ABSTRACT
Introduction .................................................................................................................................... 361 Nature and Structure of Skin.......................................................................................................... 362 Physicochemical Determinants ...................................................................................................... 363 Reducing Skin Absorption — Possibilities .................................................................................... 364 Effects of Chemical Structure ......................................................................................................... 364 Formulation Effects......................................................................................................................... 367 Conclusions .................................................................................................................................... 368 References....................................................................................................................................... 369
The skin is constantly subjected to a barrage of chemicals and generally it acts as an extremely effective barrier. It prevents the ingress of xenobiotics and also stops us from losing excessive water. The reasons for this excellent barrier will be reviewed since if these are understood it is possible to identify how the permeability of the barrier can be altered. A consideration of the extensive literature on the subject reveals that most research has been conducted on ways of reducing the barrier properties of the stratum corneum. This is to permit better access of therapeutic agents both for local (topical) effect and for systemic (transdermal) effect. Formulation approaches are often employed in which penetration enhancers are used. Publications on retarding penetration are far from common. Perhaps this is an oversight since there are a number of reasons why it is desirable to retard permeation.
