Effect of the addition of oxybenzone or octyl-methoxycinnamate on particlesize of submicron emulsions

The formulation of sunscreen products requires understanding of the solubil ization of these products in different vehicles to obtain aesthetic prepara tions and to evaluate long-term stability. For this study, two different ul traviolet (UV) filters were selected: oxybenzone (powder) and octyl-methoxy cinnamate (liquid). First the solubility of these UV filters was tested usi ng a three-component simplex-centroid design strategy. The mixtures were pr epared with three oily phases used in this field of cosmetics: liquid paraf fin, isopropyl myristate, and coconut oil. A phase diagram method was used to carry out a systematic study of submicron oil-in-water emulsions. Phase diagrams were produced by diluting fixed binary mixtures with water. The su rfactant consisted of polyoxyethylene-20-sorbitan monostearate/sorbitan mon ostearate (50/50, w/w). The oily phase contained equal quantities of each o il studied. From this water/surfactant/oil ternary system, we selected two reference emulsions with receptively 75/5/20 and 68/7/25 proportions. Photo n correlation spectroscopy (PCS) was used to investigate the influence of t hese two UV filters at several concentrations on droplet size and distribut ion of the oil droplets in the material. All emulsions were stored and chec ked every month for 6 months.