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The hair cycle and male pattern baldness or androgenic alopecia (AGA) and female pattern baldness

Each hair has a lifespan: hair grows for a certain period of time, stops growing and then falls out. At the same time, a new hair grows from the same follicle (pore) pushing out the old hair. The new hair is initially thin and gradually grows thicker and fuller over time. Then, the hair comes to the end of its life and a new hair starts growing. This is the life cycle of a hair called as hair cycle.
Disruption of this hair cycle causes hair loss.

Transitional phase  Resting phase  Growth phase
Period when hair is formed and grows  Period when cell division in the hair matrix begins to stop and hair is not formed  Period when hair bulb begins to regress (apoptosis)  Period when cell division in the hair matrix completely stops

Source: New Hair Science
(Japan Hair Science Association)

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