Purpose: To investigate efficacy of a low-viscosity thioglycolate-based permanent wave technique on hair repeatedly damaged by cysteamine-HCl treatment and to hair-protective effects.Methods: Hair damage was induced using a cysteamine-HCl solution prior to permanent waving. In the control group, the hair was treated with a thioglycolate-based cream-type reducing agent (pH 8.9) for 15 min. The experimental groups received the same reducing agent for 10 min, followed by an additional low-viscosity, gel-type permanent solution at pH 4.5, 7, or 9 for 5 min to achieve a double-softening effect. Wave efficiency, hair diameter, tensile strength, elastic modulus, and hair damage were assessed, and hair surface morphology was examined by scanning electron microscopy (SEM).Results: The experimental group treated with the additional gel-type reducing agent at pH 4.5 showed significantly greater hair diameter, tensile strength, and elastic modulus, along with the lowest level of hair damage among the groups. The group treated with the additional gel-type reducing agent at pH 7 demonstrated significantly greater wave efficiency, tensile strength, and elastic modulus. SEM observations in all groups revealed structural damage to the cuticle caused by repeated chemical treatments.Conclusion: For hair repeatedly damaged by cysteamine-HCl treatment, a permanent waving strategy using an additional gel-type reducing agent at pH 7 is optimal for enhancing wave efficiency and elasticity, whereas the same strategy at pH 4.5 is more effective for minimizing hair damage and improving hair protection.
Lee et al. (Thu,) studied this question.