Cutaneous UVB Irradiation Alters Gut Microbiota Independently of Skin Inflammation in SKH-1 Hairless Mice

This study investigates the impact of chronic ultraviolet B (UVB) exposure on gut microbiota composition and skin inflammation. Mice were subjected to a 12-week regimen of low-dose UVB irradiation designed to mimic mild photoaging. Although no significant changes were observed at the phylum level, UVB exposure resulted in a significant decrease in the genus <i>Lactobacillus</i> (<i>P</i>=0.0302) and an increase in <i>Duncaniella</i> (<i>P</i>=0.046), accompanied by a reduction in α-diversity. At the species level, <i>Lactobacillus johnsonii</i>, a known probiotic, was significantly decreased, while <i>Duncaniella freteri</i> was increased in the UVB-exposed group. Despite these microbial alterations, no significant skin inflammation was detected, as mRNA levels of interleukin (IL)-1β and TNF-α and protein levels of IL-1β and IL-2 remained unchanged. These findings suggest that chronic low-dose UVB exposure can alter gut microbial homeostasis independently of local inflammatory responses, highlighting a potential role for the skin-gut axis in mediating systemic effects of environmental UVB exposure.