Hair grows in a cyclical pattern. After hair is grown up, it falls off, and new hair comes out again. The periodical cycle of hair growth is called “hair cycle”. This is a strange and elaborate mechanism.
Hair is considered to be one of the organs in the body. There is no other organ like hair, that repeats the cycle of generation, regression, loss and regeneration.
Hair grows thicker and longer in the anagen phase. Then, hair stops growing and hair follicle becomes shorter in the following catagen phase. After the phase, hair follicle takes a rest in the telogen phase, which is followed by the exogen phase. Then, the next anagen phase begins, and new hair begins to grow.
Duration of the anagen phase of scalp hair is 3-5 years in men and 4-7 years in women. Females have longer anagen phase than males. Duration of the catagen phase is about 2-3 weeks, and the telogen phase is about 3-4 months. The exogen phase is about 2-3 months in length. Scalp hair repeats this hair cycle through the life.
Usually, about 90% of total scalp hair is in the anagen and catagen phases. About 10% of total hair is in the telogen and exogen phases.
In this way, new hair grows up, mature hair falls off, and the next hair grows again in a cyclical pattern. The hair growth cycle is a quite strange phenomenon.