Final answer:
The permanent waving process of hair involves breaking and reforming disulfide bonds in hair proteins with chemicals, allowing hair to be reshaped into curls or waves that last until the hair grows out.
Step-by-step explanation:
Understanding Permanent Waves in Hair
The chemical process of permanent waving of hair primarily involves the breaking and reformation of disulfide bonds found in the hair's proteins. These bonds are present between the sulfur atoms in cysteine, which is an amino acid found in the keratin of hair. The process starts with the application of a reducing agent, usually ammonium thioglycolate, to break the disulfide bonds by adding a hydrogen atom to each sulfur atom. This step allows the hair to be shaped around rollers or curlers since the alpha-helices within the hair strands are no longer tightly cross-linked by the disulfide bonds.
Once the hair has been set on rollers to achieve the desired shape, an oxidizing agent like hydrogen peroxide is used to reform the disulfide bonds in their new positions, thus 'setting' the curly or wavy structure. Without this step, the hair would eventually revert to its original shape as the bonds naturally reform. As a comparison, heat from a hair straightener may break the hydrogen bonds in the hair, changing its shape temporarily until the hair is wet again, unlike the permanent changes made by altering disulfide bonds.
Answering a related question, disulfide bonds are harder to break than hydrogen bonds because covalent bonds, like disulfide bonds, are intrinsically stronger than hydrogen bonds, hence the necessity for chemicals to break them during the perm process. This difference in bond strength is also why hair straightening with heat, which breaks only hydrogen bonds, is temporary while perms, which break and re-form disulfide bonds, are permanent until the hair grows out.