Life Cycle of Hair Growth
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Shedding
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The normal development of hair is a repeating cycle of growth, shedding, and regrowth. Most hair shafts will continue to grow for two to eight years in the anagen phase. A short catagen phase (about two to four weeks) follows, in which the hair follicle shrinks. In the next two to four months, the hair enters the telogen phase, in which the hair does not get any longer and may be pulled out easily with vigorous styling. About 10 to 15 percent of the hair on your scalp may be in this phase at any time. In the beginning of the next anagen phase, new hair growth begins and any older hair gets pushed up and out, if it has not already happened in the previous phase. Shedding between 100 and 200 hairs a day is considered normal. When using Propecia or Rogaine to promote new hair growth, it is common to have some shedding before the new hair reappears.
Graying
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At some point from your twenties onward, the cells in your hair roots that produce melanin (natural pigment in our hair and skin cells) may start to die. The color of hair may become gray, white, or even translucent. Because the growth cycles of individual hair follicles is so different, the graying may be very slow and uneven, or it may be fast and relatively uniform.
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Balding
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Diet, ethnicity and stress can hasten the process, but all of us will eventually experience some degree of baldness, whether a receding hairline, a bald spot, or hair thinning. Where the scalp is bald, the hair follicles remain in the telogen phase, and no new growth occurs. Treatments can stimulate bald areas to produce new hair, but they have to be maintained constantly, or new hair growth will stop again.
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