CUTICLE
The cuticle layer is the outermost layer of the hair and envelops the inner layers. Its tough, dense structure protects the hair. 6 to 10 layers of flat cells surround the cortex. They are arranged in a similar fashion to roof tiles. The outermost, exposed edges are open to the tip of the hair. The cuticle layer is colourless and therefore permits the light to shine through. It makes up a good 10 percent of the hair’s diameter.
The cuticle layer is important for the shine and elasticity of the hair. In young hair near the scalp, the edges of the cells lie flat on one another. The hair is only slightly porous and feels soft and supple. The surface reflects the light giving the hair its shine. The older a piece of hair is, the more physical and chemical stress it has been through. The edges of the cells open along the length and at the tips of the hair, or they are worn away. The hair becomes porous and feels straw-like and rough. It loses its gloss because the uneven surface no longer reflects the light evenly.
CORTEX
The cortex is the thickest of the three layers and makes up about 80 to 90 percent of the hair’s diameter. Hardened fibrous cells are bundled together. Every fibrous cell is made up of thousands of protein molecules. These long fibres are twisted together in bundles. The fibrous bundles are surrounded and held together by a mass of softer keratins. The cortex also contains the colour pigment melanin, which gives the hair its natural colour. White hair has no pigment and contains no melanin.
MEDULLA
The medulla is in the center of the hair. Its diameter varies according to the thickness of the hair. In thick hair it is like a canal and gives the hair its stiffness. In fine hair it is only partly there or completely missing.