interval (CI) 1.01–1.02) and 1.12 (95% CI 1.10–1.13), and HR for severe AC were 1.04 (1.03–1.05) and 1.23 (1.21–1.25), respectively. Notably, a younger age of onset was associated with a higher HR for both mild and severe AC with increasing PM 10 . Participants residing in urban areas exhibited elevated HRs for PM 10 and O 3 exposures on both mild and severe AC. Long-term exposure to PM 10 and O₃ increases AC risk in children, highlighting the need for environmental interventions.