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Get Nerdy With Me: All About Lye

One of the questions I receive most often is whether I make "lye soap". This can come as a positive or a negative. Some people see lye soap as superior, helping with ailments like poison ivy. Others see lye soap as potentially harmful. When it comes to lye in soap, there are two absolute truths: 

  • Soap cannot be made without lye.
  • Properly made soap has no lye left in it.

Let's break it down.

What is soap?

Soap, by definition, is saponified oils. Oils are made with fatty acids. To saponify those fatty acids, they must be mixed with a highly alkaline substance, or lye. When you are looking at a proper ingredient list, you may see lye listed as sodium hydroxide on hard soaps or potassium hydroxide on liquid soaps.

Isn't lye harmful?

Before saponification, yes. Lye by itself is caustic. That is why you will always see me wearing gloves in my videos when making soap. However, lye is not harmful when used properly. Did you know that pretzels are usually dipped in a lye solution prior to cooking? It gives them that shiny exterior.

Through the saponification process, the lye and oils go through a chemical change to become a new substance - soap. As long as the proper amount of lye was used, there is no lye left in the finished product, making it completely safe. Additionally, well-made soap should also have a superfat, making the soap not only safe, but soothing.

What is a superfat? 

While this phrase has been used to describe my lower half on a few occasions, it is actually a good thing when making soap. To explain, we need to do a little math.

Every oil has a saponification value. This value shows how many milligrams of lye are needed to saponify a gram of the oil. To make that simpler, let's use an example. Shea butter has a saponification value of .13. If I mix .13mg of sodium hydroxide lye with 1g of shea butter, it will become soap. There will be no shea butter or lye left at the end of the process.

If I want a superfat, I need to add less lye than necessary. In the shea butter example, I may use .13mg of sodium hydroxide and 1.2g of shea butter. That would mean that .13mg of lye and 1g of shea butter is saponified, but .2g of shea butter does not go through the saponification process. That .2g is left to condition the newly cleansed skin. All Bubbly Ducky soaps have a luxurious superfat that creates a lotion-like lather and helps to condition.

Why was I told that the soap I purchased from another brand was made without lye?

As we have already discussed, all soap is made using lye. That is an unavoidable fact. However, I do have some guesses as to why a soap-like product may be advertised as being made without lye.

One possibility is that the maker uses a premade base, otherwise known as "melt and pour", rather than making their soap batter from scratch. The premade base is made using lye and saponified prior to the maker purchasing it. The maker then melts it down, adds any color, fragrance, or additives, and pours it into a mold. Technically, the maker did not use lye but the soap was absolutely made with lye originally and that should be listed as an ingredient if they list their ingredients.

Another option is that the product is actually a detergent. While soap is saponified oils, detergents (like most body washes) can use any number of surfactants to cleanse, which is why their ingredient lists are usually pretty lengthy and hard to pronounce. However, they should not be called soap.

The simplest possibility is that the maker is confused about the term "lye". I have seen a few makers state that their soap is made with sodium hydroxide, not lye. These are one and the same.

In all three instances, the maker may not have any malicious intent. They are likely just confused. 

Sum It Up (Quick Facts)

To break it down, here's the key points.

  • Soap cannot be made without lye.
  • Soap that is made properly, using the correct amount of lye for the specific oils being used, does not have any lye left and should have a superfat.

I hope that helps clear up some confusion! If you have any questions, please don't hesitate to ask! You can leave a comment below or email me at



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