Quantitation of Penetrant Molecules Within the Skin

Many skin-care products—such as deodorants, moisturizing creams, after-sun lotions, and antiaging creams—lie in the borderline area between cosmetics and pharmaceuticals. Such products are frequently termed cosmeceutics. Skin-care cosmeceutics have been formulated with penetrants such as vitamin E, vitamin E lineolate, and retinoic acid. By far the most convenient in vivo technique for evaluating penetrant localization in human stratum corneum is to physically detach this layer with repeated applications of adhesive tape. The protocol involves the topical application of the penetrant formulation to the application site for a set exposure period, after which the excess formulation is washed off. For over two decades, the combined use of tape stripping and mechanical sectioning has been employed in order to study the in vivo penetration kinetics of several different agents through human skin. Until several years ago, the use of autoradiography in transdermal research was limited to qualitative analysis as a supplement to mechanical sectioning.