Experiments conducted in mouse and human cells suggest that UV radiation–induced DNA lesions can occur in melanin-producing cells more than 3 hours after sunbathing or tanning (Premi S et al. Science. 2015;347:842-847).
The DNA lesions induced by UV radiation exposure, known as cyclobutane pyrimidine dimers (CPDs), structurally distort DNA and interfere with replication. Yale University School of Medicine researchers and their colleagues found that human and mouse melanocytes, which make the skin pigment melanin, generated CPDs immediately and continued to do so hours after UV exposure ended. Melanocytes without melanin generated CPDs only during UV exposure.
Hampton T. DNA Damage Continues Long After Sun Exposure. JAMA. 2015;313(13):1305. doi:10.1001/jama.2015.2856