Hair follicles grow in repeated cycles. Each cycle consists of three phases and passes through the phases independent of the neighboring hair.
ANAGEN PHASE – GROWTH PHASE
Approximately 85% of all hair are in the growing phase at any one time. The Anagen Phase can vary from two to six years. Hair grows approximately 12-15 cm per year and any individual hair is unlikely to grow more than one meter long.
CATAGEN PHASE – TRANSITIONAL PHASE
At the end of the Anagen Phase, the hair enters into a Catagen Phase which lasts about one or two weeks. During the Catagen Phase the hair follicle shrinks to about 1/6 of the normal length. The lower part is destroyed and the dermal papilla breaks away.
TELOGEN PHASE – RESTING PHASE
The Telogen phase follows the Catagen phase and normally lasts about 5-6 weeks. During this time the hair does not grow but stays attached to the follicle while the dermal papilla stays in a resting phase below. Approximately 10-15 percent of all hair are in this phase at any one time.
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.