Hair is a
filamentous biomaterial that grows from
follicles found in the
dermis. Hair is one of the defining characteristics of
mammals. The human body, apart from areas of
glabrous skin, is covered in follicles which produce thick
terminal and fine
vellus hair. Most common interest in hair is focused on
hair growth, hair types and
hair care, but hair is also an important
biomaterial primarily composed of protein, notably
keratin. Attitudes towards hair, such as
hairstyles and
hair removal, vary widely across different cultures and historical periods, but it is often used to indicate a person's personal beliefs or social position, such as their age, gender, or religion
The word "hair" often refers to two distinct structures:
- the part beneath the skin, called the hair follicle or when pulled from the skin, called the bulb. This organ is located in the dermis and maintains stem cells which not only re-grow the hair after it falls out, but also are recruited to regrow skin after a wound;[2]
- the shaft, which is the hard filamentous part that extends above the skin surface. A cross section of the hair shaft may be divided roughly into three zones.
Hair fibers have a structure consisting of several layers. Starting from the outside:
- the cuticle which consists of several layers of flat, thin cells laid out overlapping one another as roof shingles,
- the cortex, which contains the keratin bundles in cell structures that remain roughly rod-like; and in some cases,
- the medulla, a disorganized and open area at the fiber's center.[