Research Summary
There are currently 14 organic and 2 inorganic UV filters approved in the United States. Due to coral reef safety concerns, octinoxate and oxybenzone have been banned in Hawaii, Key West, FL, and the US Virgin Islands. Additionally, octocrylene is being studied for its potential impact on coral reef safety, leaving 11 organic UV filters as viable options for sunscreen manufacturers, though there are limitations on their combination. Since consumers are always seeking sunscreens with high SPF and broad-spectrum protection, the need for UVB and UVA protection-boosting technologies is greater than ever.
In a preliminary study, about two dozen emollients were scanned for their SPF-boosting capability with selected organic UV filters. The goal of this study was to evaluate whether and to what extent the in vitro SPF and broad-spectrum protection of three selected organic UV filters (homosalate, octisalate, and avobenzone) and two inorganic UV filters (zinc oxide and titanium dioxide) could be boosted with three selected emollients (diethylhexyl 2,6-naphthalate, C12-15 alkyl benzoate, and butyloctyl salicylate), as well as an SPF-boosting ingredient (SunSpheres™).
Organic, inorganic, and mixed organic/inorganic sunscreens were formulated and tested for stability, viscosity, spreadability (using a TA.XTPlus texture analyzer), droplet size, in vitro SPF, broad-spectrum protection (using LabSphere 2000S), and water resistance. The results revealed that C12-15 alkyl benzoate provided the highest in vitro SPF among the three emollients tested for the organic sunscreens. However, this ingredient did not form a stable emulsion with the inorganic ingredients, leading to the selection of butyloctyl salicylate for this research project.
Titanium dioxide showed a higher in vitro SPF value, while zinc oxide provided broader spectrum protection. As a result, zinc oxide was chosen to be combined with the organic UV filters. An in vitro SPF increase was observed in all sunscreens after being exposed to a 20-minute water bath. It is believed that the film-former, polyamide-8, and the drying time contributed to the higher SPF values post-water bath.
All sunscreens exhibited shear-thinning behavior, which is typical for creams and lotions. Overall, the organic/inorganic UV filter-based sunscreen containing the SunSpheres™ (CS) performed the best in terms of in vitro SPF, water resistance, and spreadability.
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