Hair Follicle

Anatomy and Function

Hair follicles are found in the first and second layers of your skin (epidermis and dermis) and are present all over the body. They vary in size and shape depending on their cellular makeup. 

Hair follicles can degenerate and regenerate, allowing hair growth to occur in cycles. The cycle of hair growth includes three phases:

Anagen Phase

The first phase is the active phase of hair growth, in which the cells at the follicle’s root (dermal papilla) rapidly divide to form a new hair shaft. The shaft continues to grow and eventually pushes outward through the skin. The duration of the anagen phase depends on the location of the hair follicle and an individual’s age and overall health. The anagen phase can last anywhere from two to seven years for hair follicles located on the scalp. While the anagen phase for body hair usually lasts a few months. 

Catagen Phase

The second phase of hair growth serves as a transitional period. During this phase, hair growth stops, and the outer root sheath detaches from the follicle, cutting the hair strand from its blood supply and anchoring it to the skin. 

Telogen Phase

The third phase is the resting or shedding stage. During this period, the dermal papilla becomes inactive. The hair stops growing but remains anchored in the follicle. This period lasts approximately three to four months. Once the dermal papilla becomes active, a new hair shaft forms, pushing the old hair growth. 

 In addition to hair growth, hair follicles are responsible for healing the skin after injury and forming new blood vessels (angiogenesis) and neuron cells (neurogenesis).