206 JOURNAL OF COSMETIC SCIENCE The last common approach is to take advantage of the fact that melanogenesis is an oxidative process. Highly reactive antioxidants such as ascorbic acid can be used to compete with melanin precursors for the oxidative stress available to the system. This approach not only inhibits the production of melanin, but can reduce the amount of melanin already present in the skin. Most commonly used skin-lightening ingredients share a common problem. Most skin- lightening ingredients tend to be unstable in typical cosmetic formulations. Some lighteners such as hydroquinone also demonstrate significant toxicity. In order to maximize the whitening effects while minimizing possible toxicity or formulation incompatibilities it is important to use a multifaceted approach. The first step in optimizing a skin-lightening formulation is to select actives that will cover several routes ofmela-nogenesis. Initially a broad spectrum sunscreen must be selected. While it may take months to alleviate pigmentation, it may only take one day in the sun to regenerate it. UV filters will also help to improve the stability of any photo-labile actives present. Having selected a sunscreen it is now important to apply a combination of tyrosine inhibitors and antioxidants. The question remains. How do you take a cocktail of commonly used skin lightening agents and significantly increase the activity? The answer lies in the field of potentiation. By stimulating cell activity it is clearly possible to influence the pigmentation process. Just as cyclic AMP agonists can accelerate tannihg, materials that increase cell respiration can reduce melanogenesis. Many ingredients such as Sacchromyces ferment extract or Clintonia boreallis extract increase cell respiration. These potentiators do not increase the amount of oxygen available to the cell, but increase the efficiency with which the cell utilizes the oxygen. Increase efficiency in oxygen utilization translates to increased efficiency in other process. Activation of fibroblasts reduces the rate of melanogenesis. Activation of keratinocytes increases the speed at which melanin is eliminated from the skin. Potentiators in conjunction with more traditional approaches to skin lightening offer a revolutionary approach to skin lightening. The future of research for skin lightening should not focus on looking for new specific lightening agents, but at potentiating the natural processes which can inhibit melanogenesis. References 1. G. Prota, Melanins and melanogenesis, Academic Press, London 1992. P. Aroca, K. Urabe,T. Kobayashi, K Tsukamoro, and V. J. Hearing, Melanin biosynthesis patterns following hormonal stimulation, J. Biol Chem 268 (34) 25650 (1993) J. R. Jara, F. Solano, J. C. Garcia-Borron, P. Aroca, J. A. Lozano, Regulation of mammalian melanogenesis. II the role of metal cations. Biochim Biophys Acta 1035: 276-85 (1990) 4. M.T. McEwan, P. G. Parsons, Regulation oftyrosinase expression and activity in human melanoma cells via histamine receptors. J Invest Dermato197:868-73 (1991)

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