Objective In recent decades, the prevalence of pollen-related allergic diseases have increased significantly worldwide, with particularly pronounced growth in urban environments. Rapid urbanization and global climate change have altered vegetation phenology and atmospheric conditions, resulting in earlier flowering periods, prolonged growing seasons, and increased seasonal pollen production in many cities. These changes are often species-specific and difficult to predict, which further complicates the management of allergenic pollen exposure. Urban green spaces, which concentrate diverse vegetation and support intensive human activities, have gradually become important sources of airborne allergenic pollen. While urban green spaces provide essential ecosystem services such as microclimate regulation, biodiversity conservation, and environmental improvement, they may simultaneously pose public health risks due to pollen exposure. Therefore, balancing the ecological benefits of urban green spaces with the mitigation of allergenic pollen risks has become a key issue in urban ecological management and public health protection. In this context, a systematic synthesis of existing research is necessary to better understand the species composition, spatial-temporal patterns, monitoring technologies, and risk assessment approaches related to allergenic pollen in urban green spaces. This study aims to comprehensively review global research progress on allergenic pollen, with particular attention to urban green spaces, and to identify future research directions that can support healthier and more sustainable urban green infrastructure.

Methods This study conducted a comprehensive bibliometric analysis and literature review of allergenic pollen research. The Web of Science Core Collection database served as the primary data source, and the search strategy (TS = pollen) AND (TS = allergy OR allergies OR allergen OR allergenicity OR allergic OR allergenic) was applied to retrieve relevant publications. A total of 17,252 records published between 2000 and 2024 were obtained. To analyze global research trends and knowledge structures, the bibliometric visualization software CiteSpace (version 6.3.R1) was employed to conduct keyword clustering, co-occurrence analysis, and burst detection. Keyword burst detection was used to identify emerging research fronts by detecting keywords that experienced rapid increases in frequency within specific periods. In addition, the China National Knowledge Infrastructure (CNKI) database was searched using Chinese keywords related to allergenic pollen, yielding 655 publications. The domestic research literature was further analyzed from multiple perspectives, including publication year, research themes, disciplinary distribution, and institutional participation. On this basis, the study synthesized existing findings from aerobiology, urban ecology, environmental science, and medical research to systematically summarize the species composition of allergenic pollen in urban green spaces, their spatial and temporal distribution characteristics, monitoring technologies, and risk assessment methods.

Results The results indicate that research on allergenic pollen has grown steadily worldwide over the past two decades, with international publications showing a significant upward trend and reaching a peak around 2016. In contrast, the annual number of domestic publications in China remains relatively limited but has gradually increased. Bibliometric analysis reveals that early research in this field mainly focused on immunological mechanisms and clinical treatments of allergic diseases, including studies on monoclonal antibodies, IgE binding, cloning techniques, and allergen-specific immunotherapy. However, during the past decade, research hotspots have shifted toward airborne pollen sources, environmental drivers, health risk assessments, and the effects of climate change and air pollution. Keywords such as airborne pollen, allergenic pollen, risk, and climate change have shown strong burst intensity, indicating that understanding pollen sources, spatial-temporal distribution patterns, and associated health risks has become a major research frontier. Further analysis of urban green spaces reveals that allergenic pollen mainly originates from wind-pollinated plants, including species from families such as Salicaceae, Pinaceae, Cupressaceae, Betulaceae, Ulmaceae, and Asteraceae. The composition of allergenic pollen species varies significantly across regions due to differences in vegetation structure and climatic conditions. In northern Chinese cities, major allergenic pollen sources include Salicaceae, Pinaceae, and Betulaceae species, while southern cities are dominated by coniferous species and grasses. Temporally, allergenic pollen concentrations typically exhibit strong seasonal patterns, with a major spring peak from tree pollen and a secondary autumn peak from herbaceous plants. Spatially, pollen concentrations show considerable heterogeneity within cities, influenced by green space size, vegetation composition, urban morphology, and local meteorological conditions. In terms of monitoring technologies, two primary methods are widely used: gravity deposition sampling and volumetric sampling. Traditional microscopic identification remains the standard approach for pollen classification, although it often achieves only genus-level resolution. In recent years, automated pollen monitoring systems integrating laser optics, machine vision, and artificial intelligence have been developed to enable real-time pollen detection and classification. Regarding risk assessment, current approaches can generally be categorized into three main types: pollen concentration-based assessments, allergen-based assessments, and vegetation-based allergenicity index models. Each approach provides different insights into pollen exposure and allergenic risk, but their integration remains limited. Several challenges remain, including insufficient taxonomic resolution in pollen identification, inconsistencies among monitoring standards, and the lack of integrated frameworks that combine environmental, ecological, and human exposure factors.

Conclusion Research on urban allergenic pollen is gradually transitioning from traditional monitoring and descriptive analysis to more comprehensive studies integrating ecological mechanisms, environmental drivers, and human health effects. Future research should prioritize improving species-level pollen identification through advanced microscopy and molecular techniques, establishing standardized monitoring networks and unified classification systems for pollen concentration, and developing integrated risk assessment frameworks that incorporate vegetation composition, urban spatial structure, climate conditions, and population exposure patterns. The integration of remote sensing, geographic information systems, and multi-source spatial data also offers promising opportunities for high-resolution modeling and forecasting of pollen distribution and allergic risk. By combining ecological knowledge with public health perspectives, future studies can support the development of health-oriented urban green space planning and management strategies, thereby reducing allergenic pollen exposure while maintaining the ecological benefits of urban vegetation.