Rheological methods to characterize cosmetics

Rheological methods to characterize cosmetics are presented. Products examined include creams, lotions, and gels. These are plastic substances that exhibit non-Newtonian flow behavior. The onset of flow is product-specific and significantly different for lotions and creams. From the critical shear rate at the yield stress, the type of emulsion can be determined for both creams and lotions. Flow onset of a W/O emulsion occurs at a much lower shear rate than for an O/W emulsion. Gels have no characteristic yield stress but they can be distinguished by a critical sheer rate. The recovery time following strain at a stress below the yield stress is not a product-specific characteristic of creams, lotions or gels; however, it can be very significant with respect to reproducibility of measurement results.