Long-Term Particulate Matter Exposure and Risk of Psoriasis Incidence, and Short-Term Exposure and Risk of Exacerbation: A Nationwide Cohort Study.

Psoriasis is a chronic inflammatory skin disease influenced by environmental factors, including air pollution. However, large-scale evidence from Asian populations, where particulate matter (PM) exposure is relatively high, remains limited. This study aimed to evaluate the association between long-term PM exposure and psoriasis incidence, and short-term exposure with exacerbation risk. We conducted a cohort study using the Korean National Health Insurance Service database, involving 8 396 764 individuals. Long-term exposure was assessed based on annual average concentrations of fine PM (PM2.5) and coarse PM (PM10), while short-term exposure was measured using daily PM levels matched with control days. Long-term exposure to PM2.5 and PM10 was associated with a 19% and 27% higher risk of incident psoriasis (adjusted HR 1.19 and 1.27; 95% CI 1.16-1.22 and 1.25-1.30). Short-term exposure was linked to an increased risk of psoriasis exacerbation (adjusted OR 1.03 for PM2.5, 95% CI 1.00-1.06; adjusted OR 1.01 for PM10, 95% CI 1.00-1.03). Stronger associations were observed in younger individuals, urban residents, those with lower socioeconomic status, ever-smokers, and patients with comorbid allergic diseases. These findings suggest that both long-term and short-term PM exposure contribute to psoriasis onset and exacerbation, underscoring air pollution as an important modifiable risk factor in psoriasis development and control.