The Hair Growth Cycle

The hair growth cycle consists of three stages:

1. Growth (Anagen)
2. Transition (Catagen)
3. Resting (Telogen)

During the Anagen or growth phase, the cells in the root of the hair are dividing rapidly, extending the hair shaft, with approximately 1cm of growth every 28 days. The matrix of the hair surrounds the dermal papilla which nourishes the hair during its’ stage of growth. It is at this stage that the hair is most receptive to laser as it is rich in protein, keratinized cells and melanin. The amount of time the hair follicle stays in the Anagen phase is genetically determined. A hair’s Anagen phase can last for several years, with Anagen hairs representing 85% of our body’s hair. At the end of the Anagen phase a biological signal causes the follicle to enter the Catagen phase.

During the Catagen or transition phase, chemical and structural changes occur in the follicle resulting in the hair retracting and drifting away from the dermal papilla. The hair stops growing, and remains in this phase for only two to three weeks before moving into the next phase. Approximately 3 to 4% of our body’s hair is in the Catagen phase at any given time.

During the Telogen or resting phase, the hair begins to shed while the follicle is stimulated to begin a new cycle. The length of this stage varies, and in some cases the hair is replaced immediately as a newly growing hair pushes the “resting” hair out of the follicle. The new hair emerges from the same opening at the surface of the skin as the old one, repeating the hair growth cycle again. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. Approximately 10 to 13% of our body’s hair is in the Telogen phase with 25-100 Telogen hairs being shed each day.