We asked a scientist who has lot's of hair and knows all about biology. Marisa Romano, email@example.com, gave us this answer.
Each hair is made of dead cells and it is rooted in a little pocket in the surface layers of the skin.
The root contains living cells which are constantly growing and dividing to add new cells to the hair. So the hair is always growing from its root.
The hair on our heads grows about 10 centimeters in a year however it hardly ever grows more than about 50 centimeters long because each hair grows for only about three to four years and then falls out after which a new one starts to grow.
All types of fur, including human hair, are subject to a cycle that can be divided into three phases: the anagen, or growth, phase; the catagen, or intermediate, phase; and the telogen, or resting, phase. In the anagen phase the papilla induces basal cells to begin development of a new hair. The new hair, growing both upward and downward, moves alongside the old hair and eventually pushes it out of the hair follicle. Hair growth stops in the catagen phase. Basal cells and the follicle migrate upward in the telogen phase.
Excerpted from Compton's Interactive Encyclopedia. Copyright (c) 1994, 1995, 1996 SoftKey Multimedia Inc. All Rights Reserved
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