Hair

Hair is also a musical: see Hair (musical).

Hair is an outgrowth of the epidermis in mammals. Hair is a characteristic of all mammals, though in some species hair is absent at certain stages of life.

Hair serves a number of different functions. It provides insulation from cold weather and, in some species, from particularly hot weather. Because hair is often pigmented, it provides coloration. This might serve to camouflage an individual; in some mammals, the pigmentation changes with the seasons, becoming white during the snowy winter, for example. In humans hair is an adornment, while facial and pubic hair are both secondary sex characteristics. Patterns of hair also enable animals to identify others of their species; for example, the precise pattern of stripes on each zebra is unique.

The hair of many animal species is commonly referred to as fur.

Unlike other animals, human beings often cut their hair or shave it off.

The diameter of a human hair ranges from about 18μm to 180μm. Blond hair and red hair are at the thinner end of the scale, while black hair is the thickest.

The growth speed is roughly 10 cm/yr = 0.3 mm/day = 3 nm/s.