The main active ingredient or reducing agent in alkaline permanent waves is

• A. Ammonium thioglycolate
• B. Sodium bisulfite
• C. Calcium carbonate
• D. Sodium hydroxide

Answer: (A)

The thing being tested is how alkaline permanent waving works at the chemical level: a reducing agent is needed to break the hair’s disulfide bonds so it can be reshaped around a rod. In alkaline waves, the active reducing agent is ammonium thioglycolate, the ammonium salt form of thioglycolic acid. It donates electrons to cleave the disulfide bonds in the keratin, converting them into more flexible thiol groups so the hair can be reformed in the desired curl pattern. After the hair is positioned, a neutralizer—usually hydrogen peroxide—oxidizes those thiol groups back into disulfide bonds, locking in the new shape. The other substances listed aren’t the primary reducing agent in this system: sodium bisulfite is not used as the main reducer in standard alkaline waves, and calcium carbonate and sodium hydroxide are bases used to adjust pH rather than to reduce disulfide bonds.