A leading depilatory chemical manufactur in Japan Developed Thioglycolic Acid (TGA) as the active material in permanent cold waves also called hair perms.The reducing capacity of the SH-group breaks up sulfur bridges in the hair structure and in a second oxidizing reaction the sulfur bridges are linked again after the hair was brought into its new shape. Consequently later the development of hair straighteners followed.
But TGA and some of its salts are also used in depilatories to remove hair from the skin.