North Dakota Cosmetology Practice Exam

Sodium hydroxide is a key ingredient in many hair relaxers due to its powerful alkaline properties, which help to break the disulfide bonds in the hair's protein structure. This process allows the hair to be reshaped and becomes straightened. Sodium hydroxide is effective at altering the hair's pH, facilitating the relaxing effect on curly or wavy hair textures.

The other choices do not have the same primary function in hair relaxers. Calcium carbonate, for example, is typically not used as a relaxer ingredient but may be found in other formulations, such as shampoos or conditioners for its mild abrasiveness. Ammonium thioglycolate is primarily used in permanent waving and curling products rather than relaxing. Alcohol denat serves as a solvent in many cosmetic products but does not contribute to the chemical restructuring of hair fibers. Therefore, sodium hydroxide stands out as the most critical component for effectively relaxing hair.