Here’s the truth to fall back on. Soap is the result of a chemical reaction called saponification that occurs between lye and a type of molecule called a triglyceride (a fat or oil), where both substances are chemically transformed, creating soap and natural glycerin. Neither of the original ingredients exists anymore. All the lye – either sodium hydroxide for bar soap or potassium hydroxide for liquid soap – is consumed in the reaction.
So, while soap is made with lye, it doesn’t contain lye. Modern methods and measuring scales – as opposed to what was available to frontier women – allow soap makers to use the proper mixture of oils and lye, ensuring that all lye is consumed. In addition, many soap makers, some soap makers , add more oil than is required for the chemical reaction, further ensuring the neutralization of lye and adding to the soap’s moisturizing qualities. Including extra fats in the mixture is known as superfatting.