The hair you can see is actually a string of dead keratin cells. The average adult head has about 100,000 to 150,000 hairs and loses up to 100 of them a day; finding a few stray hairs on your hairbrush is not necessarily cause for alarm.
At any one time, about 90% of the hair on a person's scalp is growing. Each follicle has its own life cycle that can be influenced by age, disease, and a wide variety of other factors. This life cycle is divided into three phases:
As people age, their rate of hair growth slows.
WebMD Medical Reference Reviewed by Stephanie S. Gardner, MD on October 13, 2017
American Society for Dermatologic Surgery.
American Academy of Family Physicians.