ABSTRACT
When focusing on drug delivery to regions in the skin such as the hair follicle, sweat and sebaceous glands, application of the drug on the skin surface has the potential to increase the drug concentration at the site of action and to limit the amount of drug in the systemic circulation. The rational of topical delivery may be of particular interest for skin diseases such as acne, cancer, and alopecia, which originate in the pilosebaeous unit (1-4), and also for cosmetic products to improve, e.g., the hair condition. This can be achieved by targeting active ingredients to the pilosebaceous unit. Local delivery can be improved by two approaches. The first approach is the selection of an appropriate formulation, which might contain particulate carriers and medium additives such as ethanol, surfactants, and propylene glycol. A second approach is the selection of a possible drug candidate. The physicochemical parameters of the drug, e.g., size, charge, and lipophilicity, can affect the degree of delivery and targeting. In those particular cases where formulation variation is not feasible, delivery and targeting can only be improved by the physicochemical parameters of the penetrant itself.
