Hair follicles continuously transition through phases of birth, death and rest as part of the natural hair-growth process. While follicles die temporarily, rebirth or regeneration also occurs. However, certain conditions -- such as baldness and skin trauma -- can cause hair follicles to die completely. As of 2010, no treatment exists to stimulate hair growth in follicles that completely die.
Hair follicles are sheath-like structures located in the skin. At the base of each follicle lies the dermal papilla, the blood-rich structure responsible for hair growth. Cells, called melanocytes and keratinocytes, line the walls of the lower follicle while the hair is actively growing. These cells reproduce and die, resulting in hair growth. Follicles also house sebaceous glands, which produce oil or sebum.
Hair growth occurs in phases of active growth, death and rest called the anagen, catagen and telogen phases. The anagen phase lasts approximately two to six years, during which hair grows 1 centimeter every four weeks. During the catagen phase, follicles undergo a cyclical, temporary death. During the telogen phase, the hair sheds.
During the catagen phase, hair follicles and the cells within them undergo a programmed cell death, according to Hair Biology. During this phase, the follicle regresses and protein and pigment cell production stops. The hair-growing structures die and wither away, and the follicle becomes more superficially rooted within the skin. While some cells are still present at the base of the follicle, synthesis does not occur, according to Hair Biology. The follicle is essentially dead. After a brief period of rest, however, the follicle enters the anagen phase and becomes active or alive once again.
Two factors can cause hair follicles to die permanently and completely: hereditary baldness and scarring. Hereditary baldness affects hair follicles, causing them to shrink and become more superficially rooted in the skin, according to MayoClinic.com.As the condition progresses, hair growth becomes finer and weaker. Eventually the follicle closes and dies completely, resulting in complete, permanent baldness. Scarring of the skin tissue may also permanently kill hair follicles, preventing further hair growth.
Scientists from the Department of Dermatology at Kligman Laboratories, University of Pennsylvania School of Medicine, have stimulated new follicle and hair growth in laboratory mice using a protein. Researchers hope the discovery could eventually help stimulate new hair growth in humans as well; the experiment has not yet moved beyond mice.