Peter Weldon, age 1'1, of Fairfield, Conn., for his question:
WHAT IS HAIR MADE OF?
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. Determining just what your color will be is heredity with your parents and grandparents playing an important part in the decision. As some people get older, there is no pigmentation and the hair grows white or gray.
Hair is a substance that grows out of the skin in certain parts of a mammal's body. It may cover the entire body, as it does in the case of your family cat, or it may just grow in limited locations.
Some hair is called fur, fleece, bristles or quills.
Hair is made of the same kind of material that is used to make nails, claws and hoofs of mammals, the scales of reptiles and the feathers of birds.
Each hair is made up of a root and a shaft. The root of the hair is a soft, light colored bulb. The rest of the hair is the shaft. The root and a small section of the shaft lie below the surface of the skin in a sac called a follicle. At the bottom of the follicle a projection called the papilla contains an artery that nourishes the root of the hair.
The outside part of the hair shaft is called the cuticle. It is made up of a layer of flattened cells called cuticular scales. In most mammals, these cells overlap like shingles on a roof. Under the cuticle lies the cortex, a layer of tightly packed cigar shaped cells. The hair of most mammals has a central core, called the medulla, which is made up of loosely packed boxlike cells.
A cross section of hair, if you were to look at it under a microscope, would show that the hair varies in shape from round to flattened. Flattened hair shafts seem to grow at unequal rates in different places, making the hair curl or wave. The flatter the hair seems to be, the curlier it will be. Straight hair has a round shape.
Hair grows by forming new cells at the base of the roots. It continues to grow as long as the papilla provides nourishment for new cells. Hair of the human scalp usually grows about one half inch each month for two to six years. Then the hair falls out and a new strand of hair replaces it.
The shorter hairs of the human body reach their greatest length and are replaced within a much shorter period of time than are the long hairs on the head. For example, an eyelash will grow for only about three to five months, rather than two to six years, before a new eyelash replaces it.
Such factors as age, diet, general health and the condition of the skin can influence the growth of hair.