Yu Wang  1,2, Changchang Li3, Zengliang Ruan4, Rouxuan Ye5, Bin Yang This email address is being protected from spambots. You need JavaScript enabled to view it.1,2, Hung Chak Ho This email address is being protected from spambots. You need JavaScript enabled to view it.6,7,8 

1 Department of Dermatology, Jinan University First Affiliated Hospital, Guangzhou 510632, China
2 Department of Dermatology, Dermatology Hospital of Southern Medical University, Guangzhou 510091, China
3 STD Control Department, Dermatology Hospital of Southern Medical University, Guangzhou510091, China
4 Department of Epidemiology and Health Statistics, School of Public Health, Southeast University, Nanjing 210096, China
5 Department of Biostatistics, Bioinformatics & Biomathematics, Georgetown University, Washington, DC 20007, USA
6 Department of Anesthesiology, School of Clinical Medicine, The University of Hong Kong, Hong Kong
7 Healthy High Density Cities Lab, Faculty of Architecture, The University of Hong Kong, Hong Kong
8 Department of Urban Planning and Design, The University of Hong Kong, Hong Kong

Received: April 7, 2022
Revised: June 16, 2022
Accepted: June 17, 2022

 Copyright The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are cited.

Download Citation: ||https://doi.org/10.4209/aaqr.220166  

  • Download: PDF

Cite this article:

Wang, Y., Li, C., Ruan, Z., Ye, R., Yang, B., Ho, H.C. (2022). Effects of Ambient Exposure to Nitrogen Dioxide on Outpatient Visits for Psoriasis in Rapidly Urbanizing Areas. Aerosol Air Qual. Res. https://doi.org/10.4209/aaqr.220166


  • Rapidly urbanized areas with high population density may have moderate air quality.
  • Moderate air quality may not exceed the limit of national air quality standard.
  • A moderate level of short-term NO2 exposure may induce risk of psoriasis.
  • NO2 emission had a prolonged effect on outpatient visits for psoriasis.
  • Older adults and individuals with medical insurance coverage have higher risks.


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-µg m-3 increase in NO2 concentration could still be associated with 3.1% higher outpatient visits for psoriasis (adjusted RR of lag 0 d: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, O3, and meteorological factors, a 10-µg 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.

Keywords: Air pollution, Nitrogen dioxide, Psoriasis, Outpatient visits

Share this article with your colleagues 


Subscribe to our Newsletter 

Aerosol and Air Quality Research has published over 2,000 peer-reviewed articles. Enter your email address to receive latest updates and research articles to your inbox every second week.

Aerosol and Air Quality Research (AAQR) is an independently-run non-profit journal that promotes submissions of high-quality research and strives to be one of the leading aerosol and air quality open-access journals in the world. We use cookies on this website to personalize content to improve your user experience and analyze our traffic. By using this site you agree to its use of cookies.