Hair growth occurs in cycles. Each complete cycle has three phases that are repeated over and over again throughout life. The three phases are Anagen, Catagen and Telogen.
During the Anagen phase or growth phase , new hair is produced. New cells are actively manufactured in the hair follicle. During this phase, hair cells are prouced faster than any other normal cell in the human body. The average growth of healthy scalp hair is about one half inch per  month. the rate of growth varies on different parts of the body, between sexes, and with age. Scalp hair grows faster on women than on men. Scalp hair grows rapidly between the ages of 15 and 30, but slows down sharply after the age of 50. key note about 90 percent of scalp hair is growing in the anagen phase at any one time. the anagen phase generaly lasts from three to five years, but in some cases it can last as long as 10 years . the longer the anagen cycle is the longer hair is able to grow. this is why some people can only grow hair down to their shoulders, while others can grow it down to the floor!

The Catagen phase is the brief transition period between the growth and resting phases of the hair follicle. it signals the end of the growth phase. During the catagen phase, the follicle canal shrinks and detaches from the dermal papilla. The hair bulb disappears and the shrunken root end forms a rounded vlub.less than 1 percent of scalp hair is in the catagen phase at any one time. The catagen phase is very short and lasts from 1 to 2 weeks.

The Telogen or resting phase is the final phase in the hair cycle and lasts until the fully grown hair is shed. The hair is either shed during the telogen phase or remains in place until the next anagen phase, when the new hair growing in pushes it out. About 10 percent of scalp hair is in the telogen phase at any one time. this phase lasts 3 to 6 months as soon as the phase ends the hair returns to the anagen phase and  the entire cycle repeats itself once every 4 to 5 years.

Postpartum Alopecia
is temporary hair loss experienced at the conclusion of a pregnancy. For some women, pregnancy seems to disrupt the normal growth cycle of hair, with very little normal hair loss during pregnancy, but sudden and excessive shedding from 3 to 9 months after delivery. Although this is usually very traumatic to the new mother, the growth cycle generally returns to normal within 1 year after the baby is delivered .