Despite the important role of hair in protecting you from your environment (cold, heat, the sun's rays), you are probably most aware of its impact on your appearance. Social norms dictate how much hair is acceptable and where it is acceptable on the body For instance, short hair may be one year and out the next. The hair care industry is thriving and it brings with it annual trends in hair styles and hair care products. In North America today, it is not acceptable for women to have hair in the armpits or on the legs, whereas in the 1960's this trend was partially reversed, as the style of the day focussed on the natural look. Men with hairy chests are considered masculine but even this is subject to socially acceptable limits.

Hair is an integral part of the structure of your skin and, like your skin, it changes with the passage of time. A single strand of hair is made of several components: the hair shaft (the visible part of the hair) is dead; the hair follicle (sac) and the portion of the hair below the skin's surface is a single structure which lives and grows at an average rate of I to 3 centimeters (1/2 to 1 inch) per month. The hair follicle is an appendage of the epidermis of the skin. It extends into the dermis, from which it receives its blood supply and sensitivity through the surrounding network of nerves.

Hair develops in three phases: a growing phase, a transition phase, and a resting phase during which the hair is shed. On average it takes a single scalp hair one to two years to pass through all three developmental phases. Although you shed hair every day, it grows back at about the same rate as you lose it. An adult has an average of about 100,000 head hairs and they are lost and replaced at a rate of approximately 100 hairs a day, under normal conditions. Hence the hairs which are found on the shower floor and tangled in hair brushes each day Hair also tends to grow faster in the summer than in the winter.

Hair varies from individual to individual in color, texture, and amount. Redheads tend to have fewer hairs than do brunettes or blondes, but their hair is much coarser in texture. Blondes, on the other hand, have finer hair but lots of it. Brunettes fall somewhere between blondes and redheads.

Hair changes in color and amount with age. These changes can be distressing because they are highly visible signs of aging. They occur both in men and women but the norms of acceptability differ for each sex. For example, greying hair tends to be more acceptable in men than in women. Superfluous or unwanted hair is of particular concern to women, since hair on the face, around the nipples, and above the pubis is generally considered to be unacceptable. Hair loss is more apparent in men because it is regional, whereas in women it is more diffuse.