Associations of PM2.5 and Its Oxidative Potential with Childhood Allergy-Related Symptoms: A Cross-Sectional Study in Guangdong Province, China

Evidence linking PM2.5 exposure to allergic symptoms remains limited and inconsistent, partly because most studies rely on mass-based metrics alone. We conducted a population-based study among 131,346 children aged 6–18 years in six cities of Guangdong, China, to compare associations of PM2.5 mass concentration, oxidative potential (OP), and chemical components (metals, carbonaceous components, and ions) with rhinitis, rhinoconjunctivitis, and eczema symptoms. OP was assessed using the dithiothreitol assay and expressed as volume-normalized (DTTv) and mass-normalized (DTTm) metrics. PM2.5 mass and OP were generally positively associated with the three allergy-related symptoms. OP, particularly DTTm, provided more consistent and robust evidence of associations across outcomes than PM2.5 mass, supported by lower AIC/BIC values and greater stability in two-pollutant models. Single-component and mixture analyses indicated that multiple PM2.5 constituents contributed to allergy-related symptoms, and OP may partly explain the associations of Co, OC, Cu, and Hg, with the largest estimated indirect proportion reaching 36.2% for OC and rhinoconjunctivitis symptoms through DTTm. These findings suggest that OP captures health-relevant characteristics beyond particle mass and may serve as a complementary exposure indicator for understanding childhood symptoms of allergic diseases.