“ The evidence surrounding exposure to air pollution and the risk to human health is increasing at an alarming rate,” explains Francesco Bellinato, MD. “After inhalation, pollutants circulate within the bloodstream, where they can cause oxidative damage and inflammation. Moreover, when air pollutants come into direct contact with the skin, they may exacerbate inflammatory cutaneous diseases. Worsening of different inflammatory cutaneous diseases (eg, acne) have been linked air pollution exposure. We know that select environmental factors, such as infections and/or medications, may trigger disease flares. However, little is known about the effect of air pollution on psoriasis.”

For a study published in JAMA Dermatology, Dr. Bellinato and colleagues researched whether exposure to air pollution is linked with psoriasis flares. “We retrospectively analyzed clinical data on patients with chronic plaque psoriasis from EMRs from September 2013 to January 2020,” says Dr. Bellinato. “Daily concentrations of air pollutant were collected from the Po valley in Italy’s Verona region. We compared the 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 psoriasis flare and control visits.”

Concentrations of Pollutants Considerably Higher Prior to Flares

In addition, the researchers conducted case-crossover and cross-sectional analyses. “For the case-crossover analysis, we included patients who had at least one psoriasis flare, defined as a Psoriasis Area and Severity Index (PASI) increase of 5 or greater between two consecutive assessments within 3-4 months,” says Dr. Bellinato. Data on 957 patients with psoriasis with 4,398 follow-up visits were analyzed. More than 15,000 measurements were taken of air pollution concentrations.

The study team found exposure to air pollution to be correlated with greater psoriasis exacerbation. “We found that concentrations of all air pollutants of interest were significantly higher in the 60 days prior to psoriasis flares compared with the control visits,” Dr. Bellinato says. “In the cross-sectional analysis, exposure to mean PM10 greater than 20 μg/m3 and mean PM2.5 greater than 15 μg/m3 in the 60 days before assessment were associated with a higher risk for a PASI score higher than 5 (Figure).” Interestingly, he adds, the researchers observed that this risk was elevated even at thresholds of exposure that are considered safe.

Other Psoriasis Cohorts Need to Be Investigated

Key to the investigation, Dr. Bellinato notes, was the role of exogenous factors in psoriasis exacerbation, particularly in polluted areas. “Whether avoidance of exogenous triggers (ie, moving to non-polluted areas) might ameliorate psoriasis flares is a future topic of interest,” he says.

In discussing limitations of the study, Dr. Bellinato explains that the researchers did not have access to information on indoor pollution, participants’ smoking habits, or whether patients had any respiratory comorbidities. Also, the study was conducted in a highly polluted area, and thus, the results may not apply to other psoriasis cohorts. “Further studies are needed to confirm whether our findings are generalizable to other populations and to better understand the mechanisms by which air pollution may affect psoriasis disease activity,” he adds.