Investigation of the penetration and storage of a shampoo formulation containing caffeine into the hair follicles by in vivo laser scanning microscopy

In the present study, the ability of a shampoo formulation containing caffeine as well as the fluorescent dye fluorescein to penetrate into hair follicles was investigated by in vivo laser scanning microscopy. A contact time of two minutes between the shampoo and the skin surface was sufficient for the formulation to penetrate deeply into the hair follicles and to remain there for up to 48 hours, even after washing. As hair follicles are surrounded by a close network of capillaries, dendritic cells and stem cells, they represent an important target for drug delivery. The results of the present study demonstrated that in vivo laser scanning microscopy is an efficient tool for the investigation of the dermatopharmacokinetics of topically applied molecules and their penetration pathways, as the method yields space- and time-resolved measurements.