Let's start with a little basic chemistry. The chemical reaction that produces soap is called saponification. To cause saponification, we react oils or butters with sodium hydroxide (NaOH). Saponification literally means "turning into soap" from the root word, "sapo", which is Latin for soap. After saponification is complete, No Lye Remains. Vegetable fats are triglycerides, which are made up of a glycerol and three fatty acids. When you combine them with a strong base like sodium hydroxide, they break up into sodium salts of fatty acids—that’s the soap!—and glycerin. Glycerin is also very useful because it’s a humectant, meaning that it helps your skin maintain hydration by capturing water molecules from the air and retaining them on your skin.