The process of using chemicals to break down hair structure for a permanent wave is perming.
A perm changes the shape of hair by temporarily breaking disulfide bonds in keratin, the protein that gives hair much of its strength and elasticity. Hair is wrapped around rods, treated with a reducing lotion, and then exposed to a neutralizer—often hydrogen peroxide—that reforms bonds in the new shape.
The modern cold wave was developed by Arnold F. Willatt in 1938 and used ammonium thioglycolate rather than a large heating machine. Today, sodium thioglycolate is also common. Rod size and wrapping method determine whether the result is a tight curl, loose wave, or spiral pattern.
“Perming” is often confused with relaxing, but the two processes aim for opposite shapes: perming creates waves or curls, while a chemical relaxer straightens hair. Both alter the same keratin structure and can weaken hair when overused.