Ambient formaldehyde combined with high temperature exposure and respiratory disease admissions among children: a time-series study across multiple cities

Introduction Ambient formaldehyde (HCHO) is globally distributed, posing significant exposure to vast populations, particularly vulnerable demographics such as children. Investigations into the correlation between ambient HCHO exposure and children’s respiratory ailments are deficient. Methods Ambient HCHO exposure was retrieved from the TROPOspheric Monitoring Instrument. A two-stage time-series analysis was conducted to examine the relationship between HCHO exposure and hospital admission of respiratory diseases among 198 704 children in Jiangsu Province, China, from 2019 to 2021. Additionally, 12 exposure patterns were defined to further discern potential synergistic effects of HCHO and high temperature combined exposure. Results After controlling for relevant covariates, our findings revealed HCHO exposure was associated with respiratory-related hospital admissions. Specifically, we identified a pronounced effect at lag 3 day, demonstrating a 1.14% increase (95% CI: 0.60%, 1.69%). Subgroup analyses further identified that warm season, 3–7 years old group and disadvantaged economic areas showed higher admission risk. Moreover, we found HCHO combined with high temperature exposure would trigger the elevated risk of hospital admission. Notably, in specific exposure scenarios, the cumulative relative risk reached up to 1.051 (95% CI: 1.025, 1.078), highlighting the synergistic effect of combined exposure on the respiratory health of children. Conclusions Ambient HCHO exposure increased hospital admission risks for respiratory diseases in children, and high temperature could trigger the elevated risk. To have an in-depth understanding of ambient HCHO health impact is critical for intervention strategies aimed at mitigating ambient HCHO pollution and regarding adverse impacts on children under a changing climate.