Introduction to Hair Health
Normal Cycle of Hair Growth and Loss
On average, there are 100,000 to 150,000 hairs on the human scalp. The hairs grow from hair roots, or follicles (saclike structures under the skin). Blood vessels at the base of each follicle provide the nourishment necessary for hair growth. Hair growth in each root occurs in a cycle independent of the other roots.
At any time, about 90 percent of the hairs on the scalp are in the growth phase, while the other 10 percent are in the resting phase. After 2 to 3 months, the resting hair falls out and new hair starts to grow in its place. This growing phase lasts for 2 to 5 years. Each hair grows approximately 1 centimeter per month during this phase. About 90 percent of the hair on your scalp is growing at any one time. It is normal to shed some hair each day as part of this cycle. On a typical day, about 50 to 150 scalp hairs are lost. Baldness (or alopecia) results when hair loss occurs at an abnormally high rate; when hair replacement occurs at an abnormally slow rate; or when normal hairs are replaced by thinner, shorter ones.