Association of air quality index (AQI) with incidence of atopic dermatitis in Taiwan: A nationwide population-based cohort study

Background: Air pollutants may aggravate atopic dermatitis (AD). However, the association between Air Quality Index (AQI) and incidence of AD remains unknown. Objective: To investigate association between AQI and incidence of AD, using the nationwide cohort in the Taiwan National Health Insurance Research Database (NHIRD). Methods: We included 21,278,938 participants from the NHIRD not diagnosed with AD before 2008. Long-term average AQI value, obtained from the Taiwan Air Quality Monitoring System Network, before AD diagnosis was calculated and linked for each participant. Results: 199,205 incident cases of AD were identified from 2008 to 2018. Participants were classified into 4 quantiles (Q) by AQI value. With the lowest quantile, Q1, as reference, the AD risk increased significantly in the Q2 group (adjusted hazard ratio [aHR]: 1.29, 95% confidence interval [CI]: 1.04-1.65), Q3 group (aHR: 4.71, 95% CI: 3.78-6.04), and was highest in the Q4 group (aHR: 13.20, 95% CI: 10.86-16.60). As AQI treated as a continuous variable, an increase of 1 unit of AQI value added 7% of AD risk (aHR, 1.07, 95% CI: 1.07-1.08). Limitations: The NHIRD lacks detailed information on individual subjects. Conclusions: The results demonstrated a significant positive association between AQI and incidence of AD with a clear dose-response relationship.