Hair, in mammals, is a characteristic threadlike outgrowth of the skin (epidermis) that forms an animal’s coat, or pelage. Mammals with fur, such as polar bears, dogs and cats, use their hair for thermal regulation or to serve as camouflage. In some animals, hair is used to provide sensory function or for communication purposes such as warnings and mating displays.
Human hair is a complex bio-synthesized material that contains keratin proteins and structural lipids. It consists of a number of layers that include the cuticle, the cortex and the medulla.
The medulla is a loosely packed and disordered region near the center of the hair that contains most of the fiber mass. The cortex is a dense, fibrous tissue that encases the hair shaft.
There are three growth phases in the life cycle of a hair: anagen, catagen, and telogen. Anagen is a phase of rapid growth; catagen is a phase of slow growth; and telogen is a phase of resting.
In anagen phase, the hair cells produce keratin to harden the structure of the shaft. Once the keratin is deposited, the cells push up into the hair follicle. The follicle nourishes the newly formed hair with blood from the papilla.
A hair follicle is a tiny cylinder that lives within the dermis of the body. It contains a hair root and a tiny muscle called the arrector pili. The arrector pili contracts in response to nerve signals from the sympathetic nervous system. This contraction makes the external hair shaft stand up, which provides insulation from cold.
The hair follicle can be felt by touching it with a finger. If the hair is very long, the feeling can be even more intense.
Hair can be seen in many different colors, shapes and styles. Some are wavy, straight, curly, dyed or cut in a variety of ways.
Some people prefer to have their hair done in a particular style or color. This can change their appearance and draw attention away from undesirable features or a poor social status.
In order to have a beautiful, shiny and healthy head of hair, people should follow proper hair care techniques. A good hair care routine includes washing the hair, shampooing and conditioning.
It should also be regularly brushed to prevent dandruff and other scalp problems. In addition, hair should be properly trimmed to avoid breakage and split ends.
The scalp, eyebrows and eyelashes are separate types of hair that develop fairly early in a person’s life. They protect the eyes by decreasing the amount of light and particles that get into them.
Hairs on the scalp grow at a rate of about 0.5 inch (13 mm) per month. The total number of hairs is between 100,000 and 150,000.
Some ethnic groups have a higher proportion of hair with dandruff or broken ends. These are typically the Indians, Chinese and Malay.