Particulate matter, nitrogen dioxide, and sulfur dioxide and their associations with allergic skin diseases: A systematic review and meta-analysis

Ambient air pollution is a significant global cause of human diseases. However, the association between exposure to air pollutants and the incidence of allergic skin diseases in humans, particularly children, remains inconclusive. This review summarized the effects of exposures to main air pollutants - particulate matter with fine particles (PM2.5) and coarse particles (PM10), nitrogen dioxide (NO2), and sulfur dioxide (SO2) on the three main allergic skin diseases (urticaria, eczema, and atopic dermatitis) through a systematic meta-analysis. A Risk of Bias (RoB) instrument was used to evaluate the included studies and an adapted assessment framework for each exposure-outcome combination to assess the certainty of evidence. Random-effects models were conducted in meta-analysis, and we included a total of 59 studies published between 1998 and 2021 in the review from eleven countries. The pooled results suggested that the summary odds ratio (OR) of main skin diseases and PM10 was determined to be 1.05 (95% confidence interval (CI) = 1.03–1.08), and 1.07 (95% CI = 1.02–1.13), 1.11 (95% CI = 1.06–1.17), and 1.06 (95% CI = 1.02–1.10) for PM2.5, NO2, and SO2, respectively. Meanwhile, NO2 (pooled OR = 1.15; 95% CI = 1.08–1.22; I2 = 84%) was found to have a stronger association with eczema for children (under 18 years old) compared to PM2.5, PM10, and SO2. Furthermore, the results suggested an estimated concentration threshold of air pollutants for the incidence of allergic skin diseases, 67.34 μg/m3 for PM10 and 43.00 μg/m3 for PM2.5. Overall, the incidence of atopic dermatitis, eczema, and urticaria increased globally due to the exposure to ambient air pollutants (PM2.5, PM10, NO2, and SO2). In general, the associations found in this study are reliable with a high level of certainty.