Hair

           Bouncy, shiny hair is usually a sign of a well-nourished person in good overall health. Dry, dull, and lusterless hair often belongs to malnourished people in poor health.
Hair is a slender threadlike outgrowth of protein from the skin in mammals.
Hairs are not permanent structures but are continually replaced throughout the life of a mammal.
If hair grown is dense profusion in some animals, is called as fur or wool.
There are varieties of cats, dogs, and mice bred to have little or no visible fur. In some species, hair is absent at certain stages of life.


Types of Hair
Hair grows from hair follicles deep in the dermis. There are different types of hair at different stages in life, and in different parts of the body.
Lanugo: a layer of downy, slender hairs. Lanugo hair grows in the third or fourth month of fetal life and is entirely shed either before or shortly after birth.

Down Hair or vellus:
fine, short, unpigmented hairs
appears during the first few months of infancy.
Vellus grows in most places on the human body in both sexes except the palms of the hands, the soles of the feet, undersurfaces of the fingers and toes, and a few other places.

Terminal Hair:
Terminal hair, fully developed hair. At puberty Vellus hair is supplemented by longer, coarser, more heavily pigmented hair.
Terminal hair develops in the armpits, genital regions, and, in males, on the face and sometimes on parts of the trunk and limbs.


The most important function of hair in human is to conserve body heat by insulating against cold. Human hair carries a central place in human development and sense of self. Whether it is the gradual decrease of hair leading to male baldness, the loss of pigment leading to white or grey hairs and signalling the onset of middle age, or the adolescent desire for the pubic hair that signals approaching adulthood.

Hair Growth:

The growth and the distribution of hair are under the influence of the sex hormones. The hair of the scalp, eyebrows, and eyelashes are of separate type and develop fairly early in life. There are different types of hair grown at different parts of the human body.
Vellus hair appears during the first few months of infancy.
Vellus grows in most places on the human body in both sexes except the palms of the hands, the soles of the feet, undersurfaces of the fingers and toes, and a few other places.
The density of the hairs (in hair follicles per square centimeter) varies from individual to individual.

In male, hair follicles respond to androgens, primarily testosterone and its derivatives; the hair in these locations can be thus termed androgenic hair. Increasing androgens hormones, transforms vellus hair into terminal hair on several parts of the body.

Different areas on body respond with different sensitivities. Increasing testosterone hormones levels, the sequence of appearance of androgenic hair reflects the gradations of androgen sensitivity. In human pubic area is most sensitive, so heavier hair grows there first in response to androgens.

Rising androgens in both sexes, men and women, develops terminal hair in the pubic area and under the arms. In contrast, normally only men grow androgenic hair in other areas.