Sodium Hydroxide
Sodium hydroxide, commonly known as lye, is a solid white, highly alkaline substance. It is used in small amounts in cosmetic formulations primarily to adjust and balance the pH of a product. It appears frequently in soaps, cleansers, and exfoliants, and has historically been used in soap-making by reacting with oils and fats. Its official CosIng functions are listed as buffering and denaturant.
Sodium hydroxide itself does not provide direct skin benefits, but it plays a critical role in ensuring products such as AHA/BHA exfoliants are formulated at the correct pH for efficacy. Once it has reacted within a formulation, it is considered harmless to the skin.
Sodium hydroxide in its unreacted form is a potent skin irritant. However, as used in finished cosmetic products where it has fully reacted, it is considered safe. Care should be taken with products where it may not be fully neutralized.
