The hair growth cycle
Anagen (growth) Anagen is the period of active cell division and noticeable hair growth. Throughout hair cycling, about 90% of all follicles are in the anagen phase and can remain in this phase anywhere from 2 to 8 years.
Catagen (regression) Over 2 to 3 weeks, cell production is halted, and the hair follicle shrinks. The hair shaft begins to separate from the bottom of the follicle and forms what is referred to as club hair.
Telogen (resting) Derived from the Greek telo meaning end and gen meaning produce, telogen is marked as the end of hair production as the follicle undergoes dormancy or cell quiescence. The follicle can remain dormant for up to 3 months with the hair club intact.
Exogen (shedding) Coupled with the telogen phase, exogen is when the hairs fall out of the follicle, during which new hair begins to grow in the follicle as it returns to the anagen phase.