Once in the cortex, the waving solution breaks the disulfide bonds through a chemical reaction called?

• A. Reduction
• B. Oxidation
• C. Hydrolysis
• D. Polymerization

Answer: (A)

Disulfide bonds in hair keratin are broken by a reduction reaction. The waving solution uses reducing agents to donate electrons to the sulfur-sulfur (S-S) bonds, turning them into two thiol groups (R-SH) and thus cleaving the cross-links. This break allows the hair to be reshaped. Oxidation would instead form or restore these bonds, hydrolysis would target bonds with water but not specifically disulfide cross-links in this context, and polymerization would join chains rather than break the S-S bonds. So the waving solution works through reduction.