The Hair Shaft

The hair shaft consists of the medulla, cortex. Immediately above the matrix cells, hair shaft cells begin to express specific hair shaft keratins in the prekeratogenous zone [23]. The medulla is a central part of larger hairs, such as beard hairs, and a specific keratin expressed in this layer of cells can be controlled by androgens [24]. The cortex is composed of longitudinally arranged fibres. The hair shaft cuticle covers the hair, and its integrity and properties have a great impact on the appearance of the hair. It is formed by a layer of scales that interlock with opposing scales of the inner root sheath, which allows the hair shaft and the inner root sheath to move upwards together.