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J. Cosmet. Sci., 54, 513-524 (September/October 2003) Photodegradation of phenol and salicylic acid by coated rutile-based pigments: A new approach for the assessment of sunscreen treatment efficiency DAVIDE VIONE, TATIANA PICATONOTTO, and M. EUGENIA CARLOTTI, Dipartimento di Chimica Analitica, Universit2• degli Studi di Torino, Via P. Giuria 5 (D. V., T.P.), and Dipartimento di Scienza e Tecnologia del Farmaco, Universita degli Studi di Torino, Via P. Giuria 9 (M.E.C.), 10125 Turin, Italy. Accepted for publication April 11, 2003. Synopsis The treatments used in many commercial sunscreen pigments (organic additives and inorganic surface coating) to lower the pigments' ability to degrade molecules under photocatalytic conditions are effective in inhibiting the degradation oF phenol, but much less effective towards the degradation of salicylic acid. The reason is in the different degradation pathways that phenol and salicylic acid follow under photocata- lytic conditions. The treatments are thus effective in inhibiting the degradation pathways initiated by TiIV-øOHsurf (also named øOHa,•s), as in the case of phenol, but much less effective towards electron-transfer processes involving surface complexes, as in the case of salicylic acid. These results indicate that the techniques currently adopted by the cosmetic industry to develop organic additives for use as pigment treatments are likely to be inadequate. The problem most likely is that treatments are optimized following the inhibition of the photocatalytic degradation of a single model molecule, which results in blocking just one photocatalytic degradation pathway (usually the one initiated by TiIV-'OHs•) and not the other (electron transfer processes). The possible implications for sunscreen pigments are briefly discussed, and a new approach for the evaluation of the photocatalytic activity of inorganic sunscreens is proposed. INTRODUCTION Solar creams and gels make wide use of sunscreen agents with the aim of protecting the skin from solar UV radiation exposure. Sunscreens act via absorption of UV radiation, thus lowering the radiation flux reaching the skin. Among these compounds, white inorganic pigments such as titanium dioxide and zinc oxide are widely used for their photostability and relevant absorption in the UV region (1). However, an important drawback connected with the use of these pigments is their being semiconductor oxides, thus showing photocatalytic activity upon radiation absorption. This means that semi- Address all correspondence to M. Eugenia Carlotti. 513