Photostabilization of butyl methoxydibenzoylmethane (Avobenzone) and ethylhexyl methoxycinnamate by bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), a new UV broadband filter

It is now well documented that chronic UVA exposure induces damage to human skin. Therefore, modern sunscreens should not only provide protection from both UVB and UVA radiation but also maintain this protection during the en tire period of exposure to the sun. UVA filters, however, are rare and not sufficiently photostable. We investigated the effect of the introduction of a new UV filter, bis-ethylhexyloxyphenol methoxyphenyl triazine (Tinosorb S), in oil in water sunscreen formulations on the photostability of butyl m ethoxydibenzoylmethane (Avobenzone [AVB]) after irradiation with an optical ly filtered Xenon arc source (UV irradiance adjusted at 1 mean effective do se [MED]/min). With spectrophotometrical methods to assess the sun protecti on factor (SPF) and UVA ratio and chromatographical methods to determine th e amount of UV filters recovered after irradiation we showed that Tinosorb S prevented the photodegradation of AVB in a concentration-dependent way, l eading to a sustained SPF and UVA ratio even after irradiation with doses o f up to 30 MED. Since AVB was shown to destabilize ethylhexyl methoxycinnam ate (EHM) we tested the effect of Tinosorb S in sunscreens containing this UV filter combination. Here too Tinosorb S showed photoprotective propertie s toward both UV filters. Thus, Tinosorb S can be used successfully to impr ove the photostability and efficiency of sunscreens containing AVB and EHM.