Hair 101: The Science of Healthy Hair (2)

Hair growth begins in the skin in a hair follicle and has three phases:

1. Anagen Phase: The Growth Phase

The anagen phase is the longest phase in the cycle, lasting 2-6 years. In this phase, epidermal cells that form the root of the hair continually divide. As they divide, new cells push old cells out, producing the hair shaft. Cell division is facilitated by oxygen, energy and nutrients that are supplied through the bloodstream. For more information, see the post on what hair requires to grow.

About 90% of the hairs on a human head are in the anagen phase at any point in time. Each person has about 100 000 hairs on their head.

2. The Catagen Phase: The Destruction Phase

In this phase, the epidermal cells stop dividing and the production of the proteins found in the hair ceases.

3. The Telogen Phase: The Resting Phase

In this phase, the hair simply remains in the hair follicle but stops growing. The hair can easily be pulled out by washing and combing.

4. The Exogen Phase: The Shedding Phase

In one day, about 50-150 hairs are lost due to the exogen phase. Once the hair is shed, the anagen phase begins, and the cycle continues.

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Hair averages a growth rate of about 0.035cm a day, which is about 1cm a month. This means if a hair grows undisturbed through the anagen phase, it can be as long as 24-72cm.