What is the Hair Growth Cycle?

Our hair follicles undergo a lifelong cyclical transformation that allows hair strands to grow and shed with four distinct phases: anagen, catagen, telogen, and exogen.

Anagen Phase

Known as the “growth phase,” the anagen phase can last about 2-7 years and determines the hair’s length before it falls out. In this phase, cells in the hair follicle divide rapidly, producing a protein called keratin, and move upward to form the hair strand. Typically, 85-90% of hair follicles are in this growth phase at any given time.^1-3

Catagen Phase

Known as the “transition phase,” the catagen phase is short-lived, lasting only a few weeks. This phase is a brief transition period where the hair strand stops growing, and the follicle undergoes changes to prepare for the resting phase. This process creates a white node at the end of the hair that can be seen later when hair has fallen out. Usually, only about 1% of hair follicles are in this phase simultaneously.^2,4 

Telogen Phase

Known as the “resting phase,” the telogen phase typically lasts about 3 months. During this phase, the hair strand is fully formed and no longer able to grow, but remains anchored in the hair follicle. Typically, 10-15% of hair follicles are in this resting phase at any given time. Stressors can cause hair follicles to prematurely enter this phase, leading to more shedding than usual.²

Exogen Phase

Known as the “shedding phase,” the exogen phase is sometimes considered a final phase of telogen. This phase is when the hair strand finally sheds, marking the end of that hair growth cycle and, ideally, the beginning of a new one. Typically, a new hair strand has been quietly beginning its anagen phase below the old, and the old hair sheds as the new hair becomes big enough to push it out.^1,2 Since a portion of hair follicles are normally cycling through the exogen phase, it’s normal to see an average of 100 hairs shedding each day.

Hair follicles are micro-organs, and much like any other organ, they are directly and indirectly impacted by the interconnected systems in the body. Changes in any of these systems—whether triggered by stress, hormones, aging, lifestyle, nutrition, or metabolism—can affect the hair growth cycle. Imbalances in the body can signal the hair follicle to prematurely stop growing, resulting in a shortening of the growth phase, premature shedding, and delayed new growth. If enough hair prematurely enters the shedding phase without the normal balance of new growth, hair shedding above the normal rate can start to occur and visually appear as hair thinning.¹