Significance of the Follicular Pathway for Dermal Substance Penetration Quantified by Laser Doppler Flowmetry

In a study with 6 healthy male volunteers, the role of hair follicles in skin penetration was assessed by applying benzyl nicotinate to areas with open and occluded follicles and measuring blood flow with laser Doppler flowmetry. The results indicated that open follicles significantly increased blood flow and substance penetration, with a maximum blood flow of 7907 AU for open follicles compared to 3841 AU for closed ones. The time to reach maximum flow was shorter for open follicles (7.5-10 minutes) than for closed follicles (10-12.5 minutes), and the half-life of Vmax was also shorter for open follicles (9.9 minutes) compared to closed follicles (56.6 minutes). The area under the curve was significantly different between the two groups, suggesting that hair follicles significantly enhance the initial penetration of substances through the skin. This has implications for transdermal drug delivery, particularly for lipophilic drugs, and suggests that hair follicles could be targeted in novel drug delivery systems.