Status of terpenes as skin penetration enhancers

Since its introduction, transdermal drug delivery has promised much but, in some respects has still to deliver on that initial promise, due to inherent limitations imposed by the percutaneous route. The greatest obstacle for transdermal delivery is the barrier property of the stratum corneum. Many approaches have been employed to breach the skin barrier, of which, the most widely used one is that of chemical penetration enhancers. Of the penetration enhancers, terpenes are arguably the most highly advanced and proven category and are classified as generally regarded as safe (GRAS) by the Food and Drug Administration. This paper presents an overview of the investigations on the feasibility and application of terpenes as sorption promoters for improved delivery of drugs through skin.