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How Hair Grows

The 3 Stages of Hair Growth

The growth and shedding cycle of the hair follicle is divided into three distinct phases. These phases are known as anagen (the growing phase), catagen (the intermediate phase) and telogen (the shedding or resting phase).

Hair begins appearing on the human body while it is still in the womb. By the time a developing fetus reaches 22 weeks old, there are already 5 million follicles on the body. Interestingly enough, that is all of the follicles that will ever develop regardless of how long we live. None will ever be added.

How Hair Grows
Scalp hair grows at an average rate of six inches per year, or only 0.3 0.4 mm per day. There are three distinct stages of hair growth.

A: Anagen Phase
This phase defines a period of activity where the hair cells are dividing and new hair growth occurs. Approximately 80% of your hair is in the anagen phase, and can grow for as long as two to six years. Shorter growth periods are indicative of people who have trouble growing their hair long.

In the anagen phase the cells at the base of the hair follicle divide and form the new hair which is then pushed up to the surface of the skin. The new hair pushes the old hair called a club hair out of the body. Once the hair has been completely formed the cells at the base of the follicle stop dividing and the hair stops growing. The hair then moves into the catagen stage where it is still nourished and remains firmly attached.

C: Catagen Phase
This transitional phase runs about two to three weeks. At any given time approximately 3% of your hair is in this phase. There is no hair growth during this period while the outer portion of the hair root sheath shrinks and attaches itself to the root of the hair.

T: Telogen Phase
This phase, known as the “resting period” is experienced by approximately 10-15% of your hair. Telogen lasts for approximately 100 days for scalp hair and significantly longer for other body hair. The hair follicle is completely at rest during this phase as well as the club hair being formed. The normal 50-100 hairs we see falling out daily are telogen hairs.

Finally, the hair moves into the telogen stage where the follicle no longer nourishes the hair and therefore the hair is shed. The follicle remains dormant for a certain period of time before the cycle is repeated.

This, in addition to the fact that hair follicle growth is not synchronized and therefore different hair follicles, depending on where the hair follicle is on the body causes the length of each of these growth stages to vary. The follicles on the scalp remain in the anagen stage the longest time and therefore the hair on the head grows the longest. When we are younger, the anagen or growing phase is longer, which is one of the reasons why we see young girls and boys with longer, healthier hair.

See Also:
Intro to Hair Loss
Hair Loss, Self-Image, & Society
Hair Anatomy
How Hair Grows
How Hair is Lost
Hair Loss in Women
Traction Alopecia
Hair Loss in Men
Norwood Hair Loss Chart
Frontal Hair Loss
How to Stop Hair Loss