Effects of Ambient Exposure to Nitrogen Dioxide on Outpatient Visits for Psoriasis in Rapidly Urbanizing Areas

Rapid development and urbanization can increase ambient exposure to NO2 and its health risks in individuals. However, the association between NO2 exposure and outpatient visits of patients with psoriasis has rarely been reported, though psoriasis is a major skin disease in rapidly urbanizing areas with high population densities. This study applied a time-stratified case-crossover design to investigate the effect of short-term exposure to ambient NO2 on outpatient visits for psoriasis from 2014 to 2020 in Guangzhou, China (n = 62,305). A subgroup analysis was performed to evaluate NO2 impacts on vulnerable subpopulations. Our results showed that the NO2 concentration during the study period was lower than that of the level II threshold from China (PRC) but higher than that set by the WHO, indicating moderate air quality. However, a 10-mu g m(-3) increase in NO2 concentration could still be associated with 3.1% higher outpatient visits for psoriasis (adjusted RR of lag 0 day:1.031 [CI: 1.025, 1.037]). NO2 exposure can also pose long-term risks. Additionally, NO2 impacts on psoriasis may be independent of other pollutants. Adjusting for PM2.5, SO2, O-3, and meteorological factors, a 10-mu g m(-3) increase in NO2 was associated with RRs of 1.043 [CI: 1.033, 1.053], 1.022 [CI: 1.014, 1.031], and 1.022 [CI: 1.014, 1.031] at lag 0, lag 1, and lag 2 days, respectively. NO2 risks were higher among older individuals (age >= 60 years) and those with medical insurance [adjusted RRs: 1.045 (CI: 1.023, 1.066) and 1.047 (CI: 1.036, 1.058)]. Being a major pollutant in rapidly urbanizing areas with high population densities, NO2 emission could be a crucial factor in psoriasis, although the daily pollution level was not above the air quality thresholds. Challenges associated with air quality control and health disparity create a necessity for the enhancement of health and environmental policies to reduce local and regional emissions (e.g., traffic-related pollution), and vulnerable subpopulations should be targeted.