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What Controls Hair Growth?

The body has a system of regulators, enzymes and proteins that lead to the generation of hair and control its growth. Each person has a hair growth cycle different from others, and this is why some people's hair can grow much longer than others. The body's own cycle is the only definite factor in controlling hair growth.

  1. Cell Growth

    • The hair follicles in your scalp contain stem cells -- one of the few places in the body where this is true. These stem cells migrate to the hair matrix and become matrix cells. It is here that the matrix cells divide and become different from one another; they become either hair cells or inner epithelial sheath cells. In addition, this is where hair develops its color. Amino acids produce pigments like melanin for dark color or pheomelanin for lighter color.

    Phases

    • Hair goes through three main phases of growth. The anagen phase is the first, and 85 to 90 percent of all hairs are currently in this phase. The anagen phase lasts two to six years, and is the time period that hair actually grows; the exact time period varies with each person and determines how long it can grow. The next phase is catagen, which is a two- to four-week period where the individual hair rests and does not grow while the follicle starts pushing out of the skin. That leads to the telogen phase, where the hair falls out and the follicle spends three to four months producing new hair. This is why it is natural to see hair falling out at any time.

    Main Factors

    • The follicle's stem cells gather in the outer root's base layer and form the matrix cells that can then become the hair cells. The dermal papilla's cells produce substances that determine whether the matrix cells become hair cells or sheath cells. The substances produced by the dermal papilla are determined by two factors. One is hormones. The other is the spinous layer cells along the outer root sheath. Proteins for basic fibroblast or platelet-derived growth factor can influence the production of enzymes that accelerate hair growth.

    Human Factor

    • Many theorize that a number of factors involving human behavior and habit can influence hair growth, but these have not been proven to be consistent with everyone. This includes stress, though studies at places like Humboldt University have suggested that stress can increase hair growth in some instances. Other factors frequently considered include nutrition and water intake.

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