The Rheological and Skin Sensory Properties of Cosmetic Emulsions: Influence of Thickening Agents.

Hydrophilic polymers are widely used in the cosmetics industry as thickening agents/rheology modifiers. These thickening agents have different chemical structures which affect the rheological properties, as well as the sensory attributes of the formula. Systematic study is important to determine the relationship among them. Six commonly used hydrophilic polymers, including cellulose derivatives and synthetic polymers, were used as thickening agents in a series of oil-in-water emulsions. The rheological properties were evaluated in relation to the thickening mechanism and polymer structures. Comprehensive skin sensory studies were carried out to test factors such as the pick-up, rub-in, and after-feel of these emulsions and the control sample. Results showed that all the samples demonstrated a non-Newtonian and shear-thinning behavior, and synthetic polymer-based formulas were more viscous than cellulose derivative-based ones. All eight attributes for the factors of appearance, pick-up, and rub-in showed statistically significant differences ( p ≤ 0.05), whereas all five attributes for the after-feel factor exhibited no statistically significant differences ( p > 0.05) for different thickening agents. According to the results calculated using Pearson's correlation coefficients, four sensory attributes were mostly correlated with the rheological parameters.