California Cosmetology Practice Exam

Ammonium thioglycolate is commonly used for permanent waving because it serves as a reducing agent that alters the structure of the hair. When applied, it breaks the disulfide bonds in the hair's keratin proteins. This process allows the hair to be reshaped and set into a new curl pattern when wrapped around rods. The effectiveness of ammonium thioglycolate lies in its ability to create long-lasting curls and waves, making it a staple in the permanent waving process.

Hydrogen peroxide is primarily used as a bleaching agent rather than for waving, working more to oxidize color in hair than to change its texture. Cetyl alcohol serves as an emulsifier and conditioning agent, not as a waving solution. Sodium hydroxide is used in chemical relaxers to straighten hair by breaking down the proteins, which is contrary to the intention of a perm, as it would not create curls or waves. Thus, ammonium thioglycolate is distinctly suited for this purpose, making it the correct answer.