Hair Dyes
John Emsley looks at the chemistry behind familiar, everyday products
The global market for hair dyes exceeds £4 billion annually with the biggest manufacturer, L'Oréal taking just over a third of world sales. Hair dyes are of three kinds: temporary, semi-permanent, and permanent. The first of these are easily washed out of the hair, the second will survive several washings but eventually fade, and the third are locked fast within the hair shaft and disappear only as the hair grows out.
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