What is thioglycolic acid commonly used for in cosmetology?

Thioglycolic acid is primarily recognized in cosmetology for its role as a reducing agent. It is widely used in chemical wave solutions and perming products due to its ability to break down the disulfide bonds in the hair’s keratin structure. This process allows the hair to be reshaped into curls or waves. The effectiveness of thioglycolic acid in altering the internal structure of hair makes it invaluable in both permanent wave treatments and relaxers.

In contrast, the other choices indicate different functions that thioglycolic acid does not fulfill. For example, as a color additive, it is not meant for adding pigment to hair, which typically involves dyes or other coloring agents. Similarly, as a conditioning agent or a thickening agent, these roles are fulfilled by different compounds specifically formulated for moisturizing or altering the viscosity of products, rather than through thioglycolic acid. Thus, its primary classification and function as a reducing agent underline its significance in various hair treatments within cosmetology.