Sodium Hydroxide, also known as caustic soda, is one of the strongest alkali bases used for pH balance control in skin and hair care applications. However, caustic soda may bring chemical burns, it can't be used individually, and it is used only with acids in formula to increase (balance) pH as an alkalizing agent.
Thanks to its complex forming ability with some inorganic colored compounds (such as iron oxide and titanium dioxide), Sodium Hydroxide is also used in pigments as a stabilizer in decorative cosmetics. It can soften hard water and improve the effectiveness of surfactants in cleansing preparations.
In addition, caustic soda is used as a relaxer for straightening very curled hair in some hair care formulas.