SPF enhancement provided by rutin in a multifunctional sunscreen

Unprotected chronic exposure to solar radiation can contribute to premature skin cancer and sunscreens are a key factor to avoid those detrimental effects. Currently, there is a growing interest in the photoprotector and antioxidant potential of bioactive substances, such as rutin, that could increase the sun protection factor (SPF) value and, also, donate multifunctional characteristics to sunscreens. Recent in vitro findings indicated that rutin, when incorporated into sunscreens, can provide antioxidant activity and SPF improvement. However, clinical studies are fundamental to determine this activity, due to the lack of repeatability of in vitro methodology and low correlation with the in vivo data. We aimed at evaluating the clinical safety and in vivo SPF of rutin by comparing sunscreen formulations containing 0.1% (w/w) rutin, 3.0% (w/w) butyl methoxydibenzoylmethane and 8.0% (w/w) octyl dimethyl PABA (2-ethylhexyl 4-(dimethylamino)benzoato) with a similar bioactive-free preparation. Additionally, skin hydration, in vitro SPF and in vitro antioxidant activity of rutin, in association with the ultraviolet (UV) fillers, were investigated. The safety profile of the formulations under sun-exposed skin conditions qualified the formulas for clinical efficacy assays. 2,2-Diphenyl-1-picrylhydrazyl (DPPH) test confirmed the antioxidant properties of rutin, revealing around 40% increase in radical scavenging potential when the bioactive compound was present. Rutin in combination with the UV filters robustly elevated the clinical SPF around 70%, when compared with the bioactive-free formulation. To date, this is the first report in the specialized literature of an in vivo SPF measurement of a rutin-containing photoprotective preparation, supporting the claim that rutin is an effective and safe bioactive compound to be used in multifunctional sunscreens.