The Growth Cycle of Hair

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Created on June 6, 2007

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Dr. Robert Jones

I get many questions regarding hair growth: Why am I shedding so much hair in the shower? Does my hair grow faster in the summer when I am out in the sun every day? These are common worries that are totally irrelevant to hair loss or the growth process of your hair. Hair growth is divided into three cycles – the Anagen, Catagen and Telogen phases. Hair will continually cycle through these three phases throughout a person's life. The cycle does not depend on the season or climate conditions, but does vary when a person has certain medical conditions, is taking medication or has another condition such as pregnancy.

Anagen is the growth phase of the hair. The hair in this stage grows rapidly at about 0.4 mm per day, 1 cm every 28 days. Scalp hair stays in this active phase of growth for two to six years.

Catagen is the transitional phase. About 3% of all hairs are in this phase at one time. The Catagen phase begins when growth finally stops, the hair is then released from the follicle, and is no longer attached at the root at the end of this stage. The detached hair in the follicle is called a "Club Hair".

Telogen is the resting phase and accounts for 6% to 8% of all hairs. This phase is essentially the shedding of the club hairs, and it lasts for different lengths of time on different parts of the body. On the head, this phase is about 100 days long. About 75 Telogen hairs are shed in a normal person each day.

Some people have trouble growing their hair long, and this phenomenon is genetic. Certain individuals have hair that spends more time in the Telogen phase and less time in the Anagen phase. To this extreme, arm and eyelash hair only grow to a very short length because their locations are programmed to provide a very short Anagen phase. These genetically determined differences between people are inalterable.

In the Anagen phase, quite interestingly, the same follicle planted on different parts of the body will grow to different lengths, showing that the growth cycle differs depending on where on the body the hair is growing. I have used chest hairs in various repair cases, transplanting these one-inch hairs onto the head. Amazingly, these hairs can grow up to three or four inches when planted on the head.

Developing a Mature Hairline

As males grow and mature from childhood through to adulthood, they experience a normal change in the hairline that is not a symptom of Male Pattern Baldness. At least once a week, I see a male in his early 20s who is convinced that he is losing all his hair. His hairline has receded about half an inch in the previous five years, and is slightly thinner than it was. As well, temporal angles have receded slightly. This change is part of the normal maturation process – it happens in every testosterone-producing male, and is not a sign that further balding will take place.