Alkenones, a renewably sourced, biobased wax as an SPF booster for organic sunscreens

Abstract

Sun exposure can affect the skin in various ways leading to short- and long-term consequences. Waxes are often used to optimize the rheological behavior of products and provide an even sunscreen film on the skin, which can boost the sun protection factor (SPF) of ultraviolet (UV) filters. In this study, a biobased wax, alkenones, sourced from commercially available and sustainable microalgae was evaluated as an SPF booster in sunscreens. Thirty-five sunscreens were formulated using three waxes and four organic liquid UV filters. Products were tested for pH, viscosity, spreadability, stability, as well as in vitro SPF and water resistance. Alkenones' in vitro SPF boosting capacity was similar to beeswax and cetyl alcohol with three "reef-safe" UV filters. None of the waxes used provided significant water resistance, however, using film-former water resistance could be built into the products. A key finding is that alkenones increased the in vitro SPF without increasing apparent viscosity. All products had a skin-compatible pH and they all remained stable at 25 °C for 10 weeks. Overall, the alkenones' performance was comparable to those of the comparator waxes. Our in vitro results indicate that alkenones offer a sustainable, biobased, non-animal derived choice as an SPF booster for organic sunscreens.