Increased skin permeability for lipophilic molecules.

Treatment of the epidermis with surfactants can markedly increase the transport of polar molecules but only marginally increases the transport of nonpolar (lipophilic) molecules. Thus, other vehicle systems are needed to increase the transport of lipophilic molecules. One method to accomplish this increased transport is to add small quantities of polar lipids to a base vehicle containing propylene glycol. The transport of nonpolar materials such as salicylic acid can be increased by an order of magnitude by the addition of small amounts of fatty acids or alcohols to a formulation. The effect of this mixed system is much greater than the effect of any of the agents alone.