Emulsions are the most commonly used skin delivery systems for active ingredients in cosmetic and pharmaceutical applications; as a consequence, they often receive less attention than they deserve from the point of skin delivery. Almost every component in an emulsion has the capability to influence the skin delivery of actives incorporated in the formula, but until recently this capability had not been fully realized to increase the efficacy of active ingredients.
This column will discuss ways in which ingredients can positively affect the partition coefficient of the active between the formula and the skin. By carefully selecting the emollients used in a formulation, formulators can increase the delivery and clinical efficacy of a formulation without increasing the level of the active ingredient. Examples will show that using this so-called “Formulating for Efficacy” formulation strategy can significantly enhance the clinical efficacy of a topically applied emulsion.
Emulsions are a technologically simple yet elegant skin delivery system. The feel, stability and delivery of an emulsion are determined by the combination of emollients and emulsifiers. The choice of the emollients determines the extent of skin delivery while the choice of the emulsifiers determines the rate of skin delivery. To explain these effects, some fundamental skin delivery theory may be useful.