7.4 Lesson 4: Hair Growth Cycle: Overview

Although the hair cycle is a dynamic, flowing process, the follicular life cycle can be divided into 4 phases, each with distinct metabolic processes: anagen, catagen, telogen and exogen.
There is also an additional latent phase called kenogen.
The anagen phase is the phase of active growth. This phase has 6 stages.
The catagen phase marks follicular regression.
The telogen phase represents a resting period.
The exogen phase occurs when the hair is shed (this has recently been included as a specific hair cycle phase, separate from telogen).
The kenogen phase is a latent stage where the follicle remains empty, dormant and inactive.
In the human scalp: the anagen phase lasts approximately 2-7 years, the catagen phase lasts approximately 1-3 weeks, the telogen phase lasts approximately 3-4 months, the exogen phase lasts approx. 1-3 days, and the kenogen phase lasts for approx. 1-5 months (longer in genetic hair loss).