Cosmeceuticals.

The author uses kinetin, a plant-derived nucleotide, as an example to summarize the approach to advising a patient on a new product. (1) Does it penetrate the stratum corneum? Topically applied nucleotides can penetrate human skin, and one of the most active and useful of these for the treatment of actinic keratoses, 5-fluorouracil (5-FU), is used widely in dermatology. 5-FU derives some of its benefit from its uptake, specifically in actinic keratoses, which do not have a complete epidermal barrier. The molecule is able to penetrate the stratum corneum. It is not clear that topically applied nucleotides have the same degree of penetration on photodamaged skin without actinic keratoses. (2) Is there a plausible biochemical mechanism of action? 5-FU has a well-known mechanism of action (i.e., the inhibition of DNA/RNA synthesis by incorporation of a false pyrimidine analog). The mechanism of action for furfuryladenine in human skin remains unknown and needs to be shown. If furfuryladenine functions as an antioxidant, it may be useful as a photoprotectant. This function does not account for a mechanism of action for the reversal of photoaging, however. (3) Are there published peer-reviewed, double-blinded, placebo-controlled, statistically significant clinical trials to substantiate the efficacy claim? Peer-reviewed, double-blinded, statistically significant clinical trials on furfuryladenine have not been published to date. The field of cosmeceuticals presents a quandary. The list of cosmeceuticals for the dermatologist to assess grows longer each year. It is possible that some of the active ingredients are beneficial physiologically in human skin and that they can offer specific benefits, such as photoprotection. Further research needs to be conducted to validate these claims. It also is likely that a wide variety of molecules purported to be active in human skin do not have any physiologic benefit in human skin. Only further research can answer these difficult questions.