The exterior part of normally developed hair is the hair trunk, which represents the ‘’dead’’ part of hair. If we look at the horizontal cross-section of hair, it can be seen clearly that the hair trunk is made of three layers. The exterior layer is the cuticula: it consists of only one layer of transparent epitel cells. The middle layer is the cortex: the main structure consists of dead cells (80% of the composition is keratin, which consists of amino acids cistine, serine, glutamine …). The interior layer is the medulla.

Horizontal hair cross section

Hair Function

Besides decorative, the main function of hair is to prevent excessive loss of temperature. Hair makes an insulation layer and keeps in that way air to the skin surface.