Abstract This exploratory in vivo study investigated the impact of solar‐simulated ultraviolet (UV) radiation (UVB plus UVA) on the composition of the human skin microbiome in healthy male volunteers. Thirty Caucasian men were exposed to suberythemal and erythemal doses of UV radiation (0.5, 0.7, and 1.0 minimal erythema dose, MED) on defined areas of the lower back. Skin swabs were collected from both irradiated ( n = 243) and nonirradiated control sites ( n = 81) 30 min, 24 h, and 96 h postexposure. The microbial profiles were generated using flow cytometry, and the data were analyzed via the open‐access bioinformatic platform FlowSoFine™. The results revealed pronounced alterations in the microbial composition, with changes already detectable 30 min after exposure. Although partial recovery was observed over time, certain microbial shifts persisted. Further analysis indicated dose‐dependent trends in microbiome changes, suggesting a potential relationship between the extent of microbial alteration and the applied UV dose. These results suggest that even low, nonerythematous exposure to solar‐simulated UV radiation can rapidly alter the microbial balance of the skin and emphasize the role of UV radiation as a potent modulator of the skin microbial homeostasis.
Dimmers et al. (2026) studied this question.