Early-Life Ozone Exposure and Childhood Allergic Rhinitis: Critical Exposure Windows, Exposure-Response Relationships, and Protective Modifiers.

Childhood allergic rhinitis (AR) is associated with ozone (O3) exposure, yet the sensitive exposure window (SEW) remains unclear. This multicenter survey of 38,176 children aged 3-6 years across 7 Chinese cities (2019-2020) estimated satellite-based individual maximum daily 8 h average O3 exposure. The SEW and its exposure-response (E-R) relationship were assessed. Doctor-diagnosed AR prevalence was 11.9%. Average O3 exposure from prenatal to AR onset ranged from 67.5 to 76.7 μg/m3. The critical SEW was identified as infancy, specifically 30-38 weeks postnatal (7.5-9.5 months). Per interquartile range (IQR) (10.1 μg/m3) increase in O3, the adjusted odds ratio was 1.29 (95% CI: 1.22-1.36), independent of PM2.5. The E-R relationship was nonlinear, J-shaped, and threshold-free. The SEW effect was stronger in southern cities and mitigated by ≥6 months of exclusive breastfeeding. In conclusion, O3 significantly increases AR risk, with 7.5-9.5 months postnatal being a critical SEW, especially in exclusive breastfeeding <6 months and southern regions.