Final answer:
Lanthionization is the process by which hydroxide relaxers permanently straighten hair by breaking disulfide bonds, allowing hair to be reshaped and then reformed in a straight configuration.
Step-by-step explanation:
The process by which hydroxide relaxers permanently straighten hair by removing one of the bonded sulfur atoms in a disulfide bond is called lanthionization. This chemical reaction alters the disulfide bonds in the protein structure of hair, which are responsible for its natural curliness or waviness. By breaking these bonds, the hair can be reformed into a straighter shape. Once the bonds are broken, the hair is set in its new shape and the disulfide bonds are reformed in this new straight configuration using an oxidizing agent, such as hydrogen peroxide. Lanthionization is a permanent change until the hair grows out because new hair growth is not treated.