Why Do We Use Lye In Soap?

Understand the use of and safety risks associated with lye to ensure you have an effortless and enjoyable soap-making experience.

by Jan Berry
Why Use Lye In Soap? - Photo courtesy Jan Berry (HobbyFarms.com)
Courtesy Jan Berry

In times past, our grandmothers made their own lye, called potash, using wood ashes and water. They would combine it with fat rendered from butchered animals and boil the mixture over an outdoor fire for many hours until a soft soap was formed. While this was a natural and admirable way to make soap, it was also labor-intensive and difficult to control the quality of the final product.

Modern times have brought about man-made substitutes to replace the wood-ash solution. Sodium hydroxide (also called caustic soda or lye) is commonly used to create solid bars of soap, while potassium hydroxide is used to make liquid soap. With these standardized ingredients, the guesswork has been removed and soap crafters can reliably produce batch after batch of gentle, balanced soap.

Many people are interested in making their own soap but find the idea of handling lye intimidating. Words like “sodium hydroxide” sound far from natural, and the warnings that accompany this substance are downright scary. While there are legitimate concerns and misconceptions about using lye, by practicing safe handling or substituting it with another ingredient, you can safely and confidently produce soap at home. 

Can You Make Soap Without Lye?

Why Use Lye In Soap? - Photo courtesy Jan Berry (HobbyFarms.com)
Courtesy Jan Berry

The short answer to this question is no. By definition, soap is what you end up with when fats and oils are combined with a caustic solution (lye).  

When lye comes in contact with oils, a chemical reaction occurs that changes both substances. Once that reaction is complete, you no longer have fat or lye—you have created soap.

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Even most store-bought soaps are made with lye. Look at the label of your favorite bar of commercially made soap, and you’ll likely find words like sodium cocoate or sodium tallowate. That’s just a fancy way of naming coconut oil or tallow that has been reacted with sodium hydroxide (lye). Sometimes, you might spot soaps that are labeled with ingredients such as “saponified olive oil” or “saponified coconut oil.” Saponified is just another word used to describe fats or oils that have been turned into soap, using lye.

The bars that don’t use lye rely upon a hodgepodge of synthetic detergents, such as sodium laureth sulfate, to produce suds and are not considered true soaps. A main difference found in store-bought soaps is that the big companies have devised methods to separate out glycerin, a natural byproduct of soap-making, and sell it separately. In soap made from scratch, the glycerin is naturally distributed throughout the bar. For this reason, homemade soaps tend to be more moisturizing.

It’s important to note that no matter who makes the soap, there is no lye left in the final product. It’s all “used up” and transformed on a molecular level during the process of converting the oils into soap.

Lye Safety Tips
If you decide to venture into soap-making, follow safety precautions to help reduce the risk of serious harm. While lye can be dangerous if handled improperly, you will rarely encounter issues if you work in a thoughtful and careful manner.

  • Handle lye responsibly. Lye should be used only by responsible adults. Never use it around children or pets.
  • Wear safety goggles, long sleeves and gloves during soap-making sessions. Lye solution and fresh soap batter can cause serious and permanent damage to your eyes and painful chemical burns on your skin. If this happens, rinse repeatedly with generous amounts of cold water for several minutes. Seek medical attention promptly for eye contact and large burns.
  • Always pour lye into water that is room temperature or colder. By adding water to dry lye or pouring lye into hot water you risk overheating and producing a volcano effect. For this reason, it’s also a good idea to mix lye in your kitchen sink. If any accidents occur, they will be contained and easier to clean up than a countertop spill.
  • Avoid breathing in fumes. When lye is first mixed with water, it will form strong fumes. Work in a well-ventilated area and turn your head away as you stir. If you find yourself sensitive to the fumes, consider wearing a face mask.
  • Clearly label lye-solution containers with a skull and crossbones symbol. By doing this, even non-readers will realize it’s dangerous. Like many strong household chemicals, lye can be fatal if accidentally swallowed.
  • Using the proper equipment. Pans should be stainless steel or enamel. Never use aluminum when making soap, as it will combine with lye to form a dangerous chemical reaction. Mix your lye solution in a heat-proof plastic container, as glass has the potential to shatter.

Remember that these are worst-case scenarios. Soap is made every day by many people without incident. Caution when handling is wise and necessary, but don’t allow fear to keep you from trying out a rewarding new pastime.

Lye Substitutes

Why Use Lye In Soap? - Photo courtesy Jan Berry (HobbyFarms.com)
Courtesy Jan Berry

It’s perfectly OK if you decide that the risks of handling lye outweigh the benefits. Not everyone has the desire or means to make soap from scratch. You can always seek out local soap makers and support their family businesses or experiment with other soap or soap-like options.

A popular alternative to lye soap is using a melt and pour soap base, sometimes called glycerin soap. It can be found online and in some craft stores. While it contains lye, the manufacturer has pre-handled it. You simply melt the base, stir in the colors and scents that you like, and pour it into molds. The benefit is that it’s safe enough for children to make with supervision and ready to use almost right away. The main drawback is that these bases are sometimes loaded with ingredients that are far from natural and virtually all contain palm oil, which is fraught with sustainability issues. Read labels carefully.

Plants high in natural substances called saponins offer lye-free cleansing with varying amounts of effectiveness. These include yucca, soap nuts and the herb soapwort. When using these products, keep in mind that most saponins are highly toxic to fish, so avoid growing or using these plants near a water source.

To make shampoo, body cleanser, dish soap and more with these plants, you’ll need to do a little prep work.

  • Soap nuts: Simmer 5 or 6 nuts in 1½ cups water in a covered pan for about 1 hour. Mash the softened hulls with a fork to release the saponins into the water. Cool completely and then strain.
  • Soapwort: Chop a handful of leaves and simmer in 1 cup water for 10 to 15 minutes. Cool before straining.
  • Yucca: Mix leaves with water, without heating.

You’ll find that these cleansing mixtures are watery and won’t lather the same way regular soap and shampoo do, though they can sting your eyes in a similar manner. If swallowed, saponins can make you quite ill. Be sure to clearly mark containers so no one confuses them with beverages. Because they’re water-based and don’t contain preservatives, the shelf life can only be numbered in days. Freeze small amounts in ice-cube trays for future individual uses.

As you can see, whether you make your own soap with lye, or use an alternative, you’ll encounter both advantages and disadvantages. There is no one perfect solution, but being informed of all the possibilities will help you decide the best option for you and your family.

Get these soap-making recipes and tips from HobbyFarms.com:

About the Author: Jan Berry lives on a small hobby farm in the Blue Ridge mountains of Virginia with her husband, two children and assorted collection of goats, ducks, chickens, bunnies, dogs and one cat—aptly named Rascal. You can find her online at www.thenerdyfarmwife.com.


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