The Scientific Processes During Perming & Relaxing

The hair perming process
Perming process - Photo: Shutterstock
As we know, the hair is made up of protein chains held together by series of physical and chemical bonds which give the hair its shape and strength. The bonds we are most concerned with in styling the hair are the side bonds.
Side bonds are found in two forms – physical side bonds and chemical side bonds. Breaking and reforming these side bonds allow us to rearrange the wave pattern of the hair. Physical side bonds can be broken using heat and water and reform when the hair dries and/or cools.
However, this article is about perming and relaxing and the scientific processes that occur. When the hair is permed (and sometimes when straightened) the disulfide bonds (the chemical side bonds) of the hair are broken through a chemical reaction called ‘reduction’. A reduction reaction involves either the removal of oxygen or the addition of hydrogen. In the case of permanent waving, the reduction is due to the addition of hydrogen.
The disulfide bonds join one sulfur atom on one polypeptide chain to another sulfur atom on different polypeptide chain. Perms use reducing agents called thiol compounds, which break the disulfide bonds by adding a hydrogen atom to each of the sulfur atoms in the disulfide bonds. With the disulfide bonds broken, the polypeptide chains are able to slip into their new shape.
The broken disulfide bonds are reformed through the neutralization of the thio compound used to break them. The most common neutralizer is hydrogen peroxide and the chemical process that removes the hydrogen atoms and reforms the disulfide bonds is called “oxidation”.
Oxidation can result in the lightening of the hair color – especially if a strong thio compound was used – and this is why the hair should be rinsed carefully and blotted thoroughly before applying the neutralizer. The oxidation reaction combines the hydrogen and oxygen atoms in the peroxide molecules with the hydrogen atoms used to break the disulfide bonds to form two separate molecules of water. (Peroxide {H2O2} + Hydrogen + Hydrogen {+ H + H} = Water {H2O + H2O})
The removal of the hydrogen atoms from the sulfur atoms forces them to reform their disulfide bonds in the new shape (around the perm rods). The process is the same for relaxers and straighteners that use thio compounds, except that these are removing curl rather than creating it.
Hydroxide relaxers break the disulfide bonds in the hair by removing one atom of sulfur from the disulfide bond and thereby converting it into a lanthionine bond. This process is called lanthionization. When a hydroxide relaxer breaks a disulfide bond the bond is permanently broken and can never be reformed.
Hydroxide relaxers leave the hair extremely alkaline even after rinsing. To restore the pH balance of the hair, an acid-balanced shampoo or normalizing lotion neutralizes any remaining hydroxide ions to lower the pH of the hair and scalp. Some neutralizing shampoos intended for use after hydroxide relaxers have a built-in color-change indicator to show when the hair’s pH has returned to normal.
The neutralization/normalizing process with hydroxide relaxers never uses any oxidation, in fact, oxidizing agents can seriously damage hydroxide relaxed hair.
Stacy - Hair Stylist     ©
See also:
How perms work
The natural pH level for hair
A guide to permanent waves