If you're one of my loyal readers who's gone to the trouble of Google-stalking me, you'll probably realise I'm kind of known for my brightly coloured hair. Blues, pinks, purples - the brighter the better.
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While you may think of hair colouring as just one of the trappings of vanity, there is actually some quite interesting chemistry behind my colours.
To understand how hair dye works, you first need to know a little about what hair is made of. Hairs are long fibres made mostly of a protein called keratin. Each fibre is made of a few different layers.
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Right at the centre is the medulla, which is surrounded by the cortex, which is the main structural part of hair. The cortex of the hair also contains melanin, which gives hair its colour. This in turn is surrounded by an overlapping layer of cells known as the cuticle.
Different types of hair dyes work differently and effect different parts of the hair strand.
Temporary or semi-permanent dyes deposit colour into the cuticle of the hair. Because the pigment molecules are on the hair surface, these products can be shampooed out (eventually). And because they don't interfere with the pigment molecules in the cortex of the hair, the hairs natural colour remains once the dyes are washed out.
Permanent dyes are a different story. These products open up the cuticle of the hair to allow colour to be deposited into the cortex of the hair.
This takes place through a number of steps. Ammonia is generally used to loosen the cells of the cuticle and make the hair porous. Peroxide then strips the natural colour from the hair by turning the normal pigment molecules colourless.
Dye molecules can then be deposited into the hair cortex, and the hair can be conditioned to tighten the cells of the cuticle again, trapping the colour within.
I'm often asked if I'm worried about the long-term effects of exposure to the chemicals in hair dyes.
The short answer is no. As long as they're used properly the health risks are very small. No scientific studies have yet found a conclusive link between use of hair dyes and an increased risk of disease - even in hair dressers, who are exposed to these products day in and day out. When the science tells me to stop, I will.
But for now, life's too short for boring hair.
Dr Mary McMillan is a lecturer at the School of Science and Technology, University of New England
