Cosmetic dyes as potential photosensitizers of singlet oxygen generation

Photosensitizer molecules capable of absorbing UV radiation and visible light through photochemical reactions can generate singlet oxygen (O-1(2)). O-1(2) is an oxidizing agent that can react with biomolecules causing oxidative damage. Cosmetic dyes possess chromophore groups capable of performing the absorption process of electromagnetic radiation thereby they could act as photosensitizers. The aim of this research was to evaluate the photosensitizing ability of 25 dyes used as cosmetic ingredients through photo-oxidation of ergosterol as an indirect detection method of O-1(2). The presence of O-1(2) was indirectly detected by ergosterol conversion into ergosterol peroxide through H-1-NMR mixture analysis. Our results showed that 9 cosmetic dyes belonging to pyrene, chlorophyll, xanthene and aminoanthraquinone groups were able to act as photosensitizers in the generation of O-1(2). The photosensitizing ability of these dyes could be contradictory if they are used as cosmetic ingredients because of pro-oxidants effects caused by O-1(2) and its implications in skin photoaging. On the other hand, in regard to the photosensitizing ability of the remaining dyes tested belonging to the azo, triarylmethane, hydroxyanthraquinone, quinoline and indigoid groups, these were found not capable of photosensitizing O-1(2) generation, consequently their use as cosmetic ingredients wouldn't suppose an oxidation risk caused by O-1(2).