Hair Formation

Hair Formation

Hair formation begins in the third month of fetal life. Each hair grows in a follicle, which is made from epidermal cells that grow down into the dermis. Hair is created by the multiplication of special cells at the follicle base. A hair develops as the epidermis thickens and cells begin to grow down into the dermis. This invading down-growth forms a cap over some of the connective tissue to create a papilla. Cells of this papilla multiply to form the hair. As these cells are pushed up the central canal of the hair shaft, and thus farther away from their source of nourishment, they become impregnated with the hard protein-- keratin. The cells of the papilla continue to multiply and are successively filled with keratin as the hair grows. Other cells of the papilla form an internal root sheath of keratanized cells. A sebaceous gland develops from cells of the newly formed root sheath. In a fully formed hair follicle, the hair lies within a two-layered hair shaft. The sebaceous gland oils the hair and a small erector muscle is able to make the hair stand on end.