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.


3 thoughts on “The Truth About Lye and Soap

  1. 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

  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..

Leave a Reply

Your email address will not be published. Required fields are marked *