Hair

Hair is a protein filament 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.

Structure

The structure of hair can be broken down into three parts: the cuticle, the cortex, and the medulla.

Cuticle

The cuticle is the outermost part of the hair shaft. It is formed from dead cells, overlapping in layers, which form scales that give the hair shaft strength and protect the inner structure of the hair.

Cortex

The cortex contains the keratin bundles in cell structures that remain roughly rod-like. This part of the hair contains the most melanin, giving the hair its color.

Medulla

The medulla is the innermost part of the hair shaft. This nearly invisible part of the hair exists in different forms in different hair types and could be absent entirely in some hair.

Growth

Hair growth begins inside the hair follicle. The only "living" portion of the hair is found in the follicle. The hair that is visible is the hair shaft, which exhibits no biochemical activity and is considered "dead".

Function

Hair has a number of functions: it can serve to protect the skull, it can help control the body temperature, and it can help to evaporate perspiration.

Hair disorders

There are many types of hair disorders, including alopecia, hirsutism, and telogen effluvium.

See also

• Hair follicle
• Hair diseases
• Hair transplantation

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