Association between air quality index and risk of alopecia areata: A nationwide population-based cohort study

Abstract Background Air pollution is associated with several inflammatory skin disorders. However, the relationship between air quality index (AQI) and alopecia areata (AA) remains unclear. Objective To investigate the association between AQI and incidence of AA. Methods 21,727,991 participants without AA before 2008 were recruited from the Taiwan National Health Insurance Research Database (NHIRD). The long-term exposure of average AQI values for each participant were acquired from the Taiwan Air Quality Monitoring System Network and calculated before AA diagnosis. Results A total of 61,637 incident cases of AA were identified from 2008–2018. With the best AQI value, Q1, as a reference, the risk of AA increased significantly in the Q2 group (adjusted hazard ratio [aHR]: 1.44, 95% confidence interval: 1.21–1.79), Q3 group (aHR: 3.47, 95% CI: 2.86–4.34), and was highest in the Q4 group (aHR: 6.18, 95% CI: 5.20 ~ 7.38). As AQI was treated as a continuous variable, an increase in one unit of AQI increased the risk of AA by 5% (aHR: 1.05, 95% CI: 1.05–1.05). Conclusions We observed a significant positive association between the AQI and the incidence of AA, with a clear dose-response relationship.