Skin microbiome dynamics in patients with polymorphic light eruption in response to ultraviolet radiation

Background Polymorphic light eruption (PLE) is the most frequent photodermatosis in Europe, with an estimated prevalence of 10–20%, particularly in temperate climates. Itching or burning lesions appear only in sun-exposed areas, predominantly on the chest, arms and forearms, within a few hours following exposure. The cause of the disease remains unknown, yet studies have suggested that microbial elements in the skin may play a role in its pathogenesis. Objectives To investigate the skin microbiome of a cohort of patients with PLE upon exposure to ultraviolet radiation (UVR), to assess its role in the onset of PLE lesions. Methods Forty-one skin swabs were collected from 11 patients with PLE at baseline and after 3 days of exposure to UVR, and from healthy control participants. The collected swabs were analysed for their microbial composition using a 16S amplicon sequencing approach. Results PLE skin showed a dysbalanced microbiome at baseline, with significantly reduced microbial diversity and noticeable colonization by bacterial pathogens, including Staphylococcus aureus. Upon UVR exposure, the PLE microbiome exhibited further loss of diversity and a reduction in beneficial skin commensals. In line with this, we found that UVR exerted strong antimicrobial effects in vitro against representative skin residents. Conclusions UVR can lead to profound changes in the skin microbiome, allowing the proliferation of dysbiotic members that can release a variety of elements able to trigger PLE lesions. This is the first study to investigate the cutaneous microbiome changes in patients with PLE upon UVR exposure, offering new insights into disease pathogenesis that has so far been unexplored.