What is the main chemical action of relaxers on hair?

The main chemical action of relaxers on hair involves breaking disulfide bonds. Disulfide bonds are the chemical links that provide structure and strength to the hair's keratin fibers. When relaxers are applied, they penetrate the hair shaft and chemically alter these bonds, causing the hair to become more pliable and straight. This is essential for achieving the desired straightened or relaxed effect, allowing the hair to be reshaped and styled more easily.

The other options, such as strengthening the hair shaft or hydrating it, do not accurately describe the action of relaxers. While there are hair products designed to strengthen or hydrate hair, their mechanisms differ from that of relaxers, which specifically target and modify the disulfide bonds to achieve straightening. Adding volume is also not a function of relaxers; in fact, the straightening process often results in a sleeker, flatter look compared to the natural volume of curly or wavy hair. Therefore, breaking disulfide bonds is the key chemical action of relaxers, making it the correct choice.