People can see that their hair grows and falls out and that it’s the color that it is. But many don’t know exactly why. The secret lies in what happens in the hair follicle.

Hair is made out of keratin, which also makes up human nails and the claws, hoofs, scales and feathers of other animals. Each individual hair is made up of a root and a shaft. The root of the hair is a soft bulb, while the rest of the hair that grows up through the layers of skin and out is the shaft. The root and a bit of the shaft lie below the skin in a sac, and this sac is the follicle. A projection called the papilla lies at the bottom of the follicle. The papilla's a tiny projection that nourishes the hair root. The hair is lubricated by fat glands that produce a material called sebum. Muscles push against fat glands to help them lubricate the fat glands and are also responsible for making the hair stand on end when a person is frightened. 

Hair grows by forming new cells at the base of the follicle. As new cells form around the papilla, old cells are pushed up and die. Eventually, these dead cells are pushed up out of the follicle and become part of the hair shaft. In human beings, only one hair at a time grows from a follicle. The hair grows as long as the papilla provides nutrients to the new cells. In humans, the hair usually grows about a half an inch a month for between two and four years. The short hairs that are found on the eyebrows and eyelashes have a much shorter cycle, which keeps them from growing too long.

Usually when a hair shaft falls out, another hair replaces it. This cycle doesn’t happen to all the hair at the same time. People have between 90,000 and 150,000 hairs on their head and lose about 50 to 100 hairs a day. Because the other hair is growing or resting, this loss is not a cause for alarm. 

The color of a person’s hair comes from a pigment called melanin. Melanin is deposited in the cells as they form in the follicle and can produce hair that ranges from white blonde to blue black. As a human ages, the melanin sometimes isn’t deposited in the hair cells as it formerly had been, and the hair turns gray or white.