New York State Barber Practice Exam

Sodium hydroxide is the primary ingredient in most hair relaxers due to its strong alkaline properties, which effectively break down the disulfide bonds in the hair's keratin structure. These disulfide bonds are responsible for the hair's natural curl pattern, and by breaking them, sodium hydroxide facilitates the straightening process. This compound is particularly effective for those with tightly curled or coarse hair, allowing for smoother, more manageable results.

Sodium hydroxide is often referred to as "lye" and is known for delivering powerful results in hair relaxation treatments. It's important for practitioners to use it correctly to avoid potential damage to the hair and scalp, as it can be very caustic if misapplied. This quality makes sodium hydroxide a staple in chemical hair relaxing products in the beauty industry.

The other options, while they may have various uses in hair and cosmetic products, do not serve the same primary function as sodium hydroxide in hair relaxers. Sodium bicarbonate is more commonly associated with gentler, pH-balancing products, calcium sulfate is often used in hair treatments for different purposes, and potassium chloride is known for its use in salt substitutes and certain conditioning agents, but none are primarily used for relaxing hair.