Ambient air pollutants and outpatient visits for conjunctivitis in Hefei, China: a time-series study of hospital-based data during 2014–2023

Background Ambient air pollutants can directly act on the conjunctiva, triggering or exacerbating conjunctivitis. Nevertheless, evidence regarding the effects of common air pollutants on conjunctiva remains limited. Methods We collected 73,043 outpatient records of conjunctivitis visits to hospitals in Hefei from 2014 to 2023. A time-series study was adopted to investigate the short-term associations between five common air pollutants [i.e., aerodynamic diameter ≤2.5 μm (PM₂.₅), particulate matter with an aerodynamic diameter ≤10 μm (PM₁₀), ozone (O₃), nitrogen dioxide (NO₂), and sulfur dioxide (SO₂) and the risk of outpatient visits for conjunctivitis]. Furthermore, we explored the potential effect modification by gender, age, season, and the COVID-19 pandemic. Results Exposures to all five ambient air pollutants were positively associated with elevated daily outpatient visit risks for conjunctivitis, with the strongest single-day effects generally observed on the concurrent day of exposure (lag 0), while cumulative analyses indicated pollutant-specific short-term lag patterns. The magnitude of associations varied across pollutants; SO₂ showed the largest lag-0 effect estimate, followed by NO₂. Stratified analyses further revealed that season, gender, age, and study period modified the pollutant-conjunctivitis associations to varying degrees. Conclusion This study found that short-term exposure to PM 2.5 , PM₁₀, O₃, NO₂, and SO₂ was associated with increased outpatient visits for conjunctivitis, with evident subgroup heterogeneity. These findings may have implications for clinical practice and public health in the prevention of eye diseases against air pollution.