Functions of mixed emulsifiers and emulsifying waxes in dermatological lotions and creams

Structured and semisolid emulsions intended for application to the skin and mucus membranes (i.e. lotions and creams) are generally complex mixtures of excipients whose stability and bioavailability vary greatly. A knowledge of the physicochemical properties of such formulations is essential to optimize manufacturing conditions, provide cosmetic elegance and to optimize the delivery of the drug or cosmetic agent to the skin. This paper discusses the manner in which surfactants and fatty amphiphiles combined to form mixed emulsifiers and emulsifying waxes have the ability to (a) promote emulsification at the time of manufacture by the stabilization of oil droplets, (b) control stability during a shelf-life that can vary from days for extemporaneously prepared emulsions to months or years for commercial preparations and (c) control the rheological properties of the system by their interaction with water and other excipients in the external phase. The use of simple model systems to investigate these complex formulations is demonstrated. (C) 1997 Elsevier Science B.V.