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You may have heard that lye is used to make handmade soap and wondered how it could possibly be safe to use such a caustic compound on your skin. The good news is that a finished, cured bar of soap contains no lye at all. This is because, while lye is a critical ingredient in the soap making process, the chemical reaction that makes soap entirely neutralizes the lye.

If this sounds unlikely to you, it might surprise you to know that you have something in your house right now that is the result of a similar process: ordinary table salt. In their separate states, sodium (a metal) and chlorine (a gas) are highly toxic. But once they’re chemically combined, they create a substance (NaCl) that is absolutely safe to eat.

Chemically speaking, soap is also a salt, one that is derived from a fatty acid. A salt is the byproduct of the chemical reaction between an acid and a base (alkali). In bar soap making, the acid comes from the fatty acids (triglycerides) that are present in oils or butters, and the base comes from lye (sodium hydroxide). This chemical reaction is called saponification.

Soap makers carefully choose the oils (acids) to impart the characteristics they want in the final soap. For example, some oils make a firmer soap, others make soaps that create lots of lather. In our soaps, we use only ethically-sourced, high-quality oils, like extra virgin cold-pressed olive oil, naturally refined shea butter, expeller-pressed food grade coconut oil, and expeller-pressed castor oil, and we choose the specific oils that will give use the qualities we want for each type of bar.

To make our soaps, we carefully mix lye with goat milk, and then combine the lye/milk mixture with the selected oils. As the base and acid mixtures combine, the chemical magic of saponification happens. During saponification, the triglycerides in the oils release glycerol molecules. This allows the fatty acids in the oils to combine directly with the hydroxide ions in the lye, and this is what makes soap. The released glycerol molecules turn into glycerin, which add more moisture and softness to the soap.

Once saponification is complete, you end up with three things: a salt (the soap), glycerin (which becomes part of the soap), and water. Any trace amounts of the alkali that remain after saponification entirely disappear within a couple of days. Excess water evaporates as the soap cures over the course of several weeks.

So, while lye on its own is highly caustic, the saponification process entirely neutralizes its dangerous characteristics. In fact, you can’t make real soap without lye. While you won’t see lye listed as an ingredient in a bar of handmade soap, lye’s chemical composition is critical to making the gentle, natural bar of soap you use every day.