The role of the skin microbiome in UV-induced immune suppression has been overlooked. We addressed the question of microbial involvement in UV-induced immune suppression by using the standard model of contact hypersensitivity in the presence or absence of the microbiome (in germ-free [GF] and disinfected mice) and found that the microbiome inhibits UV-induced immune suppression. Furthermore, our transcriptome analysis (24 hours after irradiation) showed differential regulation of many genes in the presence or absence of the microbiome, including a predominance of pro-inflammatory cytokines versus immunosuppressive cytokines Overall design: 3 mice per experimental group