The growth cycle of the hair follicle. The cyclic activity of the hair follicle requires the regeneration and new assembly of its non-permanent portion during each new hair cycle. On average, the amount of new scalp hair formation matches the amount that is shed, thereby maintaining a consistent covering. Changes in hair growth cycling elicit a hair disorder. There are 3 main phases of the hair follicle cycle: an active growth phase called anagen; catagen when the hair follicle regresses; and telogen, when the hair follicle is largely quiescent. Two additional stages of the hair cycle have been described as; exogen (the release of telogen fibers from the hair follicles) and kenogen (the lag in time between the exogen and new anagen fiber development). The length of time each phase takes partly depends on the type of hair follicle involved and its geographic .