Marylynn Kingsley, age 14, of Nampa, Ids., for her question:
WHAT GIVES COLOR TO A PERSON'S HAIR?
Hair is s substance that grows out of the skins of mammals. In the human, hair grows thickly on the top of the head. Men have hair on the lower parts of their faces and, in various degrees, on other parts of their bodies.
The color of your hair, its texture and the way it grows are determined by heredity.
The color of your hair comes from melanin, a pigment deposited in the hair cells as they form in the root. Melanin can produce hair colors ranging from blond to black.
As people grow older, pigment is no longer deposited in the newly forming hair cells. The hair gradually becomes gray or white.
Pigment is deposited in hair before it grows out of the skin. For this reason, there is no truth to the old story that says a person's hair can turn gray overnight.
Hair grows by forming new cells at the base of the root. As new cells from around the nourishing papilla, the old ones are pushed away and die. The new cells gradually force the rod of dead cells up out of the follicle. Thus, old cells from the root become part of the shaft.
Hair continues to grow as long as the papilla provides nourishment for new cells. The papilla may remain active for many years. A hair in the human scalp usually grows about one half inch each month for two to six years, although the period of hair growth is much longer for some persons.
The hair falls out when it stops growing and a new hair replaces it.
The shorter hairs of the body reach their greatest length and are replaced within a much shorter period. For example, an eyelash grows for only bout three to five months before a new eyelash replaces it.
Baldness results when the hair on a person's scalp is no longer replaced after it falls out.
Usually, after an old hair falls out the papilla again becomes active and a new hair appears. Many factors, including age, diet, general health and the condition of the skin, influence the activity of the papilla.
Baldness occurs more commonly in men than in women. The tendency to lose or retain hair, like the color of hair, is determined largely by inheritance. But other factors, including scalp diseases, exposure to radiation and glandular disorders can also cause baldness.
Doctors cannot cure hereditary baldness.
Excess hair on the face or body can be removed by electrolysis. In this process, an electric needle destroys the hair papilla. No new hair can then grow.
A depilatory is a chemical or combination of chemicals that can remove hair above the surface of the skin. The root of the hair remains alive and the hair will grow out again. Dipilatories may irritrate the akin and care should be taken when using them.