Within the body of the hair, the cortex, the keratin is organised into protofibrils, composed of 4 chains of keratin. This assembly is held together by bonds or bridges between the atoms of the different chains. These bonds may be of variable strength: weak bonds such as hydrogen bonds can be distinguished from the stronger ionic bonds and sulphur bridges. It is by acting on these bonds that the shaped of the hair can be modified, by adding moisture for a short term difference, or by using heat for a longer lasting result.
