If My High School Chemistry Teacher Could See Me Now: Why Real Soap Requires Lye

I could never pretend to be a chemistry expert. In fact, if we went back in time to 1994 or 1995 when I took high school chemistry, there would be a few clues confirming that chemistry just wasn’t my thing. I technically passed the class, but even that was with a little help from my friends—if you know what I mean.

Fast forward to 2024 when I was introduced to tallow and then started researching soap making (because clearly that’s a natural progression), and my head was spinning—to put it lightly. So much science and chemistry! It made me wish I had paid a little more attention.

One of the most common questions I asked when I first heard about traditional soap making is: “Is lye soap safe?” The answer starts with understanding how real soap is actually made.

I read about cold process soap making, hot process soap making, melt-and-pour soap making, and rebatching. Literally all of these terms were foreign to me, so I kept reading. I ruled out melt-and-pour and rebatching right away because I wanted to have as much control over the process and the ingredients as possible.

At the time I had another autoimmune issue rear its ugly head, and I needed to eliminate as many chemicals, additives, and preservatives as possible.

The words lye, sodium hydroxide, and potassium hydroxide kept coming up, and my eyes would just glass over—not only because those words sounded way too chemistry-ish, but also because in my mind I needed absolutely no chemicals.

As I soon found out after much reading, true soap must contain lye. Then I learned a new word—saponification.

To me, that sounded like a completely made-up word. I honestly thought it was some kind of new-age internet trend, so anytime I came across it, I skipped to the next article. I’m not sure if that’s a Gen-X trait (being untrusting) or just my own stubbornness. Either way, the word sounded fake to me!

After reading countless blogs, articles, and historical descriptions of lye and saponification, I finally realized this was very much a real thing—and that I needed to start understanding it if I was going to make soap for me and my family.

Where Lye Comes From

Historically, lye came from hardwood ashes and water. Later, soap makers learned ways to refine those ashes into stronger forms of lye using lime. Today, most lye is produced through electrolysis of salt water in what’s called the chlor-alkali process.

It absolutely amazes me how our ancestors were so resourceful and figured things out out of necessity. I feel so inferior in many ways to what my ancestors must have been like. Today, I figure things out with the tiny computer in my pocket—wow, aren’t I brave and resourceful! (LOL)

This is one reason I’ve become so interested in old-fashioned ways of doing things. Things were simpler. Not easier—but simpler.

Lye actually has very old roots. Long before modern chemistry labs existed, people made it right at home. Early homesteaders discovered that when rainwater passed through hardwood ashes, it created a natural alkaline liquid. This liquid was used for making soap, cleaning, and even preserving food. That early form of lye was often called potash.

Today, most soap makers use a purified form of lye produced from salt and water through electrolysis. This creates a consistent, reliable ingredient that allows soap makers to craft high-quality bars every time.

The progression of lye throughout history

Method	Type of Lye	Era
Wood ash leaching	Potassium carbonate (weak lye)	Ancient–1800s
Potash refined with lime	Stronger potassium-based lye	1700s–early 1900s
Saltwater electrolysis	Sodium hydroxide	Modern

It really is amazing how God created these processes and how people discovered ways to use them.

So… Is Lye Safe?

As I kept reading, I kept asking the same questions:

Is this safe? Is this natural? Is there a better way to make soap?

I also learned that raw lye is very caustic and that when using it you must protect your skin, eyes, and lungs.

Well… that didn’t sound very healthy or natural.

That’s where chemistry—and the word saponification—finally started to make sense.

Lye is a strong alkaline substance that reacts with oils or fats in a process called saponification. During this reaction, the oils and lye transform into soap and glycerin.

Once the reaction is complete and the soap has cured, no active lye remains in the finished bar.

Most of the chemical reaction happens in the first day or two, but soap is typically cured for 4–6 weeks. This curing time allows excess water to evaporate and the bar to become harder and milder.

Soap makers even have a funny little test called the “zap test.” A tiny bit of fresh soap is lightly touched to the tip of the tongue. If it gives a quick electric “zap,” similar to touching a battery, the soap needs more time to finish reacting.

Don’t worry—I’m definitely not licking your soap before sending it to you!

During saponification, the lye and oils or fat (tallow in my case) combine and change into something entirely new. What you’re left with is:

• Gentle cleansing soap

• Naturally occurring glycerin

• A nourishing bar that’s safe for skin

Without lye, you wouldn’t have true soap—you would only have detergents.

Soap vs. Detergents

Soap is made when fats or oils react with lye through saponification.

Detergents, on the other hand, are usually synthetic cleansers made from laboratory-engineered surfactants rather than natural oils that have gone through saponification.

Both clean—but they are chemically different products.

The 3 Biggest Myths About Lye in Soap

Myth #1: Soap still contains lye

Properly made soap does not contain active lye. The lye is consumed during the saponification process and transformed into soap and glycerin.

Myth #2: Lye soap is dangerous for skin

Raw lye is dangerous, but finished soap is completely different. Once the chemical reaction is complete, the finished bar is safe to use.

Myth #3: “Lye-free soap” is better

All true soap must begin with lye. Products labeled “lye-free soap” are usually detergent bars, not traditional soap.

Confessions of a Modern Homesteader

After all of this research, I realized that if I wanted to make my own soap, I needed to overcome the scary lye word. So I did.

I might not be considered a “true” homesteader because I source my lye from Walmart and Amazon instead of making it in my backyard with rainwater and ashes. But as I said before—I do enjoy my modern conveniences.

I’m an internet-using, electricity-loving homesteader living on a small piece of land, trying to make healthy choices for my family and be as independent as possible while still taking advantage of the conveniences my ancestors didn’t have.

I do my absolute best to source ingredients for my soaps and lotions in the USA while also paying attention to products that are friendly to our planet.

You might call me a strange combination of a modern-hippy-conservative (if you wanted to put a label on me). In the 90’s though, I would have been called a tree-hugging-conservative!

I also have to weigh my time. We have two teenage kids in sports, and we homeschool. I just don’t have the time Caroline Ingalls had to make lye, render fat from her own cows, cook dinners from scratch, raise children, and chop firewood.

Well… I think Charles chopped the firewood, but you get my point.

Here’s another confession of a modern homesteader: even though we raise cows, we only have a few because our land is small. So, I buy grass-fed tallow from an American distributor. It’s high quality, it’s from the USA, and it allows me to support another small business while running my own.

If my high school chemistry teacher could see me now, he would probably be shocked that the girl who barely survived chemistry class is now willingly talking about things like lye and saponification.

While I may never become a chemistry expert, I’ve come to appreciate the simple science behind traditional soapmaking. What once sounded intimidating and unnatural turned out to be the exact process people have relied on for centuries to make real soap.

Sometimes the things that seem the most complicated are actually part of the most time-tested traditions.

And if you’re curious what traditional soap feels like, you can explore my handmade tallow soaps made with only good ingredients. Because apparently… somewhere along the way… chemistry and I became friends after all.

Frequently Asked Questions About Lye and Soap

Does handmade soap contain lye?

No. Lye is used during the soapmaking process but is consumed during saponification. Properly cured soap contains no active lye.

Why is lye needed to make soap?

Lye is what allows oils or fats to chemically transform into soap. Without lye, oils would remain oils.

Is lye soap safe for skin?

Yes. Once soap has fully gone through saponification and curing, it is safe for skin.

What is the difference between soap and detergent?

Soap is made from fats or oils and lye. Detergents are synthetic cleansers made from engineered surfactants.