Hair Structure and Hair Life Cycle
Hair is composed of strong structural protein called keratin. Each strand of hair consists of three layers. An innermost layer or medulla which is only present in large thick hairs(I do not have that medulla as my hair is fine). The middle layer known as the cortex. The cortex provides strength and both the color and the texture of hair. The outermost layer is known as the cuticle. The cuticle is thin and colorless and serves as a protector of the cortex.
The structure of the Hair Root
Below the surface of the skin is the hair root, which is enclosed within a hair follicle. At the base of the hair follicle is the dermal papilla. The dermal papilla is fed by the bloodstream which carries nourishment to produce new hair.This is why exercise and scalp massages are so vital to hair growth because they increase blood flow(which carries nutrients) to the scalp.
Hair growth cycles
It takes a long period of two to six years for every hair strand on the scalp to attain its ultimate growth potential. During this lengthy growth period the hair is washed, conditioned, exposed to the heat and pollution, chemicals etc. None of these factors affect the normal growth of the hair follicles, but they can damage the hair shaft.
The phases of hair growth cycles
Hair growth goes through a cycle with three identified stages: Anagen (Growing Phase phase), Catagen (transitional phase), and Telogen (Resting phase). Approximately 90% to 95% of hairs are in the anagen phase, and 5% to 10% are in the telogen phase. In the scalp, the anagen growth phase lasts between 2 to 6 years, catagen between 2 to 3 weeks, and telogen between 2 to 3 months.
Anagen Growth Phase
In the anagen phase, hairs grow at a rate of about 0.5 inch per month which slows with age. Length of hair corresponds to the amount of time in the anagen phase. The length of the hair growth cycle is different for different parts of the body. This explains why hair on the head is longer than hair on other parts of the body, such as the eyebrows which only spend 30-45 days in the anagen phase.
Catagen Transition Phase
Catagen is the period of transition between the anagen growth phase and the telogen resting phase. Less than 1% of hairs are in this 2-3 week period at any one time. Changes take place in the structure of the hair follicle and at the end of catagen, telogen phase is entered. During the Catagen phase the hair follicle shrinks to about 1/6 of the normal length. The lower part is destroyed and the dermal papilla breaks away to rest below.
Telogen Resting Phase
Telogen is the resting phase of the hair growth cycle. At the end of the telogen phase, the hair follicles will reenter the anagen growing phase and start growing again. Approximately 5-10% of scalp hair is in the telogen phase at any one time and these follicles are randomly distributed. It is during telogen hairs that hair is normally shed. Approximately 50 to 100 hairs are shed each day.