The skin has there layers: The outer layer, called epidermis, consists of epithelial cells. Under this lies the dermis consisting of connective tissue. At the bottom there is a layer called the hypodermis consisting mostly of fat cells.The skin has narrow pores, hair follicles, extending from the surface down to the top of the sub-dermis, called hair follicles. A hair extend from a growth zone in the bottom of each hair follicle and out at the skin surface.
By the common form of hair loss, a substance in the body, dihydroxy-testosterone (DHT), gives a signal to the cells in the hair follicles that make these cells divide less so that the production of hair slows or stops. DHT is a metabolic product from testosterone, the male sex hormone. Also women have some amount of testosterone and DHT in their body, and therefore hair loss also affects women.
Only cells that are susceptible to the influence from DHT will slow the growth process. This susceptibility is inherited from the parents by some individuals, and not by other. Follicle cells in the lower parts of the head are usually also resistant against the influence from DHT, and therefore these areas seldom get bald.The effectiveness of hair growth will not only be affected by DHT.
Other substances found in the tissue may give the cells signals to divide more, and nutrients like vitamins, minerals and essential fatty acids may make the growth process more effective. Some substances in the tissue may also block the DHT or ease the removal of this substance. Therefore all individuals susceptible to the influence of DHT will not lose hair in the same extent.