Association between exposure to air pollution and risk of allergic rhinitis: A systematic review and meta-analysis

Background: Allergic rhinitis (AR) is one of the most common allergic diseases in the world, and usually persists throughout the activity. Epidemiological studies have shown a positive association between air pollution and allergic rhinitis. However, we could not find any meta-analysis of the risk of air pollutants (PM2.5, PM10, NO2, SO2, O-3 and CO) on the prevalence of AR in people of all ages. Objectives: Carry out a meta-analysis on the results of recent studies (up to 2020) to present valid information about exposure to air pollution and risk of prevalence of AR. Methods: We systematically searched three databases for studies up to December 17, 2020, including air pollution and AR. Random effect models were conducted to estimate the pooled odds ratios (ORs) and 95% confidence intervals (95% CIs). Subgroup analysis, funnel plot, Egger's test, and the trim-and-fill method were also conducted. Results: Thirty-five studies across 12 countries, including a total of 453,470 participants, were included. The OR per 10 mu g/m(3) increase of pollutants was 1.13 (1.04-1.22) for PM10 and 1.12 (1.05-1.20) for PM2.5. The OR per 10 mu g/m(3) increment of gaseous pollutants were 1.13 (1.07-1.20) for NO2, 1.13 (1.04-1.22) for SO2 and 1.07 (1.01-1.12) for O-3. No significant association was observed between CO and AR. Children or adolescents are more sensitive to air pollution than adults. The effects of PM10 and SO2 were significantly stronger in Europe than Asia. The effects of air pollutants were more significant and higher in developing countries than in developed countries, except for PM10. A significant difference of subgroup test was found between developed and developing countries of NO2. Conclusion: This meta-analysis showed a positive association between air pollution and the prevalence of allergic rhinitis, and identified geographic area and economic level as the potential modifiers for the association.