DRY, damaged, oily, blond? When it comes to hair type only thickness and dye really matter.
That's according to researchers at Procter & Gamble, who have used atomic force microscopy - which generates nanoscale images - and micro-CT scanning to analyse the interactions between chemicals and hair fibres. They found the most significant differences are between thick, fine and coloured hair.
Hair is usually coated with a protective layer of oil that is uncharged and repels water. Bleach and dye strip away this layer, causing hair to become negatively charged and attract water. This means that uncharged chemicals such as silicone - added to shampoo to make hair soft and shiny - will no longer stick. This has led to the development of amino silicones, whose charge means they do stick to coloured hair (International Journal of Cosmetic Science, DOI: 10.1111/j.1468-2494.2010.00540.x).
The scans also showed that fine hair funnels water, so ingredients in shampoo need to be extra sticky to have any effect. Thick hair creates a kind of sieve so ingredients need to be bigger to work their magic.
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