Which bond type in hair involves sulfur atoms and contributes to hair's strength?

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

Answer: (C)

Disulfide bonds are the bonds that involve sulfur atoms in hair. They form covalent cross-links between cysteine amino acids in keratin, linking strands and segments of the protein to create strong, stable structure. This cross-linking is what gives hair much of its strength and shape, making it resistant to basic washing and heat. When chemical processes like perms or relaxers use reducing agents, these bonds can be broken and later re-formed through oxidation, which is why such treatments can permanently alter texture. Other bonds in hair, like hydrogen bonds or ionic bonds, are weaker and more easily disrupted by moisture or pH changes, while peptide bonds connect amino acids in the protein backbone but don’t provide the same cross-link strength. So the sulfur-containing cross-links that lock keratin fibers together are the disulfide bonds responsible for hair’s strength.