The structure of the hair
The hair is made from polypeptide chains – a keratinised protein. There are millions of these in every strand of hair. They are held together by different types of bonds.
The two types of bonds that are the most important are:
- Hydrogen- weak bonds that give the hair its temporary shape
- Disulphide- strong bonds that give the hair its permanent shape.
When styling the hair we deal with hydrogen bonds. These are broken down by water only.
When the hair has been shampooed, water penetrates through the cuticle into the cortex. This then breaks down the weaker hydrogen bonds that are found in the cortex.
- Hair in its natural or relaxed shape is called Alpha keratin
- Hair in a stretched state after blow drying or setting is called Beta keratin
- Hair will go back to Alpha keratin as it absorbs moisture
Below the surface of the skin is the hair root, which is enclosed within a hair follicle.
At the base of the hair follicle is the dermal papilla. The dermal papilla is supplied with nourishment from the bloodstream to produce new hair. The dermal papilla structure is vital to hair growth because it contains receptors for male hormones and androgens.
Androgens regulate hair growth. In scalp hair, the androgens may cause the hair follicle to become progressively smaller, causing the hair to become finer in individuals who are genetically predisposed to this type of hair loss.
The hair shaft is made up three main layers, two of which are vital: the Cuticle and the Cortex layers.
The cuticle
Is made of transparent overlapping scales which protect the hair. Chemicals lift and close the cuticle to allow chemicals to penetrate the cortex. Heat also opens the cuticle.
The cuticle scales ideally should be closed from root to tip to give hair shine and lustre. Healthy hair reflects light and damaged cuticle scales will make the hair feel porous and appear dull.
Key characteristics of the cuticle-
- In good condition they are water repellent
- When damaged will allow more water to be absorbed into the hair
- A single layer of ‘scale’ like cells that overlap from root to point
- They make the hair shine when flat and closed
- Can be raised to allow liquids to enter the hair shaft
The cortex
This is the section under the cuticle and is where most of the action happens. Your naturel colour is determined in the cortex and this is where artificial colouring mostly takes place. It is this layer that has the bonds which hold your hair in place to determine if your hair is straight , curly or wavy. It is the main part of the hair that gives it its strength and elasticity.
The medulla
This is the least interesting layer. It is the central part of the hair but is not always present. In a single strand it may fade in and out or be present the whole way through. In thicker hair it appears more often than not.