PCR-based methodology for the determination of the photoprotection afforded by sunscreen application.

We have applied a PCR-based methodology to study the DNA damage induced by UV-A, UV-B and sunlight itself. Our results, employing a cell-free system, indicate that UV-B (310 nm) is approximately 30-fold more potent at inhibiting DNA synthesis than UV-A (365 nm). We were also able to show that 20 min of sunlight exposure on a summer day induced DNA damage capable of inhibiting DNA synthesis. Hence, this methodology has a sensitivity suitable to detect biologically relevant doses of UV light. In addition, we propose that this technique may be suitable to assess the relative photoprotection of commercially available sunscreens. We present here preliminary data on the photoprotection afforded by the topical application of sunscreen. This photoprotection was measured by a reduction in the subsequent UV-B- and UV-A-induced DNA damage when sunscreen was applied. Our results demonstrate that the particular sunscreen tested was effective against both UV-B and UV-A. However, the estimated photoprotective factor of the sunscreen (against both UV-A and UV-B) was approximately tenfold less than the stated Sun Protection Factor (SPF) of 25. This methodology may also be useful in identifying new photoprotective agents by assessing their relative value as UV-B and UV-A absorbing agents.