Abstract: Objective: To evaluate the effect of air pollutants (SO2, NO2, PM2.5, PM10 and O3) on daily outpatient visits for urticaria. Methods: CNKI, VIP, WanFang Data, VIP, CBM, The Cochrane Library, PubMed, EMbase and Web of science were searched to collect the literatures about air pollutants on daily outpatient visits for urticaria from the establishment of the bank to October 2018. Two reviewers independently screened literature, extracted data and assessed the quality of included studies. Results: A total of 5 cross-sectional studies were included, but Meta analysis was not done, because the unanticipated heterogeneity and only the qualitative description were made. Of the 5 studies, particulate matter ( PM2.5, PM10) were exposure factors in 3 studies, SO2 and NO2 were exposure factors in 2 studies, O3 is a exposure factor in one study. In addition, Air Quality Index (AQI) calculated on the basis of pollutant concentration as the exposure factor in two other literatures. Conclusion: The air pollutants may contribute to daily outpatient visits of urticaria. 

Key words: air pollutants, urticaria, cross-sectional studies, systematic review