What structure must be permanently broken to change the hair from straight to curly?

What structure must be permanently broken to change the hair from straight to curly?

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

Answer: (C)

Disulfide bonds. These covalent links between sulfur atoms in cysteine residues within the hair’s keratin cross-link the cortex and largely determine the hair’s shape. In a perm, a reducing agent breaks these disulfide bonds, letting the hair be reshaped around rods. Then an oxidizing step reforms new disulfide bonds in the curl pattern, locking in the permanent shape. Hydrogen bonds and salt bonds are weaker and break with moisture or pH changes, so they only allow temporary changes and reform when conditions return to normal. Peptide bonds hold the protein together but aren’t the bonds you alter to permanently change hair texture without damaging it.

Disulfide bonds. These covalent links between sulfur atoms in cysteine residues within the hair’s keratin cross-link the cortex and largely determine the hair’s shape. In a perm, a reducing agent breaks these disulfide bonds, letting the hair be reshaped around rods. Then an oxidizing step reforms new disulfide bonds in the curl pattern, locking in the permanent shape. Hydrogen bonds and salt bonds are weaker and break with moisture or pH changes, so they only allow temporary changes and reform when conditions return to normal. Peptide bonds hold the protein together but aren’t the bonds you alter to permanently change hair texture without damaging it.