ABSTRACT
The hair follicle is a unique structure, characteristic of mammals. It is also a fascinating organ, since it encompasses most of the rules which control body homeostasis, as well as cell and tissue integration into an organized, autonomous and self-renewing biological entity. Indeed, as will be seen later on, hair follicle-like skin-is composed of epithelial and dermal compartments, which interact with each other from the very beginning of its morphogenesis, as early as the third month of human embryogenesis, and throughout life. In the adult scalp, each of the 150,000 (estimated) follicles undergoes, on its own, a cyclical process of degradation and renewal which partly repeats the sequence of events which takes place during its formation during fetal life. Another fascinating feature of the hair follicle is its high degree of autonomy with respect to its dermal environment, since it is apparently able to drive its own androgen metabolism, its own inflammatory response, and maintain both structure and function, namely hair fibre production, when dissected out and kept under in vitro culture conditions.
