Early-life exposure to outdoor temperature and the risk of childhood allergic diseases: A multicentre retrospective cohort study

Few research studies have shown the impact of temperature on childhood allergy, and less is known about the efficacy of mitigation methods such as the use of air-conditioning (AC). We aim to determine whether pre-schoolers’ allergic diseases and symptoms are associated with pregnant and postnatal exposure to ambient air temperature, and whether the use of AC mitigates this effect. A retrospective cohort study was conducted in nine Chinese cities between 2019 and 2023, involving 20,012 children aged 3–6 years. Demographics, socioeconomic status (SES), and indoor environmental factors were recorded. The exposure to twenty meteorological parameters, including temperature and seven air pollutants, was calculated. The relationship between temperature exposure with childhood allergic diseases and symptoms was studied using a two-level logistic regression analysis. We observed a significantly increased risk of childhood first-wave and second-wave allergic diseases associated with increased temperature exposure, especially daily minimum temperature (TEM-min), during pregnancy and postnatal period. The temperature increase during the first two trimesters and the third trimester were more important for asthma and food allergy, respectively. Sensitivity analysis revealed that children who did not have COVID-19 were more vulnerable to the allergy risk of temperature exposure. Temperature exposure was found to be significantly more associated with first-wave and second-wave allergic diseases in children who lived in non-air-conditioned homes. This change was more pronounced during prenatal exposure, particularly for daily maximum (TEM-max) exposure during the summer. Our findings indicate that temperature increases during early life has a significant impact on childhood allergies, which could be mitigated by AC use.