A unique attribute of mammals, hair is particularly significant to humans, although its primary functions have become less important in modern times. Hair, so controversial that it spawned a musical, is of such concern that some people will spend thousands of dollars and a great deal of time to have it removed, while others go through a similar ordeal to have it replaced.

View a second image of a hair shaft section.

View a third image of a hair shaft section.

Each individual hair is divided into a hair shaft that protrudes from the skin and a hair root, which is the portion embedded in the skin. The root thickens at the end to become a bulb, which together with the underlying papillae, is responsible for the nourishment, development and growth of the hair. A dermal sheath of connective tissue surrounds the hair root, forming a hair follicle.

Hair is organized in three distinct tubular layers, the outermost of which is composed of dead, transparent cells known as cuticular scales. The innermost component is the medulla and consists of large, often distinctively colored cells that are interspersed with air pockets. Between the sections is the cortex, several layers of cells that may contain pigments or air bubbles. Specific characteristics, such as arrangement of scales, thickness of the cortex, and the color of medulla cells, vary greatly from species to species.