Sodium Hydroxide Average pH-adjuster-stabiliser No known benefits Sodium Hydroxide at a glance Highly alkaline ingredient Used in small amounts in cosmetics (such as in exfoliants and cleansers) to adjust pH Is used in hair and nail products to maintain pH Also known as lye Sodium Hydroxide description Sodium hydroxide, also known as lye, is a highly alkaline (also known as “basic”) ingredient used in small amounts in cosmetics to establish and hold the pH of a product in an acidic or alkaline formula. This is seen particularly in products such as cleansers and in leave-on exfoliants, where the product’s pH needs to be held within a very specific range for maximum efficacy (between 3-4 is ideal for acid-based exfoliants, while cleansers are generally pH 4.5-6). Pure sodium hydroxide’s pH level is 13, but in cosmetics, it is only used up to pH 11. Sodium hydroxide is seen in many applications in beauty products, such as nail cuticle solvents and hair straighteners, where it’s used in greater amounts (between 2% and 5% concentrations by weight) than in leave-on skin care products or makeup (for example, some lipsticks contain 0.25% sodium hydroxide). It’s also used as a cleansing and denaturing agent. It’s a significant skin sensitizer in concentrations of 10% or greater.