Sunscreens block the induction of unscheduled DNA synthesis and the inhibition of DNA synthesis by UV-B radiation in normal human fibroblasts. A new way of evaluating sunscreen efficacy in vitro.

In order to evaluate the photoprotective efficacy of sunscreens against the chronic actinic damage, we tested 3 sunscreens for their ability to reduce the induction of unscheduled DNA synthesis (UDS) and to prevent the inhibition of semi-conservative DNA synthesis by medium wavelength ultraviolet (UV-B) radiation in the normal human cultured fibroblasts in vitro. The values obtained are correlated with the sun protection factors (SPF) expressing the erythema inhibition in normal human skin. All sunscreens tested showed a protective effect. The protective factor for the induction of UDS is 10.1 for Spectraban 15 (SPF 15), 3.6 for Spectraban 5.6 (SPF 5.6) and 1.9 for 2.5% Indomethacin solution, whereas the protective factor for the inhibition of semi-conservative DNA synthesis of 15.2, 3.9 and 2.1 for each sunscreen was evaluated. These methods seem to be useful as a screening procedure for the evaluation of sunscreen effectiveness against chronic actinic skin damage including light induced skin malignancies.