Hair Bleach: How does hair lightening work?

Hydrogen peroxide, a type of bleach, has a variety of applications in industry - one of which is to remove colour from hair

Hair is made from a tough protein called keratin, the same material that makes up your nails and the outer layer of the skin. Hair colour is determined by the ratio of the pigments eumelanin (responsible for black and brown pigments) and phaeomelanin (which produces yellow and red pigments). Without either type of melanin, hair becomes grey or white.

Bleach lightens hair by oxidising the melanin molecules. The melanin pigment is still present within the hair, but once oxidised it is colourless, leaving just the pale yellow tint of the keratin protein. Bleach is particularly useful in changing darker hair to lighter hair, but if not used properly it can lead to damage. If left on for too long, bleach will react with the moisture within the shaft of the hair, leaving it dry, brittle and frizzy.

This article was originally published in How It Works issue 106, written by Charlie Evans

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