Final answer:
The active ingredient in alkaline permanent waves is ammonium thioglycolate, which disrupts disulfide bonds in hair.
Step-by-step explanation:
The active ingredient or reducing agent in alkaline permanent waves is ammonium thioglycolate. This chemical is used to reduce and rupture some of the disulfide cross-links in the hair during the permanent wave process. As explained in Figure 21.6.12, the disulfide bonds in hair are crucial for hair strength and structure. By applying ammonium thioglycolate, these bonds are temporarily broken, allowing hair to be reformed around rollers or curlers. Later, an oxidizing agent such as hydrogen peroxide is applied to reform the disulfide bonds in their new positions, fixing the hair into its new shape.