Iowa Cosmetology Practice Exam 2025 - Free Cosmetology Practice Questions and Study Guide

Sodium hydroxide is a powerful alkaline chemical commonly used in hair straightening treatments, particularly in the form of relaxers. It works by breaking down the disulfide bonds in the hair’s protein structure, allowing the hair to be reshaped and straightened. This process is especially effective for those with very curly or textured hair, as it can provide a long-lasting straightening effect.

The other chemicals mentioned have different uses in hair treatment. Hydrogen peroxide is typically used as a bleaching agent and can lighten hair color, but it does not alter the structure for straightening. Ammonium thioglycolate is also used in chemical hair treatments, specifically for perming and in some relaxers, but sodium hydroxide is more commonly associated with traditional hair straightening. Glycolic acid is primarily used for skin care and does not play a direct role in hair straightening. Therefore, sodium hydroxide stands out as the chemical specifically designed for the purpose of hair straightening.