The Truth About Lye and Soap

Banner featuring man washing hands with bubbly soap and the overlay text "Why would anyone want to use something as caustic as lye on their skin?"

We had a customer ask us the other day, “Why would anyone want to use something as caustic as lye on their skin?” We also had a guy on the phone comment, “Lye doesn’t seem very organic, man.” And by “organic,” he meant groovy.

On the organic point, he was right. Lye isn’t organic, but it is one of the allowable non-organic ingredients included in USDA organic standards since their inception. On the groovy point, we disagree. The truth about lye in soap-making is simple: there is no true soap, as defined by the FDA, without lye. There’s also a huge difference between “made with lye” and “containing lye.”

None of this is news to people in the soap business. For the public at large, though, and even for some soap-makers, the subject can be confusing. Lye, after all, is also known as caustic soda, and soap made from lye is what frontier women made in cauldrons that was great on clothes but murder on skin.

Many perceptions of lye have nothing to do with modern soap-making. But if you’re in the business of making or selling soap, these perceptions persist and are part of your life. The good news is you can always fall back on chemistry, which is where the truth lies. You’re not using lye on your skin. You’re using soap.


The Chemistry of Soap

Here’s the truth to fall back on: soap is the result of a chemical reaction called saponification that occurs between lye and a type of molecule called a triglyceride (a fat or oil), where both substances are chemically transformed, creating soap and natural glycerin. Neither of the original ingredients exists anymore. All the lye – either sodium hydroxide for bar soap or potassium hydroxide for liquid soap – is consumed in the reaction.

So, while soap is made with lye, it doesn’t contain lye. Modern methods and measuring scales – as opposed to what was available to frontier women – allow soap-makers to use the proper mixture of oils and lye, ensuring that all lye is consumed. In addition, many soap-makers, including Botanie Soap, add more oil than is required for the chemical reaction, further ensuring the neutralization of lye and adding to the soap’s moisturizing qualities. Including extra fats in the mixture is known as superfatting.


Lye “Alternatives”

Still, some soap-makers make a point of positioning themselves as lye “alternatives,” insisting – for example – they use glycerin instead, or make their soap without the involvement of lye. In both these cases, misinformation seems to be a factor. Glycerin is a natural result of saponification. And the first step in creating bases for melt-and-pour soap-making – the most convenient home-based process? Saponification.


Bars of organic, colorful soap by Botanie are lined up during production, almost ready to ship in bulk.


Changing the Perceptions of Soap

Understanding chemistry can go a long way toward informing public perceptions, including those of your customers. As negative as some perceptions of lye can be, all soap is made with lye – whether it’s bar or liquid – and soap made well can be great for your skin. The distinction between soap and commercial cleansers is especially clear with liquid soaps. Since most weren’t made with lye, what you’re buying isn’t soap, but a factory-made detergent for the skin.

Perceptions have their own momentum, and they can cause consumers to avoid products they might otherwise use. But perceptions can also be changed. Lye isn’t a villain, nor is soap made with lye something to avoid. In fact, in the hands of good soap-makers, it’s a product made with your skin and health in mind, and is far superior in overall quality and gentleness to commercial, non-soap cleansers. Lye is what you should be using.



13 thoughts on “The Truth About Lye and Soap

  1. i own my own company and we are going to start creating our own soap for retail along with our other products, is there a website or anything that could give me the basics, such as ingredients, procedure, production precedures, curing proceedures?

  2. Hi there,
    i do a small handcrafted soap social enterprise based in Kalimantan, Indonesia.

    When i write up the ingredient i include ‘sodium hydroxide’ as an ingredient. As such is that correct or not? For example:
    ” Ingredients: Home harvested coconut oil, distilled lemongrass water, organic aloe vera, sodium hydroxide, scented with Lavender & Tea Tree essential oil, and organic moringa powder set in a banana leaf compostable lining.”

    As an international soap making standard would you say this is this correct? or should i write lye (instead of sodium hydroxide) or should i omit both lye and sodium hydroxide as it disappears in the curing process?

    Many thanks in advance and thanks for a fantastic article..


    • There is very good all-natural soap you can buy here (Dr. Bronner’s) that lists sodium hydroxide in the ingredients with a sign (*) indicating a footnote. You look below at the note and it says something like, *”Not present in soap, disappears in soapmaking process.” This is precisely correct. I recommend doing that. Then the user knows it is true soap, which requires lye ( sodium hydroxide) to make but does not contain lye after the chemistry of saponification occurs .

      • Thank you Dr Rose, what you wrote is very interesting, I feel better about making and selling my ‘natural handmade shampoo bars and soaps’ at the local farmers market! I feel More confident and better educated to answer questions about the ingredients I use!
        Blessings Susan ( from Ireland)

      • Hi Britta,
        I have been researching soaps as I found out that one should NOT be using any toothpastes on the market, especially those with periodontal disease, teeth lose, gums receding, apses etc.etc. A scientist/dentist from many years back stated the cure of remineralising teeth is to buy a bar of soap!! And put your brush on the soap and clean your teeth with it and all your problems will go. Concerning the Bronner soap this is available on Amazon and they also sell other soaps by a few other sellers, organic and pure no this that or the other but yes LYE was in the soaps, hence my checking this out. This has given me a bit of peace and mind. I was researching on a very large forum under painful gums teeth losing etc.etc. and yes! They are being told get rid of your toothpastes! Use soap on your teeth and gums and they will start to get better, so yes, I am researching. A few suggested Dr. Bronner soap, but of course, I too, was worried about Lye in it, but the article has put my mind at rest. But still uncertain about using Bronnr soap on my teeth and gums? Need to check out further, but providing it doesn’t have glycerine which it doesn’t from another seller, this might be what I am looking, but yes to your question Britta you should be able to buy it because I am sue Amazon would supply to Ireland. Hope this is of help. Rosina Lock x

        • I have a had a brick and mortar soap business in Connecticut USA for over 5 years and have made tons of different kind of soaps. First, there is no lye at all in cold process soap. The lye is a catalyst which turn the fats (I use olive oil, coconut oil, palm old, canola oil and castor oil in all my soaps) into a solid bar of soap If you didn’t have the lye, you would just have a bucket of greasy oil. I would not recommend brushing your teeth with soap. I do know that Coconut Oil, when gargled and swished around in the mouth, is thought to mineralize the teeth and stop or reverse decay. I am not a dentist and don’t know if this is true or not. You say you are worried about the glycerin. If the soap is real cold process soap, then it pretty much is ALL glycerin When cooking soap in a crockpot (called hot process soap) within about one hour or cooking the ENTIRE BATCH of soap turn to GLYCERIN. It looks like a tan, jelly like substance. One this occurs, you know the soap is done and ready to add your fragrance to and put in the molds. Commercial “soap’ makers (not real soap), remove the glycerin that floats atop of the finished soap and sell it. This is why commercial bar soaps leave your skin dry and itchy. Dr Bronner is a popular organic real soap and if you cannot find any other real cold process soap where you live, this is what you want. Be careful when shopping on Amazon or Etsy as so many sellers say their soaps are made from scratch, and they are not, but rather a soap base that they melt and add additives to. Try using a bit of baking soda, bentonite or kaolin clay and activated charcoal on your teeth – just don’t swallow. You will be surprised at how clean your teeth will feel. Add a couple drops of mint or cinnamon oil if you don’t like the taste. Hope this answers some of your questions. – Cindy of Connecticut Soap Co, LLC d/b/a Cindy’s Soap Cottage

  3. What do I need to put in my soap that will make it stay fresh longer. Is it a preservative? After a while my soap doesn’t smell as great. Still washes good!

    • Hi, Sharon – Thanks for the question. We definitely know what you mean. Natural soaps tend to lose color and scent over time. Although different recipes behave differently, we generally say that scent and color last 6-8 months. The soap itself is good for far longer. It’s all about oxidation. We use rosemary extract in our ready-to-ship blends as a natural preservative. We also offer Vitamin E oil in the Soapmaking Supplies on our website. Both are anti-oxidants and help stave off the loss of scent and color. Vitamin C can also be used, though we don’t use it ourselves very often. We’ve used it in custom soaps, but not enough to be certain of its effects. – Scott

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