Which perm type uses cysteine hydrochloride as the reducing agent?

• A. Acid perms
• B. Alkaline perms
• C. Exothermic perms
• D. Low/no Thio perms

Answer: (D)

The key idea here is that the reducing agent used in a perm defines the perm type. Cysteine hydrochloride is an amino acid–based reducing agent used in low/ no-thiol perms. This milder reducing agent breaks the disulfide bonds in the hair to allow reshaping, but does so with different chemistry than the thioglycolate-based systems. That’s why this perm type is categorized as low/no thio. After the hair is reformed on the rods, a neutralizer re-forms the disulfide bonds in the new configuration.

The other perm types rely on thioglycolate-based reducing agents (found in alkaline and acid perms) or are described by the heat/processing approach (exothermic) rather than by using cysteine hydrochloride.