P1.6 the form of african american hair is programmed from the hair bulb: a functional and immunohistological study

S. Thibaut*, O. Gaillard*, P. Bouhanna+, B.A. Bernard*

*L’OREAL Recherche, Clichy, France +Paris, France

Few data on African hair follicles have been reported in the literature. In this study, we investigated African American hair growth and morphology.

Macroscopic study showed that, in contrast to the Caucasian type, the dermal implantation of African American hair follicles was curved. We observed that the bulb itself was bent, exhibiting a retro-version, and that the outer root sheath (ORS) was asymmetric along the follicle. We microdissected these follicles and cultured them in William’s E medium for eight days. Their in vitro growth was slightly lower than that of Caucasian follicles, about 0.25mm versus 0.30mm/day. More importantly, the curvature was maintained in the hair shaft newly formed in vitro.

We performed an immunohistochemical study to compare the structure and organization of a curly follicle to those of a straight follicle. We observed that the proliferative compartment of matrix cells was asymmetric: Ki67-labelled cells were more numerous on the convex side, exceeding the Auber’s line. Therefore, the follicle was bent and the different structures asymmetric. On the convex part of the follicle, the ORS was thinner, while the differentiation programs of hair shaft, cuticle and inner root sheath (IRS) were delayed, as revealed by hard keratin hHb2 and Transglutaminase-1 expression, respectively. Furthermore, alpha-smooth muscle actin protein (a-SMA), which is a tension marker, was expressed in the ORS on the concave side of the follicle, while the ORS of a straight hair was completely negative.

In the conclusion, the morphology of African American hair is programmed from the bulb.