The basic structure of hair

Human hair has three distinct parts:

The cuticle

This is the protective outer coating of the hair. It is the part that you can feel and if it becomes damaged it feels rough so the hair feels dry.

The cuticle is made up of layers of cells that overlap like tiles on a roof. Some hair can have as many as eleven layers of cuticle cells while other hair has less.

If the cuticle has many layers or if it is tightly packed then the hair may be resistant because it may be difficult for chemicals such as colours or relaxers to get underneath the cuticle and into the cortex to do their work. Hair that has damage to the cuticle, or has cuticle that is missing will be porous.

The cuticle is colourless but it is translucent; this means that it lets some light through so you can see the cortex.

The cortex

This is the largest and main part of the hair, the place where all the chemical changes occur.

It is underneath the cuticle and the natural colour pigments (which can be seen through the translucent cuticle) are found in the cortex. The granules of colour pigment are known as melanin.

The cortex consists of long chains of cells that form in a spiral into fibres. These fibres spiral together into fibre bundles and groups of these bundles form the hair.

The fibre bundles are held together inside the cortex by different types of bonds –the weak salt and hydrogen bonds, (these are broken by water or heat) and the very strong disulphide bonds that can only be broken by chemicals such as perm lotion or relaxer.

The medulla

This part of the hair is not important so far as hairdressing is concerned. It has no effect on any hairdressing processes and is not always present in the hair. Some hair, when examined under a microscope, shows the medulla in patches – present at some points, absent at others.