“Does soap contain lye?” This is one of the most common questions asked, especially with the popularity of the term “no lye soap”. The surprising answer is No. Here’s why…
Soap does not contain lye. It is however, made by using lye. That’s an important distinction. You need lye to make soap. The finished soap product, however, no longer contains lye. The lye gets used up in the organic chemical reaction that makes soap; Saponification.
There might be leftover lye in a bar of unfinished soap-to-be, but that bar is not yet true soap. That’s the short answer. Here are answers to related questions I also wondered about when I got into soap making.
How can lye be used to make soap but not be in soap?
There is an organic chemical process called saponification that creates soap. Here’s how it works…
Lye and water (or other liquid) get mixed to form something called a lye solution. When fats and oils are exposed to the lye solution, they transform into soap by using it to fuel the conversion.
Like most fuels, lye gets used up on the journey or process. The result is a soap that can be used to clean the skin. It should have a pH of between 7 and 10 to be considered safe and ideal.
Is all the lye instantly gone?
No. It takes time for the saponification process to work. In cold process soap making, it normally takes 24 hours to 48 hours for all lye to be neutralized.
Can I speed up the saponification process in soap making?
You can accelerate saponification by making soap using the “hot process,” which uses nearly all the lye quickly. This is usually in about an hour or so – depending on batch size and temperature.
There are several variations of hot process soap making. You can use a steady heat source like a crockpot, baking dish in the oven, or stovetop. Or you can do something called countertop hot process. This uses the heat of the oils and lye solution to speed up the saponification process.
Technically all of the lye should be used up when the soap is done cooking. However, I still like to let it set for a day or so, after cutting the batch loaf into bars. This ensures ALL the lye gets used up.
That’s the great thing about saponification. As an organic chemical process, there is no outside heat source needed to “cook out” the lye. This is – because it is not really cooked at all, it is transmuted. I know that sounds like a Harry Potter thing, but it’s real. It is just the official way to say the chemical process changed the core ingredients.
The more common, cold process soaping method does not use any outside heat source at all. The saponification normally takes 24 to 48 hours to complete.
Even after the lye is used up, the water can still take weeks or months to fully evaporate. The absence of liquid is what makes a firm bar of soap.
But what if there is still lye in the bar?
If your soap has been sitting for several days and the pH level is too high (over 10 for example), there is likely unused lye in the soap.
This is called “free lye”. It usually means there was not enough fat or oil to use up all the lye.
The best way I know of to fix this is through a process called rebatching. It’s easy to do and consists basically of…
- Grating or cutting up the soap into small bits
- Adding liquid (or in this case) any extra oils you left out of the original batch
- Melting it to a Vaseline like form in the microwave, a slow cooker or however you want
- Placing it in a mold
- Letting it sit for 6 to 12 hours, then cutting into bars
>>> The Inside Edge
The following link leads to a detailed set of instructions for rebatching. It will show you how to recoup hundreds of dollars in “scrap soap”.
How do I know if my soap has “free lye”?
There are several ways to tell if your soap-to-be has any extra lye just waiting to burn you (literally!) The two most reliable methods, however, are by testing with pH strips or using a pH meter. Test strips are far simpler and cheaper, but a well-calibrated pH meter can provide more pinpoint accurate results.
If this is new to you, I recommend starting with “universal pH strips” with a pH indication range of 1-14.
I personally like the product put out by “LabRat Supplies”. You can get them from Amazon and other retail outlets for $5 or $6 per 100 pack. Just be sure to either get:
- Plastic strips that measure 0-14
- or the paper strips that measure 1-14 pH levels
Some strips only measure from 4.5 to 9 because they are used for spa and hot tub testing.
Water has a neutral pH of 7. Lye has high pH of 14. Soap should have a pH between 7 and 10.
What are the pH levels of foods?
To give you an idea of what you want to see, here are the pH levels for everyday items. When looking at these consider that soap is being applied to, and absorbed by, the largest organ of your body – your skin.
How can I avoid having leftover lye?
Always be sure to run your soap recipe through a lye calculator so the calculations are right. The Handcrafted Soap and Cosmetics Guild has a free lye calculator that works very well. This will help you figure out how much lye and water you will need for your lye solution. That will be the liquid to saponify the combination of fats and oils in your recipe.
As added insurance, and just to provide a more enriching soap bar, I also tend to “superfat” my soap. This just means having extra fats and oils that do not saponify. By having a bit of extra oil in the soap you can enhance certain aspects and properties such as moisturization. This can also increase creaminess, lather type, and more.
You might see or hear soap described as “enriched with added avocado oil” or something similar. This is a good indicator that the soap has been superfatted (because of the word “added”).
CAUTION: The trick is to not overdo it. If you have a lot of unsaponified olive oil, for example, you might just be making an oil slick. Tubs are slippery enough with that.
Why is lye listed on the soap label?
The main reason most people assume soap contains lye is because it appears on soap labels. Soap makers (soapers), like me, list lye as an ingredient for full disclosure.
This is because labeling laws allow either the ingredients that went into making the soap – OR the final output. The final output is simply “soap” plus whatever was added for color, fragrance, exfoliate, etc.
I prefer to list ALL Ingredients that went into making the soap. This is so people know exactly what oils, fats, and butters were used. Because of this I also list the things that get used up in the soap making process. These include lye and water.
Why is Glycerin soap called “no lye soap”?
Glycerin soap, another term for melt and pour soap base, is often referred to as “lye free”. This is because it is sold as fully saponified soap to the soaper. This simply means the person making soap can:
- Melt the Glycerin soap base
- Add whatever colors, fragrances or exfoliates they want
- Pour it into a mold
This is all accomplished without ever having to come in contact with lye.
Where can I learn more about lye?
Uncle Sam over at the United States Food and Drug Administration has plenty of helpful information about lye. Swing on over it check it out.
Happy Soaping!