Ask A Scientist
How does our body grow hair?
Asked by: Bryonna Sapp
School: West Middle School, Binghamton CSD
Teacher: Jo Ann Summerlee
Hobbies/Interests: Science, doing experiments in science class
Career Interest: Scientist
Answer from Michael Little
Distinguished Professor of Anthropology
Research area: Human adaptation to the environment Interests/hobbies: Swimming, choral singing, antique toys, books
We humans are mammals and, like nearly all mammals, we have hair or fur. Originally, mammals' hair was used to insulate the body to prevent the loss of heat in the cold. But now, in modern humans, hair mostly serves to decorate our bodies, but it may serve other functions as well. For example, hair on our head may cushion it and prevent the brain from overheating in the sun, while hair in our nose will filter out dust and other particles; and our eyelashes and eyebrows may protect our eyes.
In addition to those areas mentioned, adults have a lot of hair in their armpits, and men have beards. This kind of hair is called terminal hair, while the fine, short hair on much of the rest of the body is called vellus hair. We do not have any vellus hair on the palms of our hands, soles of our feet or our lips. As individuals get older, vellus hair on the arms, legs and chest (in men) will change to a darker and thicker terminal hair. Terminal hair comes in different colors such as light and dark brown, black, and various shades of red and blonde. Blonde and red hair is common in northern European peoples, but is also found in some African and Australian aboriginal peoples as well. We even have evidence that some Neanderthals had red hair.
Terminal and vellus hair grow in different ways. Basic hair follicles are found in the deep layer of the skin (the dermis), and follicles are the structures where hair shafts begin to grow. Hormones that are produced by our adrenal and other glands tend to regulate hair growth, its thickness and its color. Men tend to have more of the coarse terminal hair on their bodies, while women have more of the fine vellus hair on their bodies. Some hair will grow continuously, such as head hair, while other hair, particularly vellus hair, has a short growth period and then a period in which there is no growth. There is a continual loss of hair and growth of new hair over the head and body, but when people become older and then elderly, hair loss tends to be greater than the growth of new hair.
The evolution of hair in humans is a very interesting topic. We probably began showing a reduction in our body hair (or fur) several million years ago when we began hunting in a dry, hot, savanna land. Sweating, which is our primary means of getting rid of too much body heat, is more effective with bare skin than with a heavy hair covering on the body. Then when humans migrated into cool or cold areas, they invented clothing to keep them warm. As you can see, our skin and body hair and our culture are connected throughout our prehistory and evolution in very interesting ways.