Hair is made up mostly of keratin, a protein also found in nails and skin. Each strand of hair on your body grows from a tiny, pouch-like structure in your skin called a follicle. The hair root in the follicle is alive. Blood vessels at the base of the follicle feed the root and keep it growing.
There are several types of hairs: terminal, vellus and intermediate hair. Terminal hairs are considered the regular hair. It grows after it is cut and has color and texture. Vellus hairs are found in the areas where there is hair loss. These hairs are thin, fine, soft in texture and lighter in color than terminal hair. Intermediate hairs are in between terminal hair and vellus hair. They are in transition and will in time produce a vellus hair.
The Life Cycle of Hair
The hairs on your head grow independently and continuously.
At any time, about 85% of the hairs on your head are in the growth phase and about 10% are in the resting phase. If a hair falls out before a new growth phase begins, the follicle is in a "hairless" resting phase (exogen). In some follicles, this phase can last up to 12 months.
The Process of Hair Loss
The anagen phase becomes gradually shorter and the hair follicle begins to shrink. These changes occur over the passing of several hair growth cycles. The reduction in the length of the anagen phase are what causes the terminal hair’s transition to an intermediate hair, and then eventually to a vellus hair.