Short-term air pollution exposure is associated with an increased risk for a psoriasis flare, according to study data published in JAMA Dermatology.

The finding is based on a retrospective analysis of patients with chronic plaque psoriasis from a dermatology unit of a university hospital in Verona, Italy, from September 2013 to January 2020.

A case-crossover analysis evaluated the temporal association between psoriasis flare and short-term exposure to air pollutants as cumulative area under the curve exposure in the 60 days preceding 2 consecutive dermatologic visits.

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A cross-sectional analysis included patients with any continuous systemic treatment for at least 6 months before a dermatologic visit, 2 or more consecutive measurements of Psoriasis Area and Severity Index (PASI), and residency according to zip code within 10 km of the air pollutant collection point. PASI measurements were correlated with pollutant concentrations from the preceding 60 days with adjustment for seasonality and systemic conventional or biologic antipsoriatic treatment.

Data from 957 patients with 4,398 follow-up visits and more than 15,000 measurements of air pollutant concentrations were obtained. The participants had a mean (SD) age of 61 (15) years, a mean (SD) disease duration of 24 (17) years, and 62.9% were men. Visits were conducted every 3 to 4 months during a median follow-up of 2.7 years (interquartile range [IQR], 1.1-5.2).

The patients were exposed to an average concentration of 0.34 μg/m3 CO, 28.87 μg/m3 NO2, 44.66 μg/m3 NOx, 0.57 μg/m3 C6H6, 29 μg/m3 PM10, and 21 μg/m3 PM2.5.

The case-crossover analysis included 369 (38.6%) patients with at least 2 consecutive visits, 1 psoriasis flare, and continuous systemic treatment for at least 6 months. In this group, the median PASI at the flare visit (12; IQR, 9-18) was significantly higher vs the median PASI at the control visit (1; IQR, 1-3), P <.001). Air pollutant concentrations were higher in the 60 days before the flare visit compared with the control visit.

The cross-sectional analysis included 4,072 visits from 957 patients. Exposure to a mean particulate matter 10 (PM10) that is larger than 20 μg/m3 and a mean particulate matter 2.5 (PM2.5) that is larger than 15 μg/m3 was associated with 50% and 25% increased risk of having an absolute PASI score of 5 or higher, respectively (adjusted odds ratio [aOR] 1.55; 95% CI, 1.21-1.99; and aOR 1.25; 95% CI, 1.0-1.57; respectively). The association was not evident at thresholds of 15 μg/m3 for PM10 and 10 μg/m3 for PM2.5.

Subgroup analyses with stratification based on trimester of visit to adjust for the season yielded similar findings.

Study limitations include the definition of flare, which was based on a clinical score rather than an objective laboratory parameter such as C-reactive protein. Also, the investigators indicated that they did not have access to annual weather conditions to adjust for ultraviolet sunlight exposure, and they did not consider the potential influence of topical treatments or stressful and infective events. Furthermore, they did not have data regarding indoor pollution, initiation/cessation of smoking, and respiratory comorbidities.

“Further study is needed to examine whether these findings generalize to other populations and to better understand the mechanisms by which air pollution may affect psoriasis disease activity,” the investigators commented.

Disclosure: Some of the study authors declared affiliations with biotech, pharmaceutical, and/or device companies. Please see the original reference for a full list of authors’ disclosures.


Bellinato F, Adami G, Vaienti S, et al. Association between short-term exposure to environmental air pollution and psoriasis flare. JAMA Dermatol. Published online February 16, 2022. doi:10.1001/jamadermatol.2021.6019