Air Pollution, Pollen, and Indoor Exposures in Allergic Conjunctivitis: A Systematic Review.

Environmental exposures are increasingly recognized as important drivers of ocular surface inflammation, yet their combined contribution to the onset, exacerbation, and clinical burden of allergic conjunctivitis (AC) has not been comprehensively synthesized. This systematic review evaluated the evidence linking air pollutants, aeroallergens, and indoor or occupational exposures with allergic conjunctivitis. The review was conducted according to PRISMA 2020 and AMSTAR-2 guidelines and registered in PROSPERO (CRD420251162399). PubMed, Web of Science, and Scopus were searched from inception to 18 September 2025. Two independent reviewers screened studies, extracted data, and assessed methodological quality using the MINORS tool. Owing to substantial heterogeneity, findings were synthesized narratively. Twenty-nine studies were included, encompassing more than three million outpatient visits. Consistent associations were observed between particulate matter, nitrogen oxides, sulfur dioxide, carbon monoxide, and ozone with increased AC incidence and symptom severity, with variations by age, sex, and season. Pollen and air pollutants frequently acted synergistically. Indoor exposures were associated with increased risk in children, while occupational settings demonstrated exposure-response relationships. Experimental studies identified mechanisms involving epithelial barrier disruption, NF-κB activation, and thymic stromal lymphopoietin signaling. Overall, environmental exposures substantially contribute to allergic conjunctivitis and may inform improved prevention and personalized clinical management.