Hair grows in repeated cycles, which can be broken down into three phases. Individual hairs pass through these phases independent of the neighbouring hairs. An average person will normally lose 100 to 150 hairs every day during the telogen phase of this cycle. These fallen hairs will then re-grow several months later once the follicle enters the anagen stage.
Anagen phase: |
This is the growing phase of the cycle. Anywhere from 85 - 90% of all hairs are in this growing phase at any one time. The Anagen or growth phase can vary from two to six years. Hairs in this stage will generally grow approximately 10cm per year. |
Catagen phase: |
At the end of the Anagen phase, the hairs enters into a Catagen phase, which is considered the transitional or breakdown phase. During the Catagen phase, which lasts for a few weeks, the hair follicle shrinks to about 1/6 of the normal length. The lower part is destroyed and the dermal papilla breaks away to rest below. |
Telogen phase: |
This is the dormant or resting phase. The follicle continues to shrink during this phase. This phase could last many weeks. The telogen, or resting phase follows the catagen phase. Approximately 10-15% of all hairs are in this phase at any one time. During this 5-6 week phase, the hair does not grow but stays attached to the follicle while the dermal papilla stays in a resting phase below. |
At the end of the Telogen phase, the hair follicle re-enters the Anagen phase. The dermal papilla and the base of the follicle join together again and a new hair begins to form. If the old hair has not already been shed the new hair pushes the old one out and the growth cycle starts all over again. In a person not experiencing hair loss, the number of hairs on the scalp remains relatively consistent due to the balanced nature of this growth cycle.
Once hair loss begins, the length of the anagen phase is reduced, while the length of the telogen phase increases. Hair becomes finer and less pigmented and doesn't grow more than a few centimeters during the anagen phase.
