Putting a sodium hydroxide relaxer under a hair dryer may have which effect on hair protein structure?

• A. Will link together all protein groups
• B. Could turn into van der Waals forces
• C. Will increase the hair's amino acid content
• D. Could break the critical peptide bonds and destroy the protein structure

Answer: (D)

When hair is exposed to a strong alkali like sodium hydroxide combined with heat, the chemical conditions can cause hydrolysis of the protein backbone. Keratin in hair is built from long polypeptide chains held together by peptide (amide) bonds. Under high pH and elevated temperature, these bonds can break, tearing apart the chains and destroying the overall protein structure. This is why such harsh conditions can lead to irreversible damage, loss of strength, and increased breakage.

Relaxers do aim to disrupt disulfide bonds to reshape the hair, but the addition of heat in a strong base raises the risk of breaking peptide bonds as well. The other options don’t fit because linking together protein groups would require new covalent cross-links, van der Waals forces do not account for chemical destruction, and increasing amino acid content isn’t something that happens through this treatment.