The growth of human hair occurs everywhere on the body except for the soles of the feet, the inside of the mouth, the lips, the backs of the ears, the palms of the hands, some external genital areas, the navel, scar tissue, and, apart from eyelashes, the eyelids.
The protein called keratin makes up hair and stimulates hair growth.Hair follows a specific growth cycle with three distinct and concurrent phases: anagen, catagen, and telogen. Each phase has specific characteristics that determine the length of the hair.This hair will usually grow to several feet before terminating, but many humans develop much longer hair.
The three stages of hair growth are the anagen, catagen, and telogen phases. Each strand of hair on the human body is at its own stage of development. Once the cycle is complete, it restarts and a new strand of hair begins to form. The growth rate of hair varies from individual to individual depending on their age, genetic predisposition and countless environmental factors. It is commonly stated that hair grows about 1cm per month on average; however reality is more complex, since not all hair grows at once. Scalp hair is known to grow between 0.6cm and 3.36cm per month.The growth rate of scalp hair somewhat depends on age (hair tends to grow more slowly with age), sex, and ethnicity.
The anagen phase, known as the growth phase, is when the hair physically grows approximately 1 cm per month.It begins in the papilla and can last from three to five years.The span at which the hair remains in this stage of growth is determined by genetics. The longer the hair stays in the anagen phase, the longer it will grow. During this phase, cells neighboring the papilla in a germinative layer divide to produce new hair fibers.
The catagen phase, or the transitional phase, allows the follicle to renew itself (in a sense). During this time, which lasts about two weeks, the hair follicle shrinks due to disintegration and the papilla detaches and “rests,” cutting the hair strand off from its nourishing blood supply. Signals sent out by the body (that only selectively affect 1 percent of all hair of one’s body at any given time) determine when the on of melanin production in the hair bulb and apoptosis of follicular melanocytes. Ultimately, the follicle is 1/6 its original length, causing the hair shaft to be pushed upward.
During the telogen or resting phase (also known as shedding phase) the follicle remains dormant for one to four months. Ten to fifteen percent of the hairs on one’s head are in this phase of growth at any given time. In this phase, the epidermal cells lining the follicle channel continue to grow as normal and may accumulate around the base of the hair, temporarily anchoring it in place and preserving the hair for its natural purpose without taxing the body’s resources needed during the growth phase.
Add Comment