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The Basics of Hair Growth

Each hair grows out of a hair follicle. The follicle does not sit on the top of the skin. The follicle is in a sebaceous gland, a tiny indentation in the skin. The process of hair growth begins in the follicle.

The human body contains two types of hairs. Most of the body is covered with vellus hairs. The scalp and the eyebrow both contain terminal hairs. This article will describe the process for hair growth in a terminal hair.

During a human's first year of life, all of the terminal hairs on his or her head grow at the same rate. After an infant becomes a toddler then different terminal hairs grow at different rates. Each hair on the toddler's head has a different growth cycle.

Hair growth requires the production of new cells. New hair cells are produced in the lower part of the hair bulb. The hair bulb is the part of the hair that remains inside of the hair follicle. While in the follicle, it is nourished by the blood that flows in the skin, the skin that cradles the hair bulb.
As new hair cells form, they push on the old cells, cells attached to the hair bulb. Pushed by the new cells, the older hair cells move up the hair bulb. Eventually, the pushed hair cells reach the top of the hair bulb. At that point they undergo an important change.

When the hair cells get to the top of the hair bulb, they begin to form 6 cylindrical layers. The cells in the inner layer will harden; they will contain the protein called keratin. The hardened cells in the inner layer are viewed as the strand of a human hair.

The rate at which new cells form in the hair bulb plays a large part in determining the rate at which any one hair will grow. The formation of new hair cells requires the division of precursor cells. As is always the case in cells growth, that division takes place faster, if the cells are well fed. That is why thinning hair can be prevented with the proper diet.

Hair growth also involves the production of keratin. Because keratin is a protein, its production is genetically controlled. That fact helps to explain why some people have faster growing hairs than other people.

Hair growth, like so many aspects of life, demonstrates both the effect of the environment and of the genetic component of the living cell.


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