Independent and joint effects of apparent temperature and ambient air pollution on endometriosis-related outpatient visits in Beijing, China: a time-series study

Background Endometriosis is a chronic gynecological disorder, and its symptom fluctuations and healthcare utilization may be influenced by environmental exposures. Although meteorological factors and air pollution have been associated with short-term health outcomes in a range of inflammation-related conditions, evidence on their nonlinear, lagged, and joint effects on endometriosis-related outpatient visits remains limited. In particular, the combined impact of apparent temperature and air pollution on endometriosis-related healthcare utilization has not been well characterized.

In this time-series study, endometriosis-related outpatient visit records from Peking University First Hospital between January 1, 2022 and December 31, 2024 were linked with concurrent meteorological and air pollution data. A quasi-Poisson generalized additive model combined with a distributed lag nonlinear model was used to assess the nonlinear exposure-response relationships and lagged effects of apparent temperature and air pollutants on daily outpatient visits. Potential interactions were evaluated using stratified exposure-response analyses and additive interaction measures. Stratified analyses were further conducted by age group and season, with adjustment for long-term trend, seasonality, day of the week, and public holidays.

A total of 39,015 endometriosis-related outpatient visits were included. Apparent temperature showed a nonlinear and delayed association with daily outpatient visits. Relative to the median apparent temperature (11.44℃), high apparent temperature (P90, 29.45℃) was associated with an increased cumulative relative risk over lag 0–14 days (RR = 1.126, 95% CI: 1.078–1.177). In the single-pollutant models, higher concentrations of PM2.5 and PM10 were associated with increased cumulative relative risks (PM2.5, lag 0–7: RR = 1.109, 95% CI: 1.044–1.177; PM10, lag 0–6: RR = 1.070, 95% CI: 1.014–1.128). A statistically significant positive additive interaction was observed between apparent temperature and ozone (interaction relative risk [IRR] = 1.114, 95% CI: 1.053–1.180).

Apparent temperature and air pollution were associated with short-term fluctuations in endometriosis-related outpatient visits, and a positive additive interaction was observed between high apparent temperature and ozone. These findings highlight the potential importance of compound environmental exposures in shaping endometriosis-related healthcare demand under climate change and urban air pollution. Graphical abstract Similar content being viewed by others Abbreviations - AT: - Apparent temperature - AP: - Attributable proportion - AIC: - Akaike information criterion - CI: - Confidence interval - CO: - Carbon monoxide - DLNM: - Distributed lag non-linear model - IRR: - Interaction relative risk - MRI: - Magnetic resonance imaging - NO2 : - Nitrogen dioxide - O3 : - Ozone - PM: - Particulate matter - PM2.5 : - Fine particulate matter with an aerodynamic diameter ≤ 2.5 μm - PM10 : - Inhalable particulate matter with an aerodynamic diameter ≤ 10 μm - Q25: - 25th percentile - Q75: - 75th percentile - P10: - 10th percentile - P90: - 90th percentile - RERI: - Relative excess risk due to interaction - RH: - Relative humidity - RR: - Relative risk - SO2 : - Sulfur dioxide

The authors thank the staff of Peking University First Hospital for their assistance with clinical data extraction and management. The authors also thank the relevant meteorological and environmental monitoring authorities for providing access to the environmental data used in this study. Funding This study was funded by the Natural Science Foundation of Beijing, China (grant number 7202207). Author information Authors and Affiliations Corresponding author Ethics declarations Ethics approval and consent to participate This study was reviewed and approved by the Medical Ethics Committee of Peking University First Hospital (approval no. 2022 Yan 510-004). Given the retrospective design and the use of anonymized historical clinical visit data, the requirement for individual informed consent was waived by the ethics committee. All procedures were conducted in accordance with the Declaration of Helsinki. Consent for publication Not applicable. Competing interests The authors declare no competing interests. Additional information Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Rights and permissions Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material. You do not have permission under this licence to share adapted material derived from this article or parts of it. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by-nc-nd/4.0/. About this article Cite this article Wang, X., Feng, C., Huang, Y. et al. Independent and joint effects of apparent temperature and ambient air pollution on endometriosis-related outpatient visits in Beijing, China: a time-series study. BMC Public Health (2026). https://doi.org/10.1186/s12889-026-29056-8 Received: Accepted: Published: DOI: https://doi.org/10.1186/s12889-026-29056-8