Skin permeation: the years of enlightenment.

Considerable advances in our understanding of the mechanisms by which drugs permeate the skin barrier have been made over the past 60 years. The key publications, which have influenced the field of skin permeation research are highlighted in the present review. The methodologies commonly employed for estimation of skin permeability are discussed as are the mechanisms proposed for skin permeation. The principal findings from the commonly employed in vitro and in vivo models are considered as well as the applications of enhancers and surfactants for optimization of skin delivery. As these studies presaged the emergence of transdermal drug delivery research in the 1970s, early approaches to model and predict dermal and transdermal absorption are also outlined. The published work on skin permeability in this period embodies the fundamental literature sources for consultation by scientists new to and currently engaged in transdermal drug delivery.