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European Journal of Dermatology

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Proposal for a new UVA protection factor: use of an in vitro model of immediate pigment darkening Volume 12, issue 5, September - October 2002

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Authors
Bioderma, 75, cours A.-Thomas, 69447 Lyon Cedex 3, France.

In order to define a new method for measuring UVA photoprotection, we built an in vitro immediate pigment darkening model (IPD). IPD is a photochemical reversible reaction induced by UVA on the skin. Our model consists of aqueous solutions of melanocytic compounds (dihydroxyphenylalanine/pheomelanins). Irradiation of these solutions with UVA induces an increase in their absorbance. Oxygen deprivation inhibits the solution darkening and light turn-off induces a decrease in the absorbance as observed in vivo. A UVA photoprotection parameter (Puva) was defined using the ability of a sunscreen to inhibit the model reaction. A calibration of the reaction inhibition is realised using neutral beam attenuators. Puva is defined as the percentage absorbance of a beam attenuator which would have the same inhibitory effect as the sunscreen tested. A correlation between Puva and Diffey-Robson parameter is presented. The method developed here could be use as a indicative tool before human experiments.