The cutaneous microbiome as a dynamic photoprotective interface against solar radiation.

This review reframes cutaneous photoprotection as a host–microbe system and synthesizes evidence, largely from experimental model systems and human observational studies, that resident skin microbes sense, transform, and defend against solar ultraviolet stress. We introduce the “host-protective UV-resistome” defined as the subset of microbial genes and pathways that confer photoprotection to the host, and organize current findings into three stages: sensing of UV-related cues via pigments and redox-responsive regulators, microbial responses that mitigate damage (e.g., pigments and secreted antioxidants), and host adaptations to microbial signals that modulate immunity and barrier repair. Longitudinal and environmental studies suggest that chronic UV exposure selects for oxidative-stress-tolerant taxa, implying ecological adaptation of the skin microbiome under solar pressure. We outline testable hypotheses for photosensitive conditions and for visible-light–exacerbated pigmentary disorders. Finally, we propose translational directions for microbiome-conscious photoprotection, namely by stabilizing beneficial metabolites, supporting protective taxa with pre/probiotics, and designing formulations that preserve microbial resilience. Together, these data position the host-protective UV-resistome as a substantive, quantifiable contributor to cutaneous photoprotection.