Speaker: Dr. Myriam Sohn

Company: BASF Grenzach GmbH

Title: Photostability of Triazine-based UV filters

Language: German

Abstract: Cosmetic UV-filters based on 1,3,5-Triazine chemistry are largely used with 67% of sunscreens launched in Europe in 2022 containing at least one of them. Main representatives are the lipophilic Ethylhexyl Triazone (EHT) and Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine (BEMT) filters which need to be dissolved in cosmetic oils for use in sunscreens. Another example is Tris-Biphenyl Triazine (TBPT), which is prepared as an aqueous dispersion of particles due to its low solubility in water and oil.

These filters are generally regarded as the benchmark for photostability. To achieve the minimum requirement for UVA protection, a sunscreen also typically contains a UVA filter such as Butyl Methoxydibenzoylmethane (BMDBM) or Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB). Compared to DHHB, BMDBM shows poor photostability and can also impact the photostability of other filters present in the sunscreen.

To palliate its lack of stability during UV exposure, BEMT is often used together with BMDBM to quench its excited state and prevent its photodegradation. However, less is known about the consequence for BEMT in this process. Therefore, we examined the impact of BMDBM on the photokinetics of BEMT as well as on the other main 1,3,5-Triazine filters by experimental techniques and quantum-chemical calculations to identify possible photo-stabilizing or -destabilizing mechanisms within the binary systems. DHHB was evaluated as an alternative to BMDBM.

In the experiments, BMDBM showed a photodestabilization effect on the lipophilic 1,3,5-Triazine-based filters. In contrast, DHHB did not show any photodestabilizing effects, and even acted as a photostabilizer. The experimental observations were in accordance with the quantum-chemical calculations, which for instance, predicted a triplet-triplet energy transfer from triazines to DHHB. This study shows the usefulness to identify photostabilization / photodestabilization mechanisms between UV filters to best choose the UV filter combination for an efficient and safe sunscreen.