There are at least two classic photoprotective DNA damage responses that can be elicited by UV exposure: induction of melanogenesis (tanning) and enhancement of DNA repair. Both mechanisms are mediated, at least in part, by the tumor-suppressor protein and transcription factor p53. Both of these responses can be induced in vitro as well as in vivo by small DNA fragments of specific sequences, without prior induction of actual DNA damage. The topical application of such fragments onto human skin might enhance photoprotection in human skin, as typically elicited by gradual sun exposure. The induction of photoprotection by this means, however, would not bear the mutagenic and carcinogenic risk of exposure to natural sunlight.
