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

Sodium hydroxide is commonly used in relaxers for straightening hair because it is a powerful alkaline ingredient that works by breaking down the protein structure of the hair. This process allows the hair to be reshaped into a straighter form. The high pH level of sodium hydroxide opens the hair cuticle and penetrates the cortex, effectively loosening the bonds that hold the hair in its natural curl pattern.

The efficacy of sodium hydroxide in hair straightening makes it a popular choice in many chemical relaxers used within the cosmetology industry. It is crucial, however, to use this ingredient with caution due to its caustic nature and potential to cause irritation or damage if not applied correctly or if used on hair that has been previously treated with other chemicals.

Other ingredients like hydrogen peroxide are typically associated with bleaching or lightening hair rather than straightening it, while coconut oil and dimethicone are used for conditioning and smoothing, but do not possess the chemical properties needed for relaxing textured hair.