Hair grows on the head or in the beard at about 4 mm a week. Hair usually contains pigmentation making the hair appear black, or brown or red, or blonde. In aging follicles there is little or no pigmentation of the hair and the hair is then white. Oil glands in the skin can secrete a covering to the hair making it appear glossy. People differ in the extent of their hair covering.
Hair can slow the cooling of the skin and also give protection against sun burn.
It can also prevent abrading of the skin when parts of the body rub against each other as in walking or arm movements against the chest. At puberty there is increased hair growth in the arm pits, around the genital areas, and on the faces of men. This is to advertise our sexual maturity. Hair was probably functionally more important before we developed clothes or when we lived in a warmer climates. The different coloured hair also helps in the identification of people.