Allison Schaefer, Mariam Abou-Dahech,L aura Lam-Phaure, An Huynh, Katie Wolf, Mark Chandler and Gabriella Baki1
The University of Toledo, College of Pharmacy and Pharmaceutical Sciences, Department of Pharmacy Practice, 2 ACT Solutions Corp
Effect of emollients on the in vitro SPF and broad spectrum protection of organic UV filters
Sunscreens can be very effective in protecting the skin from ultraviolet (UV) radiation, a known carcinogen, when formulated properly. In new sunscreen products, a common goal is to maximize the sun protection factor (SFP) and have broad spectrum protection by using only small amounts of UV filters. Due to the recent ban in Hawaii, formulators have a quite limited selection of UV filters in the US, and the need for UVB and UVA protection boosting technologies is greater than ever. UV filters must be soluble in at least portion of the sunscreen formulation in order to be effective, therefore, solvent selection is critical. In this study, our goal was to understand how the in vitro SPF and UVA protection of selected organic UV filters and a combination of these UV filters can be boosted by emollients. First, 3 organic UV filters (homosalate, octyl salicylate and avobenzone) were selected and a literature research was done to identify emollients – marketed as solvents, solubilizers and/or photostabilizers for UV filters. From over 100 emollients, we selected 23 chemicals using Formulating for EfficacyTM (FFE). FEE matched UV filters and potential solvents and ranked solvents based on how successful they could be for our UV filters. Hansen Solubility Parameters, logP values, polarity, and additional physicochemical characteristics were obtained from FFE, literature and suppliers’ websites. Mixtures of UV filters and solvents were formulated, and in vitro SPF and broad spectrum protection (LabSphere, UV 2000S), and spreadability (TA.XTPlus texture analyzer) were tested. Our results indicate that in vitro SPF of organic sunscreens can be significantly enhanced through the use of emollients, and the chemical structure of solvents had a huge impact on the SPF boosting capability. Understanding the chemistry and interaction of UV filters and solvents can help formulators make more effective sunscreens.