Hair we see on the surface of our skin except on the head may actually seem unwanted. Actually, it play a big role in maintenance of the body. Human body is covered by finer and shorter hair. Most adults are found to have about 5 millions hairs across their bodies. The lips, palms and soles of feet do not carry any.
Every strand of hair grows from the cells present under the skin inside what is called follicle. Hence, even when it is removed from the skin, it starts to grow again as the living part of it is within the follicle under the skin. Cells inside the follicle divide and multiply. When the space inside becomes filled, the older cells exit the follicle forming the hair shaft. Thus, this shaft is actually dead tissue and a protein called keratin.
While the hair on the head keeps growing, that on the other body parts do not grow that much. This is because the growth of hair has two phases – anagen or active phase and telogen or resting phase. During the anagen phase, the hair grows. In the telogen phase, the growth slows down and falls off. There are varying durations of the active phase depending on the type of body hair. While the body hair’s anagen phase lasts only a few months, the scalp’s anagen phase lasts a few years.
New born babies develop hairs soon after birth and these fine ones are called vellus hairs. As they grow and attain puberty, the vellus turn into what are called terminal hairs. While vellus hair is fine and light colored, terminal one is thick, long and dark.
The hair on our body serves as a heat insulator and coolant. Hair on our head protects us from the sun's UV rays. To keep the body from overheating, we sweat. The fine hairs facilitate the sweat-cooling response.