Disulfide bonds are stronger than hydrogen and salt bonds; which statement is true?

• A. They are weaker than hydrogen bonds
• B. They are unaffected by chemical treatments
• C. They are stronger than hydrogen and salt bonds
• D. They are only found in the cortex

Answer: (C)

Disulfide bonds are covalent links between sulfur atoms on cysteine residues in hair keratin, creating strong cross-links that help lock in the hair’s shape. Because they’re covalent, these bonds are far more robust than hydrogen bonds or salt (ionic) bonds, making them the primary contributors to hair strength and permanent shape. Hydrogen bonds are weak and readily break with moisture and heat, while salt bonds are ionic and easily disrupted by pH changes; both are far less durable than disulfide bonds.

Chemical treatments target these bonds: reducing agents break disulfide bonds so the hair can be reshaped, and then an oxidizing agent reforms them in the new configuration, which is how perms and relaxers create lasting changes. That’s why the statement identifying disulfide bonds as stronger than hydrogen and salt bonds is true. The other options don’t fit because disulfide bonds are not immune to chemical treatments, they are not simply weaker than hydrogen bonds, and their presence is not limited to the cortex in a way that would support the stated claim.