Morphometry of human terminal and vellus hair follicles

Previous studies suggest that drug delivery systems based on particles can be used to deposit active compounds in hair follicles and to target hair follicle-associated cell populations. The development of application protocols is complicated by the fact that there is no information available on the size and the position of key target structures in the different hair follicle types and their intra- and interindividual variation. Therefore, we performed morphometric measurements on histological sections of human terminal (THF) and vellus hair follicles (VHF) from the scalp and the retroauricular region. With 3864 +/- 605 mu m and 580 +/- 84 mu m in THF compared to 646 +/- 140 mu m and 225 +/- 34 mu m in VHF, the total length and the length of the infundibulum differed significantly as determined by paired t-test (P < 0.0001). The same level of significance was observed for the position and the length of the bulge region. The thickness of the epithelial lining was lowest in VHF (45 +/- 14 mu m at 100 mu m from skin surface) compared to 65 +/- 20 mu m at 150 mu m in THF, while the thickness of the interfollicular epidermis ranged between 64 +/- 12 mu m and 99 +/- 18 mu m in VHF-bearing skin and 72 +/- 16 mu m and 136 +/- 37 mu m in THF-bearing skin. In addition, the diameter of the hair follicle opening was determined at 50 mu m intervals from the skin surface. Our data suggest that hair follicle types in defined body regions represent rather homogenous groups and that particle-based drug delivery may be a feasible approach, also in larger numbers of individuals. We provide precise information on the size and the position of key target structures in VHF and THF.