Traditional soaps have long been made by mixing oils (animal fats or vegetable oils) and liquid (most often water) with an alkali. The alkali works on the oils and triggers a chemical process called saponification. Saponification is the act of turning oils, liquid, and alkali into soap.
For making bar soap the alkali used is sodium hydroxide, also known as lye. Although this sounds harsh (who wants to wash with lye?) there is no lye left in properly made soap. All of the ingredients have been converted into soap.
Historically, soap was made with tallow (beef fat) or lard (pork fat). Soap makers today still make soap in the same manner, except modern soaps are more likely to contain coconut oil, palm oil, olive oil, and other specialty fruit, nut, and/or vegetable oils than animal fats. Manufacturers also add fragrance, colors, essential oils, herbs, and other ingredients to add the product’s appeal, although many of these add-ins do little in the way of contributing to good skin health.