Final answer:
Ammonium thioglycolate (ATG) is the active ingredient in acid waves, which are used to perm hair by breaking and reshaping the disulfide bonds.
Step-by-step explanation:
The active ingredient in acid waves is ammonium thioglycolate (ATG). Acid waves, also referred to as perms, use this chemical to break the disulfide bonds in hair. These bonds are responsible for the hair's natural shape, and once broken, hair can be reshaped to form curls or waves. After the hair is reshaped, another chemical, typically a neutralizer, is used to reform the disulfide bonds and lock in the new shape.