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| Hair Styling Products
The outer part of the hair shaft is called the cuticle and consists of flattened scales of keratin. In normal hair the scales are open when wet and closed when dry. If the hair is damaged, the scales may be permanently open, making the hair porous (able to absorb water). The scales are translucent (allow light to pass through) but if the hair is damaged the scales point in different directions and so light is refracted at different angles through the cuticle – making the hair appear dull, rather than shiny. Inside the cuticle is the cortex, which contains the coloured fibres that give the hair its colour. These fibres are joined together with weak bonds that give the hair its shape and elasticity. If the hair is porous, these bonds become damaged by moisture and hair will over-stretch and not bounce back. Different types of melanin give the hair its colour. In the centre of the hair shaft there is also often a fibrous honeycomb structure called the medulla. On average, human hair grows at about 12mm per month, and faster between the ages of 50 and 69, after which it can slow down. The average human head has between 90,000 and 180,000 hairs but we lose approximately 100 of these each day; but they do re-grow … unless you’re balding! Nowadays, we wash our hair on a regular basis to remove dirt and grease, but this was not always the case. Shampoo only became popular in the 1930s and before this hair may only occasionally have been washed with alkaline soap to remove dirt. Many people now follow shampoo with conditioner, which contains oil that lies along the scales of the cuticle and helps it to lie flat; therefore making hair shiny and easy to detangle. This protects the hair and seals in moisture by creating a barrier around the cuticle. Hair gels and waxes also smooth the hair cuticle by coating the scales, enabling them to be manipulated so that they all lie in the same direction. They also fill in some of the damaged gaps in the cuticle layer, thereby giving sleek, shiny and manageable hair. Since the ancient Romans and Greeks, people have styled their hair using different greases and oils which they used to protect their hair, make it shiny and easier to comb. More recently, a mixture of sugar and water has been used, as well as tragacanth gum (a type of gum extract). In the 1950s a new type of styling product was produced, containing tiny resin-like particles of plastic suspended in alcohol. This formed a coating around each hair strand, protecting it and improving both texture and body. Styling products temporarily change the shape of hair. The polypeptide chains in the cortex of the hair shaft, which are held together by hydrogen bonds, separate when wet and then join up with their nearest neighbours to make new bonds when dry. These bonds remain in their new position so long as the hair remains dry. Therefore hair that is styled from wet tends to hold its shape until dry. By adding a protective layer of styling product over the outside of the hair shaft, this new shape can be held for longer as the product prevents moisture entering the hair and changing the hydrogen bonds.
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