Effect of storage temperature on face serum stability

Abstract

Serum is a type of emulsion which consists of a number of immiscible liquids and solids which are thermodynamically unstable. Temperature is believed to be one of the factors to accelerate its instabilities. Considering the fact that temperature has indirect effects on emulsification, which could alter the interfacial tension thus change the viscosity. In order to prevent these kinds of instabilit ies, thickener and emulsifier are incorporated into the emulsion system to minimize the interfacial tension from coalescence and to act like a body to the system. Therefore, the present study aimed to evaluate topical face serum (o/w emulsion) differing its thickener and emulsifier mixture with respect to storage temperature. The thickeners used in this study were carbopol Ultrez 20 and xanthan gum while the emulsifiers used in this study were PEG 40 hydrogenated castor oil and glyceryl stearate. The formul ations were stored at 4 °C, 25 °C and 45 °C for a period of four weeks to investigate their stability. The parameters are colour, scent, phase separation, viscosity and pH. The results presented in this study showed good stability throughout the experimental period as there are no phase separations observed by centrifugal test. All formulations appeared as white and homogenous emulsions throughout the study. The pH of all samples are slightly acidic, which falls in the range of normal human skin, which are 4.8 to 5.8. The viscosities of the face serums were higher in low temperature and lower at high temperature as both viscosity and interfacial tension decrease with the increase in temperature. Thus, storage temperature should be tightly monitored to prevent quality degradation of the serum.