PHYSIOLOGY OF HAIR GROWTH

Abstract

Growth of hair is defined in terms of cycle of growth, rate of growth, and size of hair. Alteration of the normal cyclic pattern of growth accounts for hair loss associated with pregnancy, illness and some drugs. Inhibition of rate of growth accounts for hair loss due to mitotic depressant drugs such as those used in cancer chemotherapy. Suppression of mitotic generation of hair matrix cells permits compression of the matrix by surrounding tissues; a hair shaft with a zone of reduced calibre is thereby produced. Ensuing hair loss is due to breakage of hair rather than to its falling out by the roots. Increase in size of existing hair papilla accounts for the male beard at puberty and hirsutism in women. Change in hair size occurs in response to disease, drugs, or hormones.