Permanent waving and chemical hair relaxing change the shape of the hair by chemically changing the

• A. Hydrogen bonds
• B. Salt bonds
• C. Disulfide bonds
• D. Peptide bonds

Answer: (C)

Hair shape is held by several types of bonds in keratin, but the bonds that determine permanent form are the disulfide bonds. In perming or relaxing, a reducing agent breaks these strong cross-links between sulfur atoms in cysteine units, allowing the hair to be reshaped around rods or into a new straight configuration. After the hair is set in the desired shape, an oxidizing agent reforms the disulfide bonds in their new arrangement, locking in the change. The other bonds—hydrogen and salt bonds—are weaker and more easily altered by moisture and pH, so they contribute to temporary changes but don’t establish a permanent shape. Peptide bonds are the protein backbone and aren’t the targets of these chemical processes.