Morphometric analysis of the human scalp hair follicle: practical implications for the hair transplant surgeon and hair regeneration studies.

[BACKGROUND] The bulge stem cell region is a structure important for the regeneration of the pilosebaceous unit. Measurements of the different compartments of a hair follicle may have implications in hair transplantation and hair regeneration studies.

[OBJECTIVE] To measure the length of the different portions of the occipital scalp hair and to estimate at what depth they are located.

[METHODS AND MATERIAL] Hair follicles from the occipital scalp were obtained from 29 individuals. Measurements were performed on digital pictures using a software imaging system. Antibody anticytokeratin (CK), 15 was used as a bulge stem cell marker.

[RESULTS] The mean length of a scalp hair follicle is 4.16 mm. The infundibulum measures 0.76 mm, the isthmus 0.89 mm, and the inferior portion 2.5 mm. The insertion of the arrector pili muscle is located 1.65 mm deep. CK15 immunoreactivity starts at a depth of 1 mm and extends down to 1.8 mm.

[CONCLUSION] The ideal depth for the trichophytic procedure is to cut the wound edge at a depth of less than 1 mm to avoid the bulge zone. The data provided can serve as an objective anatomical reference in hair regeneration studies using horizontally transected follicles.