Massachusetts Board of Cosmetology Practice Exam 2026 - Free Cosmetology Practice Questions and Study Guide

Sodium hydroxide is commonly used in hair straightening treatments due to its strong alkaline properties that enable it to break down the protein structure of the hair. This chemical is often found in lye-based relaxers, which work effectively to straighten tightly curled or textured hair. By altering the hair's structure, sodium hydroxide allows the curls to be loosened or completely straightened, resulting in smoother, more manageable hair.

In contrast, while hydrogen peroxide is a bleaching agent that can lighten hair, it is not used specifically for straightening. Ammonium thioglycolate is actually utilized in perm solutions and can also be used for some straightening methods but is not as frequently associated with traditional chemical straightening as sodium hydroxide. Glycerin, on the other hand, is primarily used as a humectant and moisturizer in hair products and is not involved in chemically altering the hair's structure for straightening purposes. This reinforces sodium hydroxide's significance in the realm of hair straightening treatments.