ABSTRACT
INTRODUCTION Exhibiting a protective barrier at the interface between the environment and the organism represents a major function of the skin (1), and especially of the stratum corneum, which is mainly composed of corneocytes and intercellular lipids. However, this skin barrier is not continuous but provides some weak points, such as the hair follicles, representing invaginations of the epidermis extending deep into the dermis (2). This is of special interest when discussing penetration of topically applied substances through the skin barrier. Next to intercellular penetration, the follicular penetration pathway has been shown to be of special relevance in this context (3-9). By extending deep into the dermis, the hair follicles provide an enormous actual area for potential absorption (2). The follicular reservoir was calculated to be as high as the estimated reservoir of the stratum corneum in some body regions (10).
