Understanding Saponification and the Myth of Lye in Handcrafted Soap
By Robson Aleixo
Soapmaking is both a time-honored craft and a fascinating science. At the core of this beautiful transformation from oils to a cleansing bar is a process called saponification. While this process involves lye, a substance that sounds intimidating, many people don’t realize that in properly made soap, there’s no lye left in the final product.
This article will explain saponification, clear up the myths about lye in soap, and provide reliable references for deeper learning.
What Is Saponification?
Saponification is the chemical reaction between a fat or oil and a strong base, usually sodium hydroxide (NaOH) for bar soap or potassium hydroxide (KOH) for liquid soap. When these ingredients are combined in the right proportions, the triglycerides in the fats break down and react with the lye, forming glycerin and soap—the salt of a fatty acid (McDaniel, 2020).
In chemical terms: Fat or Oil (triglyceride)+NaOH (lye) → Soap (sodium salt of fatty acid)+Glycerin
This reaction is exothermic, meaning it releases heat. When carefully managed by soapmakers, the end result is a safe, stable bar of soap that can gently cleanse the skin.
For a deeper breakdown of the chemical reaction, Wikipedia’s article on Saponification offers a clear explanation.
The Myth of Lye in Handcrafted Soap
A common misconception—especially among beginners or cautious consumers—is that handmade soap contains harsh or dangerous lye. This isn’t true for properly made soap. While lye is an essential ingredient in the process, it does not remain in the final product when measured and mixed correctly.
Lye is Essential, Not Evil
Every bar of real soap—natural or commercial—was made with lye. But once saponification is complete, there’s no lye left. If the soap is formulated with a slight excess of oil (a technique called superfatting), there’s even a little extra moisturizing oil in the final bar (Cavitch, 1995).
In other words: the lye gets used up. It does its job and disappears.
Soap Safety and Testing
Reputable soapmakers carefully calculate their lye-to-oil ratios, use tools like soap calculators, and conduct pH testing to ensure their soaps are skin-safe. Most cold process soaps cure for 4 to 6 weeks, allowing any excess water to evaporate and the bar to harden and stabilize fully.
According to experts at Soap Queen, a trusted soapmaking resource, properly cured handmade soaps typically fall between pH 8 and 10—which is considered mild and safe for most skin types.
Why the Myth Persists
The myth likely lingers for two reasons:
- The word “lye” sounds harsh and scary. It conjures up images of caustic burns and harsh chemicals.
- Some poorly made homemade soaps may be lye-heavy due to inaccurate measurements. This is why understanding the process and following correct formulations is essential.
But for soapmakers who follow tested recipes and allow for proper curing time, there’s no reason to fear lye. In fact, without it, you don’t have soap—just a mix of oils and water.
Final Thoughts
Handcrafted soap is a perfect blend of art and science. Through saponification, oils and lye come together to form a luxurious bar that’s both functional and beautiful. The key takeaway? When made correctly, no lye remains in the soap. So you can feel confident using—or making—handcrafted soap that’s as safe as it is nourishing.
References
- Cavitch, S. M. (1995). The Natural Soap Book: Making Herbal and Vegetable-Based Soaps. Storey Publishing.
- McDaniel, A. (2020). Soap Making 101: Beginner’s Guide to Cold Process Soap. Firefly Books.
- Wikipedia contributors. (2024). Saponification. In Wikipedia, The Free Encyclopedia. Retrieved from https://en.wikipedia.org/wiki/Saponification
- Soap Queen. (n.d.). Lye Safety Guide. Retrieved from https://www.soapqueen.com/bath-and-body-tutorials/cold-process-soap/lye-safety-guide/