Approximately five million hair follicles cover the human’s entire body. Though the hair varies from super fine to almost dark and thick structure, almost the entire body except the sole of the feet, the palms of the hand, and the lips are hairless. Unlike many animals whose hair growth varies according to weather or seasonal changes, human hair naturally goes through the three hair growth phases namely the anagen phase, catagen, and finally the telogen phase.
Almost 80 to 90 percent of human hair is in the anagen phase. During this phase, the hair is actively growing to about one centimeter in every 28 days. Scalp hair remains in this phase about more than two years to as much as six to eight years. The amount of time the hair spends in this phase determines the amount of length the hair will grow. Hair follicles in other parts of the body may only stay in this phase for just few months. This explains why scalp hair grows longer while other body hair stops growing at a certain length and point of time.
After the anagen phase, hair goes through the catagen phase where active hair stops growing due to major cell death. Usually, this phase last only from one to three weeks. Near the end of this phase, dermal papilla moves to give way to re-growth where the body produces new hair.
Telogen is the phase where almost ten percent of the hair is at rest. Lasting about two to three months, the hair will generally shed at this stage. On the average, about 50 to 100 hairs are shed everyday. The shed hair from the scalp usually reveals a white thing that is mostly dry and hard at the root, but extensive examination shows that the root is usually undamaged. After this resting phase, the growth phase will return.
Every hair undergoes the hair growth phases at one specific time or another. However, due to certain factors such as genes, hormones, and outside environment, the amount of time the hair stays to these hair growth phases may vary from time to time thus also affecting the results for each person such as hair loss for some.