Photostability of Trolox in Water/Ethanol, Water, and Oramix CG 110 in the Absence and in the Presence of TiO2

Trolox (synthetic, hydrosoluble phenolic derivative of vitamin E, used as an active in cosmetic products) can undergo photooxidation upon UVB and UVA irradiation, the main degradation intermediate being Trolox C quinone. Trolox photodegradation rate decreases with decreasing polarity of the solvent, most likely because a more apolar environment inhibits oxidative processes. Ethanol is thus able to protect Trolox from degradation. Micellar solutions of Oramix CG 110® can incorporate Trolox in their core and protect it from photodegradation, either by providing an apolar environment or by competing for light absorption. Trolox can be degraded in the presence of titanium dioxide (an additive in many cosmetic products) under photocatalytic conditions, and both ethanol and Oramix show a certain protection effect towards Trolox photocatalytic degradation. However, concerning both direct photolysis and photocatalytic degradation, the protection given by ethanol and Oramix to Trolox results in at most 50% reduction of the transformation rate. Ethanol and Oramix (representative of the actual composition of cosmetic products) thus reduce but do not eliminate Trolox photodegradation. The solution to this problem might consist in the use of non‐transparent bottles for Trolox‐containing compounds and in the choice of titanium dioxide samples showing limited photocatalytic activity.