Development and photoprotective effect of a sunscreen containing the antioxidants Spirulina and dimethylmethoxy chromanol on sun-induced skin damage

The literature claims that incorporation of antioxidants into sunscreens provides additional skin photoprotection by scavenging free radicals formed due to sun radiation, but there are limited in vivo studies that support this hypothesis. This study aims to examine whether addition of antioxidants to a broad-spectrum sunscreen increases its photoprotective effect in real-use conditions. Sunscreen formulations composed of stable UV filters (Tinosorb® S, Tinosorb® M, Uvinul® APlus, and Uvinul® T150) alone or in combination with antioxidants (Spirulina and dimethylmethoxy chromanol-loaded solid lipid nanoparticles) were developed and their appearance, odor, rheological behavior, Sun Protection Factor (SPF), and UVA protection were analyzed. Next, it was conducted a 3-month, single-blind clinical study with 44 healthy subjects (30-50 years). Before and 28, 54, and 84 days after twice-daily self application of the sunscreens on the face, the stratum corneum water content, transepidermal water loss, dermis echogenicity, and skin elasticity and pigmentation were measured. At the end of the study period, the volunteers answered a questionnaire containing terms related to sensory characteristics of the formulations. All formulations were stable and exhibited non-Newtonian and pseudoplastic behavior, in vivo SPF 30, and good UVA protection. Antioxidant supplementation to the sunscreen formulation significantly improved the skin pigmentation, the collagen degradation on the dermis and thereby the skin net elasticity after 84 days of treatment compared to the sunscreen alone. Concerning safety, all formulations were considered non-irritant according to the sensorial analyses, whose results agreed with the clinical study findings.

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