Photostability assessment of sunscreens. Benzylidene camphor and dibenzoylmethane derivatives

Abstract

Synopsis A rapid method has been developed in order to compare the photostability of several sunscreen agents incorporated in the same type of emulsion. Thin films of the different preparations were spread on quartz plates and irradiated with a solar simulator. Differences in energy distribution according to wavelengths observed with solar simulator and sun radiation were taken into account. A kinetic study of absorption properties was carried out under solar simulator irradiation. A simple calculation gave the results which would be obtained under sunlight. This technique differentiated the reversible transformations of photoisomerizable compounds from an irreversible disappearance which resulted in a significant loss of protective power. Applied to benzylidene camphor derivatives, this technique showed the excellent photostability of these sunscreen agents.

Combination of retinyl palmitate and UV-filters: Phototoxic risk assessment based on photostability and in vitro and in vivo phototoxicity assays

“…It is able to absorb UV photons and it has been shown to improve the photostability of sunscreen formulations containing the combination octyl methoxycinnamate/avobenzone (Chaudhuri et al, 2006). Photostability evaluation studies are usually performed using quantitative separation techniques as High Performance Liquid Chromatography (HPLC) Deflandre and Lang, 1988;Berset et al, 1996).…”

Complexation of the sunscreen agent, 4-methylbenzylidene camphor with cyclodextrins: Effect on photostability and human stratum corneum penetration

“…4-MBC is classified as an UV-B filter since it absorbs most efficiently in the 290-320 nm range and it is included in the list of authorized UV filters in Europe, Australia and is being considered for use in the USA [10]. Although 4-MBC has been regarded as rather photostable [6,11], recent studies have demonstrated that this sunscreen agent undergoes marked degradation under sunlight exposure [12,13]. Therefore, new systems with enhanced 4-MBC photostability are required.…”

Rationale for sunscreen development

“…The suitable filter was worked out based on extensive photochemical investigations to identify the structural requirements for optimal absorption and relaxation of absorbed quantum energy. 17,21,22,26 Terephthalylidene dicamphor sulfonic acid (Mexoryl SX, [Chimex SA, France] USAN: ecamsule) 25 containing either 2% avobenzone (A) or 2% avobenzone and 10% octocrylene (B) were spread on roughened quartz plates and exposed to 30 J/cm 2 ultraviolet-A. After exposure, films were solubilized in ethanol and residual content of avobenzone was determined by high-performance liquid chromatography.…”

“…This has permitted assessment of the stability of the protection level over time under UV exposure. 17 A solar simulator that sends out a light mimicking sunlight was used and equipped to expose sunscreen preparations to solar UVR spectrum. The light transmitted through the irradiated sample was analyzed and the amount measured throughout the trial.…”

“…However, they undergo significant degradation under UV exposure and this leads to a rapid decrease in their protective efficacy. [17][18][19][20] Extensive research on the photochemistry of filters 21,22 has led both to the identification of some potent photostabilizers of dibenzoylmethanes 23,24 and to the achievement of new UVA filters that have a highly photostable molecular structure. 25 An in vitro method has been developed to test the behavior of sunscreen products, ie, filters in the final preparation or vehicle.…”