Flavonoid-enriched plant-extract-loaded emulsion: a novel phytocosmetic sunscreen formulation with antioxidant properties

The aim of this study was to develop a phytocosmetic sunscreen emulsion with antioxidant effect, containing a blend of flavonoid-enriched plant extracts. In vitro sun protection factor, antioxidant activity, skin irritation, photostability, cutaneous permeation, and retention of flavonoids were evaluated. Thermodynamically stable emulsions were obtained and tested for sensorial analysis after loading the blend of extracts. The selected emulsion was stable when stored at low temperatures (5 C), for which after 120 days the concentration of quercetin and rutin were above their limit of quantification, i.e., 2.8 ± 0.39 µg/mL and 30.39 ± 0.39 µg/mL, respectively. Spreadability, low rupture strength and adhesiveness were shown to be similar to a conventional topical product. Higher brittleness, pseudo-plastic, and viscoelastic behaviors were also recorded for the developed phytocosmetic sunscreen. The product presented a critical wavelength of 387.0 nm and ultraviolet rays A and B (UVA/UVB) rate of 0.78, confirming that the developed formulation shows capacity for UVA/UVB protection, protecting skin against damages caused by Ultraviolet (UV) radiation. Rutin was shown to permeate the skin barrier and was also quantified in the stratum corneum (3.27 ± 1.92 µg/mL) by tape stripping and retention test (114.68 ± 8.70 µg/mL). The developed flavonoid-enriched phytocosmetic was shown to be non-irritant to skin by an in vitro assay. Our results confirm the antioxidant activity, sun protection, and physical properties of the developed phytocosmetic for topical application. This research was funded by FAPESP (grant number 2015/25533‐7 and 2017/14757‐7), CAPES and CNPq. The authors also received support from the Portuguese Science and Technology Foundation (FCT/MCT) and from European Funds (PRODER/COMPETE) under the project reference M‐ERA‐NET/0004/2015‐PAIRED, co‐financed by FEDER, under the Partnership Agreement PT2020, and PhD scholarship (SFRH/BD/130555/2017).