Pollen exposure and mild allergy: A multi-city study in China

Pollen exposure is a key trigger for allergic diseases, yet limited monitoring and mild symptoms hinder conventional surveillance from capturing its immediate impact. This study used social media data to explore real-time links between pollen exposure and allergy-related posts in 25 mainland Chinese cities from May 2022 to December 2023. Pollen levels were obtained from monitoring data, and daily allergy-related posts on Weibo were collected via a two-stage crawling method and classified with machine learning. City-specific effects were estimated using generalized linear models, and pooled via meta-regression. The average daily pollen concentration was 127.66 grains/10³ mm². Each 10 grains/10³ mm² increase in pollen was associated with a 0.3 % (RR: 1.003; 95 % CI: 1.002, 1.004) higher risk of allergies. The strongest associations were observed for upper respiratory tract symptoms (RR: 1.010; 95 % CI: 1.007, 1.014), followed by lower respiratory tract symptoms (RR: 1.004; 95 % CI: 0.999, 1.009) and dermatologic symptoms (RR: 1.001; 95 % CI: 1.000, 1.002). Effects declined over longer lag periods and were strongest in northern cities and during autumn peaks. By integrating social media and environmental data, this study provides timely evidence of pollen's short-term health impact on allergy, highlighting the need for region- and season-specific public health strategies.