The hair shaft is the cylindrical, keratinized, often pigmented filament that can be seen above the skin. Under the microscope the crossection of hair shows that the hair shaft has a form of elongated cylinder or tube consisted of keratin cells. As we know the hair shaft is very strong - it stands tension, perming, exposure to chemicals and ultraviolet radiation. The hair shaft may have a different angle of growth in relation to the skin of the head surface - an angle from 10 to 90 degrees. If there is a very small increase in the angle of 10-20 degrees, it is quite difficult to create the desired hair style, also to simply comb hair or evn shave them. This angle of growing hair during the whole life span doesn't chane or change very little. Hair shafts also show extreme variations in color, diameter, and transverse contour. Some hairs may be almost perfectly round while others are so markedly flattened or oval that they resemble ribbons. Twisting of such ribbon like hairs along the longitudinal axis may give the impression that the hair varies widely in diameter, although this is usually not the case, except in certain pathological conditions. Hair shaft consists mainly of dead cells that have turned into keratins and binding material, together with small amounts of water. It is composed of three main layers. From outermost to innermost part of a hair fiber - the cuticle, the cortex, and the medulla (only present in large terminal hairs, i.e. hairs greater than 60 microns in diameter). Medium cortical layer of the hair is the thickest of these three layers. It is composed of many fibers and cell nucleis, also it contains the hair pigment - melanin, which determines hair color. Together all these layers perform specific functions in the hair structure - cuticle protects against external factors, so acts as a "skin"; cortical layer is the main layer of hair, so acts as a "body" of hair; as well as the hair cortex pigment in its function is similar to skin pigment; and the inner layer medulla is a completely different structure - like a "brain" substance for hair. More information about the internal structure of the hair shaft you will find in hair sfaft structure section.

 

The structure of the hair shaft: 1 - cuticle - the outer layer; 2 - cortical layer fibers; 3 - cortical layer cell nucleus; 4 - medulla - the inner layer; 5 - cortex - the middle layer; 6 - hair pigment - melanin.