Lye is used in the making of solid and liquid soaps, as such it may appear on ingredient lists for soap bars, handwashes, castile soaps, and any other cleaning products which don’t make use of chemical detergents.

The various lyes used in commercial products are made by oxidation of sodium or potassium.

Sodium Hydroxide and Potassium Hydroxide are listed in the Cosmetics Directive of the European Union and may be used at the following concentrations and pH values: 5% by weight in nail cuticle solvents, 2% by weight in hair straighteners for general use, 4.5% by weight in hair straighteners for professional (salon) use, up to a pH 12.7 in hair removal products, and up to pH 11 in other uses as a pH adjuster.

Professional soap makers are careful to ensure that their final product’s pH does not exceed 9-10. If the soap is more basic than this, it can irritate the skin.

Lyes fully react with oils, when the correct balance or a superfat percentage is used, and none remains present in a carefully produced soap product.