Skin cancer rates are high and going higher even though we are spending less time outside than our ancestors, and despite defenses shaped by selection including pigmentation, tanning and induction of DNA repairases. 

An open access article that just appeared in Science Advances  finds that Staphylococcus epidermidis produces a molecule that inhibits DNA polymerase activity and dramatically decreases skin cancer in mice.  The authors say, "The present findings suggest an entirely new concept that some members of our skin microbiome may suppress tumor growth, and dysbiosis is potentially detrimental because of loss of a protective function instead of (or in addition to) a gain of a detrimental microbial community." Which in turn suggests that antibiotics or substances that change the skin microbiota might influence rates of skin cancer.  

Nakatsuji, T., Chen, T. H., Butcher, A. M., Trzoss, L. L., Nam, S.-J., Shirakawa, K. T., … Gallo, R. L. (2018). A commensal strain of Staphylococcus epidermidis protects against skin neoplasia. Science Advances, 4(2), eaao4502.

Abstract: We report the discovery that strains of Staphylococcus epidermidis produce 6-N-hydroxyaminopurine (6-HAP), a molecule that inhibits DNA polymerase activity. In culture, 6-HAP selectively inhibited proliferation of tumor lines but did not inhibit primary keratinocytes. Resistance to 6-HAP was associated with the expression of mitochondrial amidoxime reducing components, enzymes that were not observed in cells sensitive to this compound. Intravenous injection of 6-HAP in mice suppressed the growth of B16F10 melanoma without evidence of systemic toxicity. Colonization of mice with an S. epidermidis strain producing 6-HAP reduced the incidence of ultraviolet-induced tumors compared to mice colonized by a control strain that did not produce 6-HAP. S. epidermidis strains producing 6-HAP were found in the metagenome from multiple healthy human subjects, suggesting that the microbiome of some individuals may confer protection against skin cancer. These findings show a new role for skin commensal bacteria in host defense.