In a sunscreen product, oil phase comprises of UV filters and emollients that modify spreadability or sensory and/or stabilize the UV filters. Because of the nature of UV filters, sunscreen products often contain a higher amount of oil phase than other types of skin care products. Hence, conventional surface-active agents (i.e. emulsifiers) are required to stabilize the system. The use of emulsifiers often leads to concerns over potential skin irritation as well as water resistant properties. Improved water resistance of wax or long-carbon-chain-based emulsifiers or water-in-oil emulsion system may cause an unpleasant after-feel on skin. On the other hand, with the limited selection of UV filters, formulators must rely on the stabilizer system to provide innovative textures or improve user experience. Therefore, it is vital to develop a formulation strategy which enables high performing sunscreen products free of conventional emulsifiers while addressing the unmet needs above at the same time.
Newly developed biopolymers (from cellulose derivatives and polysaccharides) have exhibited promising capabilities to stabilize and suspend oil droplets and particles. Synthetic polymers that can stabilize high oil loading oil-in-water systems help provide new texture options with a light and watery sensory. Moreover, formulations stabilized by polymers without conventional emulsifiers can exhibit good water resistance because such polymers have film formation properties and do not re-emulsify upon contact with water.
In this study, biopolymers (incl. cellulose gum, diutan gum, tara gum) were investigated, individually and in combination with synthetic polymers, for SPF 30 and SPF 50/50+ sunscreen systems. The UV filter systems selected were organic UV absorbers and hybrid UV filter systems, containing both organic UV absorbers and inorganic UV particulates (Titanium Dioxide and Zinc Oxide). A hydrophilic organic UV absorber (Phenylbenzimidazole Sulfonic Acid, PBSA) was deliberately chosen to test the electrolyte tolerance of the systems. Formulations prepared were subject to physicochemical analysis, microscopic analysis, stability tests, and in vitro SPF/UVAPF measurement.
Sunscreens targeting medium and high UV protection were successfully prepared with different textures and sensory profiles. Results show that there are synergies between polymers in thickening efficiency, stabilization, and suspension. Biopolymers displayed a high electrolyte tolerance and better compatibility with Zinc Oxide. The combinations of polymers provide a wide collection of differentiated textures while demonstrating robust formulation stability with an aesthetically pleasant sensation. In vitro SPF/UVAPF measurement confirmed the high performance of the emulsifier-free sunscreen systems.
Stabilizer systems for medium and high SPF systems are proposed with a mapping of textures and sensory profiles, and sample sunscreen formulations are given with in vitro SPF/UVAPF values as references, both of which can be extremely useful to formulators for developing effective and stable emulsifier-free sunscreen products.