What chemical solution is commonly used in permanent wave services?

The commonly used chemical solution in permanent wave services is thioglycolic acid. This compound is essential in the process because it serves as a reducing agent that breaks down the disulfide bonds in the hair. This allows the hair to be reshaped into curls or waves when it's wrapped around perm rods.

Thioglycolic acid has the ability to penetrate the hair shaft, and when mixed with a solution, it creates a reaction that alters the hair's structure. The effectiveness of thioglycolic acid in reshaping hair makes it indispensable in the permanent waving process, contributing to the longevity of the style.

In contrast, while ammonia is often used as a part of the permanent wave solution to help open the hair cuticle, it is not the key chemical in creating the curl. Similarly, hydrogen peroxide is typically involved in hair coloring rather than permanent waving, and alcohol does not play a role in the chemical restructuring of hair for permanent waves. Thus, thioglycolic acid is accurately identified as the primary chemical used in this hair service.