How can the poor photostability of avobenzone in sunscreens be improved?

Avobenzone is one of the most widely used UVA filters in a majority of sunscreen formulations. It is widely used in sunscreen products due to its excellent protection against long-wave UVA radiation and its affordability. However, a major drawback of avobenzone is its photostability; it undergoes photoisomerization and photodegradation under sunlight. Furthermore, the photodegradation products of avobenzone can cause harmful side effects on the skin, including oxidative damage caused by free radicals. The following approaches exist to improve this problem:

Method 1: Preparation of a supramolecular Avo-glycerol sunscreen form

Avobenzone, ferulic acid, and ergothioneine are linked together to construct a supramolecular Avobenzone-ferulic acid-ergothioneine (AVB-FA-EGT) compound. This supramolecular AVB-FA-EGT exhibits enhanced broad-spectrum UV protection, photostability (up to 8 hours), and sun protection efficacy (SPF increased by 15.93 times). In addition, this supramolecular AVB-FA-EGT also possesses strong antioxidant properties, good biocompatibility, extremely low permeability, and excellent safety.

Method 2: Use Avo-glycerol instead of Avobenzone

Avobenzone was derivatized to avo-glycerol by replacing the p-methoxy group with glycerol at the ortho position. Avo-glycerol exhibited absorption in the UVA range (315–400 nm), similar to avobenzone, indicating good UVA coverage. Unlike avobenzone, a solution of avo-glycerol in an aprotic solvent demonstrates remarkable photostability, with no significant decrease in absorbance at the UVA range after 6 h irradiation. This suggests that the hydroxyl group in avo-glycerol functions as an efficient acid-base catalyst in enolization. Consequently, the rapid enolization of the photochemically generated keto form prevents its accumulation. This inherent photostability of avo-glycerol eliminates the need for photo stabilizers in sunscreen formulations and provides greater flexibility in selecting other sunscreen Components.

Method 3: Adding a Quencher

A photostable study using different concentrations of methoxyethylhexylpropylene (SolaStay® S1 quencher) in combination with avobenzone revealed that avobenzone exhibits good photostable stability at specific quencher concentrations. Compared to formulation F0 without the quencher, the effect of adding the quencher was significant, with a relatively smaller decrease in the photodegradation rate. Furthermore, formulation FSOL1, with 3% SolaStay®, was the best formula for SPF 45 sunscreen among all formulations. Photodegradation results were minimal in each experiment, with very low impact on the skin.

Reference:

[1] LU B, RUAN B, ZHANG J, et al. Supramolecular avobenzone sunscreen: a promising method for enhancing UV protection and photostability[J]. Journal of Materials Chemistry B, 2025, 47: 15362-15371. DOI:10.1039/D5TB01899D.

[2] SANG HEE LEE & Kyung K L. A highly photostable UVA filter derived from avobenzone[J]. Journal of Photochemistry and Photobiology A-chemistry, 2024, 458: Article 115972. DOI:10.1016/j.jphotochem.2024.115972.

[3] PUTRI WULANDARI; Vivin F S; Siltiwi Mandar. Photostability Study of Avobenzone in Commercial Sunscreen SPF 45 with Additional SolaStay® Quencher Upon Sun Exposure[J]. International Journal of Science and Healthcare Research, 2023, 48 1. DOI:10.52403/ijshr.20230248.

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