Singlet oxygen generation in the presence of titanium dioxide materials used as sunscreens in suntan lotions

The goal of this study was to test photoreactivity of commercially available suntan lotions and their components (mainly TiO2). Isolated water insoluble components containing titanium dioxide appeared almost non-active in the tests of 4-chlorophenol degradation, however a fast UV-light induced degradation of azur B and oxidation of α-terpinene to ascaridol in the presence of these materials was observed. The photoreactivity of suntan lotions and their components was compared to the photoactivity of phenalenone (an efficient 1O2 photosensitizer). The results have proven a relatively low efficiency of hydroxyl radicals formation, however significant rates of reactions involving singlet oxygen were observed in the presence of either the components of the cosmetics or the suntan lotions used as received. Moreover, an efficient photocurrent generation by photoelectrodes made of isolated TiO2 materials reflects their photoredox properties. Although singlet oxygen scavengers used as additives in suntan lotions might decrease the risk related to generation of this reactive oxygen species, producers of cosmetics containing titanium dioxide should consider testing TiO2 photoactivity in reference to 1O2 generation.