In Vitro Photoprotection and Functional Photostability of Sunscreen Lipsticks Containing Inorganic Active Compounds

Abstract

Titanium dioxide (TiO2) is a safe inorganic ultraviolet (UV) filter with activity against UV damage. However, the recombination of the carrier’s charge and the tendency for TiO2 aggregation are the main disadvantages. Substrate supports, such as mesoporous silica, are biocompatible strategies to incorporate TiO2, altering its interaction with the skin. Since the lips are sensitive to the adversities of the environment, including UV radiation, the application of lipstick sunscreens is of great importance and expected to provide protection for this particular area against sunburn and photoaging, among other unfavorable responses unprotected UV exposure. We investigated the in vitro photoprotective efficacy and photostability of lipstick formulations containing TiO2 incorporated into mesoporous silica (SBA-15). The samples were the lipstick base; SBA-15; TiO2 (free form); and TiO2 incorporated into SBA-15. The photoprotective efficacy was characterized in vitro using a Labsphere UV2000S. Lipsticks were irradiated in a Suntest CPS+ chamber to evaluate functional photostability. Lipstick base and SBA-15 alone did not display photoprotective efficacy. The sample containing 10.0% TiO2 incorporated into the mesoporous silica generated greater photostability and sun protection factor (SPF) value compared to the one containing only 10.0% TiO2 (free state). Our findings suggest that TiO2 + SBA-15 can be considered a broad-spectrum ingredient for innovative sunscreens, particularly for the photoprotection of the lips.