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Hair Growth

Hair growth occurs in cycles consisting of three phases:

Anagen (growth phase):   This is the active phase of the hair. Each hair spends several years in this phase.  The cells in the root of the hair are dividing rapidly.  A new hair is formed and pushes the hair up the follicle and eventually out. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for 2-6 years. Some people have difficulty growing their hair beyond a certain length because they have a short active phase of growth.  On the other hand, people with very long hair have a long active phase of growth. The hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30-45 days explaining why they are so much shorter than scalp hair.

Catagen (transitional phase):   Over a few weeks, hair growth slows and the hair follicle shrinks.  The root bulb looks elongated from being pushed out of the follicle.

Telogen (resting phase):   The rest period for the follicle.  The current hair is shed and no new growth takes place for a period of time.  The old hair detaches from the hair follicle. A new hair begins the growth phase, pushing the old hair out.

Approximately 84% of scalp hairs are in the anagen phase, 1-2% are in the catagen phase, and 10-15% are in the telogen phase.