Hair growth is a cyclic and asynchronous process. Healthy hair undergoes three phases that re-occur in cycles.

In people with healthy hair about 85% of hairs are in the anagen, 1% in the catagen, and 14% in the telogen phases at any given time.

- The anagen or growth phase

Continous hair growth over 3-8 years

Telogen

During the anagen or growth phase, the matrix cells divide rapidly and move up the hair bulb where they become cells of the hair sheath and hair shaft, i.e. medulla, cortex and cuticle. The final differentiation of the cells takes place in the keratinizing zone. The process is concluded with the production of Keratin, the main component of the hair shaft, and the complete keratinization of the hair root cells. The anagen phase lasts between three and eight years.

Duration 2-3 weeks

- The catagen or transition phase

In the catagen or transition phase the division of the hair-forming cells gradually comes to an end. The hair bulb separates from the dermal papilla, and programmed cell death begins. The hair follicle shrinks to one third of its previous length and migrates towards the scalp surface. The catagen phase lasts 2 to 3 weeks.

Duration 2-4 months

- The telogen or resting phase

The hair falls out in the telogen or resting phase, either actively or passively as the newly growing hair pushes out the old. The follicle now moves deeper into the dermis and in the dermal papilla, until now reduced to a ball of cells, another anagen phase of new hair growth begins. The telogen phase lasts two to four months