The Toxin of the Year: Airborne PM2.5.

Particulate matter (PM) with a diameter of 2.5 µm or smaller (PM2.5) has emerged as a critical environmental toxin affecting skin health. In light of its widespread and often underestimated impact, we designated PM2.5 as the "toxin of the year." Although PM2.5 primarily affects the respiratory system, growing evidence indicates that it also plays a significant role in cutaneous health. Exposure to PM2.5 can lead to oxidative stress, inflammation, and impairment of the skin barrier, particularly in individuals with preexisting skin conditions. An increasing number of studies highlight an association between PM2.5 exposure and the prevalence and exacerbation of inflammatory skin diseases such as atopic dermatitis and psoriasis. This review therefore focuses on the fundamental mechanisms, including key molecular pathways, by which PM2.5 contributes to skin damage, with an emphasis on its role in the onset and progression of inflammatory skin diseases, as evidenced by population-based studies. A deeper understanding of these processes is crucial for guiding the development of targeted prevention and therapeutic strategies in response to raising environmental pollution. Giving the growing body of evidence, this review aims to consolidate current knowledge and highlight critical gaps in our understanding of PM2.5 impact on inflammatory skin diseases.