Objective Allergic diseases are immune-related diseases, and their incidence rate is increasing. The decrease in the contact between natural environment and biodiversity caused by the decline of global ecological environment quality is an important factorfor their high incidence. As an important part of the ecosystem, green space is an important carrier facilitating contact between natural environment and biodiversity, and its impact on allergic diseases is increasingly concerned. A deep understanding of the relationship between green space biodiversity and allergic diseases can not only provide a theoretical basis for exploring the relationship between cities, ecology, and health in the process of rapid urbanization, but also provide a practical approach for improving the ecological environment quality of national land and improving health service functions.

Methods Based on literature retrieved from Web of Science and PubMed up to 2025, this review selected empirical studies examining the relationship between green space, its biodiversity, and allergic diseases. A systematic synthesis was conducted to summarize research methods, findings, and underlying mechanisms concerning the impact of green space and its biodiversity on allergic diseases.

Results Firstly, in terms of research methods, a total of 16 studies used cohort analysis, 12 studies used cross-sectional analysis, and 2 studies used case-control designs. These documents reveal a correlation between green space biodiversity and allergic diseases. Cohort studies, using long-term time-series data, can reveal the cumulative effects of biodiversity on allergic diseases to some extent. However, such studies mainly focus on the macro-level supply characteristics of green spaces, and the measurement of biodiversity is still relatively coarse. Moreover, there is limited empirical evidence on the impact of microbial diversity as the mediating factor. Cross-sectional studies can analyze the comprehensive impacts of demographic, socioeconomic, and environmental factors on allergic diseases by incorporating more refined green space biodiversity indicators and more comprehensive control variables. However, they cannot distinguish causal temporal relationships. Case-control studies have time and economic cost advantages compared to cohort studies. However, current case-control studies have included only availability and accessibility indicators that reflect the overall characteristics of green spaces, and have not provided clear or specific measurements of green space biodiversity. Secondly, the analysis of the impact results shows that there are certain differences in the results. Indicators related to plant diversity and tree species composition are associated with a reduced risk of allergic diseases, while indicators related to grasslands, coniferous trees, and non-native plants are associated with an increased risk of allergic diseases. However, there are significant differences in the research conclusions of indicators reflecting overall supply characteristics. The inconsistency of research conclusions may mainly be caused by differences in research design, exposure assessment, control variables, and geographical regions. Thirdly, in terms of influencing mechanisms, the impact mechanism of green space biodiversity on allergic diseases may stem from its key role in maintaining ecological community stability and preventing species imbalance. The existing theoretical hypothesis has jointly revealed the basic relationship between green space biodiversity and allergic diseases: under the background of urbanization, the environmental and lifestyle changes, the reduction of macro-biodiversity and of human contact with green space and other natural environments and biodiversity, which led to the reduction of microbial diversity contact level, hinders immune regulation circuits, and leads to a sharp rise in the incidence rate of allergic diseases. Appropriate environmental microbial exposure can be achieved by restoring urban green spaces, potentially reducing the incidence of allergic diseases may be reduced. However, the role of green space biodiversity in maintaining community species balance, preventing microbial dysbiosis, and inhibiting single species dominance, as well as the empirical verification of the mediating role of microbial diversity between macro biodiversity and allergic diseases, are not sufficient.

Conclusion The exiting studies have deficiencies in the measurement of green spaces and their biodiversity indicators, the exploration of complete influence paths and mechanisms. The research on the influence mechanism is a significant gap, and the research conclusions are heterogeneous. Future research can focus on the differentiated roles of fine-grained green spaces and their biodiversity indicators, explore the regulatory effect of green space biodiversity on the balance between species, analyze the key mediating role of microbial diversity, and pay attention to environmental and population differences.