The shape of a hair depends on several factors, including the shape of the hair follicle and its opening; these vary from one person to another and also between races. As keratin is hardening it is compressed into the shape of the hair follicle. The hair is then held in shape by the pattern of the chemical bonds within it. Of these, the disulphide bonds are the strongest. They can only be changed by chemical methods such as perming or relaxing.
But within each hair the keratin chains are also linked by bonds of a different kind, called hydrogen bonds. There are far more hydrogen bonds than disulphide linkages. The hydrogen bonds are much weaker than the disulphide linkages and more easily broken, and they give hair its flexibility. Hydrogen bonds are broken apart whenever the hair is wetted, and form again as it dries. When they break the shape of the hair changes. If the wet hair is then wound on to rollers it will form a new shape, and if it is dried on the rollers it will keep this shape.
This is the basis of the setting process. The change in shape is only temporary. It is lost when the hair is dampened, because the new hydrogen bonds are broken again.
But within each hair the keratin chains are also linked by bonds of a different kind, called hydrogen bonds. There are far more hydrogen bonds than disulphide linkages. The hydrogen bonds are much weaker than the disulphide linkages and more easily broken, and they give hair its flexibility. Hydrogen bonds are broken apart whenever the hair is wetted, and form again as it dries. When they break the shape of the hair changes. If the wet hair is then wound on to rollers it will form a new shape, and if it is dried on the rollers it will keep this shape.
This is the basis of the setting process. The change in shape is only temporary. It is lost when the hair is dampened, because the new hydrogen bonds are broken again.