Formulation and characterization of sunscreen creams with synergistic efficacy on SPF by combination of UV filters

The objective of this study was to develop sunscreen cream formulations with high sun protection factor (SPF) and satisfied characteristics. The actives were anisotriazine (an organic UV filter) and titanium dioxide (an inorganic UV filter). Two optimal cream bases selected from several preliminary formulations were prepared and incorporated with both actives in the legislated concentrations via emulsification process. The samples were determined for in vitro SPF, physical appearance, pH, and viscosity. Moreover, the sunscreen creams were compared for SPF with those of their counterparts containing either anisotriazine or titanium dioxide at the identical concentrations. The stability was studied under freeze-thaw condition. The results indicated that synergistic efficacy on SPF of sunscreen combination was confirmed. The intrinsic properties of cream bases, especially viscosity, affected the SPF of the final products.