Association Between Short-term Exposure to Environmental Air Pollution and Psoriasis Flare

IMPORTANCE: Psoriasis is a chronic inflammatory disease with a relapsing-remitting course. Selected environmental factors such as infections, stressful life events, or drugs may trigger disease flares. Whether air pollution could trigger psoriasis flares is still unknown. OBJECTIVE: To investigate whether short-term exposure to environmental air pollution is associated with psoriasis flares. DESIGN, SETTING, AND PARTICIPANTS: This observational study with both case-crossover and cross-sectional design retrospectively analyzed longitudinal data from September 2013 to January 2020 from patients with chronic plaque psoriasis consecutively attending the outpatient dermatologic clinic of the University Hospital of Verona. For the case-crossover analysis, patients were included who had at least 1 disease flare, defined as Psoriasis Area and Severity Index (PASI) increase of 5 or greater between 2 consecutive assessments in a time frame of 3 to 4 months. For the cross-sectional analysis, patients were included who received any systemic treatment for 6 or more months, with grade 2 or higher consecutive PASI assessment. MAIN OUTCOMES AND MEASURES: We compared the mean and cumulative (area under the curve) concentrations of several air pollutants (carbon monoxide, nitrogen dioxide, other nitrogen oxides, benzene, coarse particulate matter PM; 2.5-10.0 μm in diameter, PM10 and fine PM <2.5 μm in diameter, PM2.5) in the 60 days preceding the psoriasis flare and the control visits. RESULTS: A total of 957 patients with plaque psoriasis with 4398 follow-up visits were included in the study. Patients had a mean (SD) age of 61 (15) years and 602 (62.9%) were men. More than 15 000 measurements of air pollutant concentration from the official, open-source bulletin of the Italian Institute for Environmental Protection and Research (ISPRA) were retrieved. Among the overall cohort, 369 (38.6%) patients with psoriasis flare were included in the case-crossover study. We found that concentrations of all pollutants were significantly higher in the 60 days before psoriasis flare (median PASI at the flare 12; IQR, 9-18) compared with the control visit (median PASI 1; IQR, 1-3, P < .001). In the cross-sectional analysis, exposure to mean PM10 over 20 μg/m3 and mean PM2.5 over 15 μg/m3 in the 60 days before assessment were associated with a higher risk of PASI 5 or greater point worsening (adjusted odds ratio aOR, 1.55; 95% CI, 1.21-1.99; and aOR, 1.25; 95% CI, 1.0-1.57, respectively). Sensitivity analyses that stratified for trimester of evaluation, with various lag of exposure and adjusting for type of treatment, yielded similar results. CONCLUSIONS AND RELEVANCE: The findings of this case-crossover and cross-sectional study suggest that air pollution may be a trigger factor for psoriasis flare.