Hair is made in tiny pouches in the skin called hair follicles. Each scalp hair has a normal 'life cycle'.
Most scalp hairs last about three years and grow about 1 cm a month. After a period of time (about three years), each hair on the scalp comes to the end of its life and falls out. The hair follicle rests for a short while. It then starts to make a new hair. All the hairs on the scalp are at different stages in their life cycle.
At any one time about 1 in 100 scalp hairs are at the end of their life ready to fall out. This is why you will commonly find a few hairs on your shoulders, and some hairs fall out each time you wash your hair.
The Normal Life Cycle of Hair :
In order to understand and correct hair disorders, it is necessary to fully understand the requlation systems of hair growth.
Hair grows from the papilla in different phases that involves the cyclic activity of the hair follicle.
The cycle includes three phases: growth, resting and shedding, called the anagen, catagen and telogen phases. At any given time, a random number of hairs will be in one of three stages of growth, resting and shedding: anagen, catagen, and telogen.
1.The Anagen Phase:
This stage is also called growth stage. In fact, hair in that stage grow about 1 cm per month. Depending on the person’s age and genetics reasons, a strand of hair might grow for up to 5 years..
In a normal hair scalp, 80-85% of the hair follicles are in anagen phase .Hair is produced by hair bulb cells through cellular activity. Anagen phase is characterized by intense mitotic activity ( cellular activity) in the hair bulb. During anagen stage, the size of hair bulb increases, mitotic activity is intense in the matrix and the first signs of differentiation of the hair appear. A new hair is formed and pushes the club hair (a hair that has stopped growing or is no longer in the anagen phase) up the follicle and eventually out. This results in new and dense hair growth.
2. The Catagen Phase:
After growing for up to 5 years, a hair guits growing and goes into a resting phase that lasts about 3 weeks. The cells become keratinized, mitotic activity stops, the follicle no longer produces hair.
3. The Telogen Phase:
Telogen is the shedding phase. In normal hair scalp, 14% of the hair follicles are in telogen phase. This phase lasts for about 90 days for scalp hair. During this phase, hair falls out of the follicle and the hairs are then replaced by the body. The cycle then repeats. Up to 100 scalp hairs per day may fall out.
It may happen that at the end of the telogen phase, the hair follicle does not enter the anagen phase or forms smaller, finer, colorless hair: this is the onset of alopecia.
Causes of Alopecia: