Perming works by inflicting damage to the structure of the hair by applying a solution that break the bonds that hold the keratin on the hair together. Another solution is applied to the hair for the keratin to fuse together according to the shape of the curlers, which gives the hair the perm. In time, perming can cause the hair to dry up and become brittle.
Perming was patented in the United Kingdom more than 100 years ago in 1909. Its patent holder, Charles Nessler, submitted for a patent for a "New and Improved Process of Waving Natural Hair on the Head." Perming has since become a standard service offered in most hair salons all around the world.
The hair is held together by a long, helical-shaped protein called keratin. The molecules of keratin group together to form protofibrils, which bind together to form microfibrils and macrofibrils. The keratin molecules are held together by a disulfide bond made from the residues of the amino acid cysteine.
The bonds that hold the keratin together are broken with a reducing agent called ammonium thioglycolate. This allows the keratin to be freely shaped into the direction of the curlers. The effect of the reducing agent is counteracted by applying a neutralizer, such as hydrogen peroxide. New disulfide bonds are formed to set the keratin back into place, only this time into the shape of the curlers, creating the perm.