For more lasting changes to your hair style—and your hair chemistry—you must turn to permanent waving (perming) or straightening. These processes not only alter hair's hydrogen bonds but also split apart stronger chemical bonds that are unaffected by water. Although waving and straightening (also called relaxing) produce opposite results, the two procedures employ the same chemical tricks.
Whether hair is permed or relaxed, the first step, called softening, involves reduction. Reduction is a chemical reaction that adds hydrogen to a chemical compound. In the perming or straightening process, reducing agents, sometimes together with heat, break the hair's water-stable bonds—primarily the sulfur-to-sulfur links in cystine.
In the next step of the process, called rearrangement, the keratin chains are molded into the desired configuration. This is accomplished by winding the softened hair on rods to produce curls or holding it flat to straighten it.
The final step, hardening, makes the rearrangement permanent by rebuilding the sulfur-to-sulfur bonds and other water-stable molecular links that hold hair strands together. This is accomplished through oxidation—a chemical reaction that reverses reduction by adding oxygen to a compound. For perms and relaxers, the chemicals that initiate oxidation are either sodium bromate or hydrogen peroxide solutions.
Although perming and straightening are called “permanent,” perms and relaxants do not change the hair matrix. Thus, their effects eventually disappear as hair grows out.
When properly formulated and used according to directions, products that perm or relax hair should not change its color or significantly weaken it. But both hair and scalp can be damaged if such products are carelessly manufactured or applied. In 1995, for example, the U.S. Food and Drug Administration (FDA) warned against the use of two hair relaxers sold under the name of Rio Hair Naturalizer System. The FDA took that action after more than 1,800 consumers complained that the products had irritated their scalp, caused their hair to break off, or turned it green. FDA investigators found that the products contained too much acid and were improperly labeled.