What chemical is commonly used for permanent waving?

Ammonium thioglycolate is commonly used for permanent waving because it serves as a reducing agent that breaks the disulfide bonds in the hair's protein structure (keratin). This process allows the hair to be reshaped when wrapped around a perm rod. Once the hair is set in the desired curl pattern and the solution has processed, a neutralizing solution is applied to reform the disulfide bonds in their new configuration, resulting in a long-lasting wave or curl.

Sodium hydroxide, while also used in some chemical processing, primarily serves as a relaxer for straightening hair rather than creating waves. Glycerin is a moisturizing agent and does not have the chemical properties necessary for altering the hair's structure in the way that permanent waving requires. Hydrogen peroxide is commonly used as a bleaching agent or in hair color processes, but it does not contribute to the wave formation needed for a permanent wave service.