We only became fully aware of the hair strand structure through the use of a scanning electronic microscope which made it possible to view the inside of the hair and which produced a sharp three dimensional picture.

The hair strand has three layers:

• The cuticle or epidermis
• The cortex or middle layer
• The medulla or innermost layer

THE CUTICLE OR EPIDERMIS protects the inside of each hair. The cuticle is composed of 5-10 layers made from semi-circular curved scales, which cover and surround the hair strand. Under the scanning electronic microscope we noticed, between the scales, a plastic, amorphous, shapeless mass, which we named the KIT substance (bonding agent). This bonds the scales together and also the internal fibres. For healthy, normal hair these cuticle scales are positioned closely next to each other, so the hair is consequently smooth, shiny and easy to comb. Damaged hair does not contain sufficient amounts of the KIT substance and so looses its binding capacity. Because the scales are no longer linked together, they can flake off. Damaged hair is coarse, rough, without shine, difficult to comb and no longer has any resistance against harmful influences.

THE CORTEX OR MIDDLE LAYER is the largest part of the hair strand (70 to 90 %). In the cortex we noticed three division stages of the small fibres. PROTOFIBRILS are made up of MICROFIBRILS which themselves form into bundles called MACROFIBRILS.
The KIT substance bonds these small fibres together, which gives them elasticity. Natural pigments are found in the cortex (brown-black and red) and these give the hair its natural colour. A proportion of the distribution of pigments can be attributed to hereditary factors.

THE MEDULLA OR INNERMOST LAYER of the hair contains granules of fat and air bubbles. Thin hair does not have a medulla.

NATURAL HAIR COLOUR
Hair contains the natural pigment known as MELANIN. Small granules of melanin lie under the cuticle in the cortex between the fibrils. Natural pigment begins to form in the cells which are called MELANOCYTES and which lie between the papilla and the hair root. Melanin starts with the oxidation of a basic colourless pigment substance which makes it way into the hair papilla from blood carrying veins. This basic colourless pigment substance is, according to its chemical structure, a protein which accumulates in the protoplasma cells in the form of brown granules. Under the influence of fermentation of the cell layer on the surface of the skin it oxidises into a brown pigment and then to a black colour, and we call this EUMELANIN.
Besides the natural pigment melanin, hair also contains a red pigment called PHEOMELANIN. These two pigments can be differentiated between according to their shape and chemical reactivity. During bleaching and colouring the red pigment oxidises with greater difficulty into very light colour shades, therefore the hair remains a yellowy-orange colour.
In old age the natural pigments stop being produced. Hair is completely white if it grows without pigment formation, but if the formation of natural pigments gradually diminishes and is partially interrupted, then the hair becomes grey (although there is still a residue of brown-black pigments).