Hair is present in differing degrees on all mammals, and its most important function in those other than human is to conserve body heat by insulating against cold. Humans are the most hairless of all mammals, and yet hair occupies a central place in human development and sense of self.

Hair types and styles have, at various times, in various countries and on various continents, come to be associated with definitions of race, the possibility of being or becoming the right kind of woman, with radicalism or revolution, and with the right to occupy a particular social space in a class hierarchy. While often discussed as a personal statement of style or fashion, humanity's relationship to hair is far more complicated.

During the monarchy in France, the prince's hair, for example, was never cut — it was curled and pampered. Rastafarian followers of the early twentieth-century Ethiopian religious leader Haile Selassie not only refused to cut theirs, but were forbidden to comb it either. Early records indicate that the ancient Egyptians, men and women alike, shaved their hair off and wore wigs. As a sign of respect for the law and British custom, judges and lawyers during America's colonial period wore powdered wigs over their natural hair. Rapunzel let her hair cascade out of a window and down a tower so that Prince Charming might climb up and rescue her from imprisonment. Among the Yoruba people, hair signifies aesthetic value; and for East African pastoral peoples, such as the Pokot and Samburu, its styling indicates age status. A 1970s American Broadway musical, Hair, received numerous awards and set records for attendance.

Individual human hairs vary in colour, diameter, and contour. The different colours result from variations in the amount, distribution, and type of melanin pigment in them, as well as from variations in surface structure that cause light to be reflected in different ways. Hairs may be coarse, or so thin and colourless as to be nearly invisible. Straight hairs are round in cross section, while wavy hairs are alternately oval and round; very curly and kinky hairs are shaped like twisted ribbons. During the nineteenth century, renowned social scientists posited relationships between some of these variations in hair type and intelligence, or the potential for civilized behaviour, and indeed, in some instances, saw them as a marker of humanness.

Each hair grows from a hair follicle in the deep layer of the skin. There are different types of hair at different stages in life, and in different parts of the body. The first to develop is the lanugo, a layer of downy, slender hairs that begin growing in the third or fourth month of fetal life and are entirely shed either before or shortly after birth. During the first few months of infancy appears fine, short, unpigmented hairs called down hair, or vellus. Vellus covers every part of the body except the palms of the hands, the soles of the feet, undersurfaces of the fingers and toes, and a few other places. At and following puberty, this hair is supplemented by longer, coarser, more heavily pigmented hair, called terminal hair, that develops in the armpits, genital regions, and, in males, on the face and sometimes on parts of the trunk and limbs. 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. On the scalp, where hair is usually densest and longest, the average total number of hairs is between 100 000 and 150 000. Human hair grows at a rate of 10-13 mm/month.

In addition to the presence or absence of hair, hair texture and styling have played a long and important role in human history. It is not clear just why hair has come to mean so very much to so many people, but there is no mistaking the important role that hair has played in the process of identifying a relationship to a particular culture or subculture. Hair can lead to acceptance or rejection by certain groups and social classes, and its styling can enhance or detract from career advancement. Products such as hair extensions have gained massive popularity in recent years due to the importance placed on hair.

Hair Condition