The multilayered organization of engineered human skin does not influence the formation of sunlight-induced cyclobutane pyrimidine dimers in cellularDNA

Solar UVB initiates skin cancer mainly by generating highly premutagenic cy clobutane pyrimidine dimers (CPDs) and subsequent mutations in critical gro wth control genes. It is universally presumed that the upper epidermis in h uman skin blocks a significant portion of the incident WE, thereby protecti ng the cancer-prone basal layer from CPD formation. Using two sensitive tec hniques for measuring CPD in cellular DNA, we confirmed that the multilayer ed organization of engineered human skin efficiently shields the basal laye r against 254-mn WC (which is not present in terrestrial sunlight) but, ver y unexpectedly, provides virtually no protection against environmentally re levant WE. This underscores the importance of regular sunscreen use, which, in light of our data, may constitute a considerably more important first L ine of defense against photocarcinogenesis than previously believed.