Background: Previous studies have suggested that exposure to green spaces may be protective against allergic rhinitis; however, little is known of the role of air pollution as an effect modifier of the association between greenness and allergic rhinitis.

Aim: We aimed to evaluate the role of exposure to air pollution as a mediator or modifier on the association between exposure to green spaces and development of allergic rhinitis up to 27 years of age.

Methods: A longitudinal study was performed including the 2568 participants from the Espoo Cohort Study. Residential Normalized Difference Vegetation Index (NDVI) and individual-level exposure to ambient air pollutants during pregnancy and the first 2 years after birth were assessed using a Geographic Information System. Associations between cumulative exposure to NDVI and allergic rhinitis were estimated using Cox proportional hazards regression models.

Results: In children exposed to high levels of primary air pollutants (PM10, PM2.5, SO2, and NO2), an increase in NDVI during early-life in summer decreased the risk of allergic rhinitis up to 12 and 27 years of age. However, in children exposed to low levels of air pollutants, an increase in NDVI values in early-life in spring increased the risk of allergic rhinitis up to 12 and 27 years of age.

Conclusions: Our results suggest that air pollution levels may modify the associations between green space and allergic rhinitis, so that the beneficial effects of green space are stronger at high levels of air pollution.