Strategies for Skin Penetration Enhancement

Dermatological and cosmetic preparations frequently contain active principles which can only act when they penetrate at least the outermost layer of the skin. However, the efficacy of topically applied actives is often suboptimal because the transport into the skin is slow due to the resistance of the outermost layer of the skin, the stratum corneum. Most small water-soluble nonelectrolytes therefore diffuse into the systemic circulation a thousand times more rapidly when the horny layer is absent. Thus, a variety of means have been studied in attempts to overcome this barrier. Such strategies include physical, biochemical, and chemical methods (Figure 1).