Why does hair go curly when wet? © Getty Images

What makes hair go curly when it’s wet?

The molecules in your hair are held together by strong chemical bonds, some of which are sensitive to water and can temporarily change their shape.

Asked by: Aaron Billson, Cannock

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The shape of your hair reflects the shape of the molecules of which it is made. These are long keratin molecules (a type of protein) that resemble a long spring, with several ‘springs’ wrapped around each other like a twisted rope. The strands are held together by strong chemical bonds called disulphide bonds, while the coiling of the individual molecules is maintained by much weaker hydrogen bonds. The disulphide bonds can only be broken with heat (as happens in ‘permanent waving’ hair treatment), but hydrogen bonds are affected by water, so the individual molecules can change their shape temporarily when wet.


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