Which type of relaxer is classified as a lye product?

Sodium hydroxide is classified as a lye product, making it the correct answer. This type of relaxer is known for its strong alkaline properties, which facilitate the breaking down of the hair's disulfide bonds, thereby allowing the hair to be straightened. Sodium hydroxide relaxers provide quick and effective results, but they also require careful application to avoid damage to the hair and scalp due to their potency.

In contrast, while calcium hydroxide and guanidine hydroxide are also used in hair relaxers, they are not considered lye products in the traditional sense. Ammonium thioglycolate, on the other hand, is primarily used for permanent waving and is not typically classified as a relaxer that utilizes lye ingredients. Such distinctions are critical in the field of hair care, particularly in understanding the chemical composition and the resulting effects on hair texture.