BACKGROUND: Despite mounting evidence linking allergic rhinitis (AR) to air pollution, it remains unclear which major air pollutant(s) and critical window(s) of exposure play important roles in children's AR. OBJECTIVE: To examine the effects of intrauterine and early postnatal exposure to outdoor air pollution on children with doctor-diagnosed allergic rhinitis (DDAR). METHODS: A retrospective cohort study involving 8689 kindergarten children was conducted in Changsha, China, from 2019 to 2020. A questionnaire survey was conducted to collect information on the health status of children and th...