What Is Lye & Why Is It Used For Soap Making

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If you’ve spent time here at SavvyHomemade, you’re probably wondering about the use of lye in soapmaking.

Some of you may have heard of lye (or caustic soda) before. Whether it was in high school science class or maybe at the hardware store. If so, I’m sure you know that it’s absolutely amazing at cleaning out clogged up drains.

But, misconceptions and misinformation about its safety are rife on the internet, particularly when it comes to its role within soap making. So, I thought I’d take a few hours out of my day to write everything you need to know about lye in one concise post. Well, I’ve tried to make it as concise as possible.

lye for soap making

What Exactly Is Lye?

So what exactly is lye? It’s a general term for two different alkaline compounds known as Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH). They are highly water-soluble and are sometimes referred to as caustic soda. 

In high school science class, you probably discussed the PH scale with its three levels, alkali, neutral and acid. On this scale, it’s likely you noticed 3 different compounds.

Usually, they use hydrochloric acid, water, and sodium hydroxide for this. It’s how chemistry students learn the difference between acids and alkalis. Without turning this post into a convoluted mess of unnecessary chemistry, all you really need to know is that lye is an alkali and not an acid. 

What Is Lye Made Of?

Traditionally, lye was made from wood ash with a process called ‘leaching’. This is where substances are extracted with solvents. Nowadays, it is produced using a complicated process. It’s best I don’t attempt to explain… Because I’m definitely not a chemist. If you’re interested, the web is full of interesting information about this. 

Personally, I wouldn’t worry about making lye from scratch, there would be too many things that could go wrong & it’s not that expensive. I have managed to buy lye for soap making many times at a reasonable price. This is similar to making your own essential oils, it can be done but… Why bother!

Measure out your lye crystals and water in separate containers

What Is Lye Used For?

Lye has a history spanning thousands of years and has been essential in creating many products including soap, food, and paper. Additionally, it has played a crucial role in the production of other items, such as drain cleaner, oven cleaner, glass cleaner, and fertilizer.

But did you know that it’s also used to make or process certain types of breads, olives, pretzels, noodles, and many more things? Strange, right? Not in reality. It’s a versatile compound! 

When it comes to soap-making, lye is an indispensable component. Although all genuine soaps incorporate lye, there are synthetic alternatives like phthalate-free glycerin that can be used. However, soaps made with these substitutes lack botanical elements and essential oils derived from plants and flowers, so can’t really be categorized as natural soap.

How Is Lye Used For Soap Making?

So how is Lye used to make soap? It’s what begins the chemical reaction that ends with lovely, bubbly, creamy bars of soap! 

If you’ve seen one of my soap recipes, you’ll notice I always have 3 things in my recipe. Some kind of oil (usually a combination of liquid or solid fats), water, and lye (caustic soda). 

A Little Science

When these 3 ingredients come together in the right combination and the right order, a chemical reaction called ‘saponification’ takes place. We sometimes shorten this to just ‘sap’. This converts much of the oily fat into what we know as soap, usually over a 24 hour time period. 

On a side note, if you haven’t seen it yet, check out my free soapmaking calculator and formulation guide. It helps you with the quantities and saponification values of your chosen oils and also gives you the water value.

If you enjoyed science class, you’ll know that some compounds are attracted to water (hydrophilic) and some compounds are attracted to oil (lipophilic). You’ll also know that these substances repel the opposite of what they are attracted to. Try pouring oil in water. You’ll notice the oil sits on top instead of dispersing. 

Hydrophilic and Lipophilic

With this in mind, think about two of the ingredients we’ve used in our soap recipes, oil and water. While these won’t traditionally mix together, the chemical reaction (sap) forces these compounds to ‘fuse’ at a molecular level. This creates a substance that is both hydrophilic and lipophilic (water and oil-loving). 

So when your hands are greasy and you go to use a bar of soap to clean it off, the lipophilic half of soap molecules immediately attach themselves to oily molecules that make up the grease on your hands. 

Then, as you wash away the soap, the hydrophilic half of your soap molecules attach themselves to the water that rushes over your hands. This begins a tug of war that ultimately results in the grease on your hands breaking apart and flowing down your drainpipe, molecule by molecule. 

hand washing

Sodium Hydroxide vs Potassium Hydroxide

Earlier on, when I defined what lye is, I talked about how it can be two different compounds. It’s either sodium hydroxide or it’s potassium hydroxide. But what’s the difference between the two? 

So, for our purposes (which is soap making), all we need to worry about is whether we’re making a solid bar of soap or making liquid soap

  • When sodium hydroxide is used, the chemical reaction (sap) produces a solid bar of soap. While sometimes they’re creamy and other times they’re more brittle depending on your recipe, they’re still essentially a solid.
  • On the other hand, when we use potassium hydroxide, we end up with a thick, slimy paste that can be diluted to make liquid soap.  

This is an oversimplification, but you get my drift.

In sum, sodium hydroxide gives us solid soap, potassium hydroxide gives us liquid soap, and that’s literally it! While there are probably many other differences between the two, that’s all we really need to know as soap makers. 

lye for soap making

Can Soap Be Made Without Lye?

The short answer here is yes and no. So let’s extrapolate.

The word ‘soap’ is kind of thrown about nowadays and doesn’t really have the same meaning it once used to. So what actually is a soap? 

A ‘true soap’ is one that has been made using oil, water, and lye and has been allowed to saponify. However, the advent of surfactants during the last century kind of changed the game a little. Now, many of us use detergents to clean our skin on a daily basis, instead of making use of true soap. 

Good examples of these pretend soaps are shower gels, body washes, bubble baths, shampoos, and conditioners. They tend to be liquid soaps, as they’re easy to make. In fact, you can learn how to make them here on my blog using natural surfactants.

So now we understand this

Let’s split the question into two and rephrase slightly. Can you make a true soap without lye? Absolutely not. But can you make a safe, soap-like detergent that will clean skin without using lye? Absolutely you can. 

Also, when people say ‘lye free soap recipe’, and call for something like a melt and pour soap base, you need to keep in mind that lye was used to make your M&P base before you could buy it. It’s just that you don’t have to use it yourself to follow the recipe in question. The only way to actually make soap and avoid it altogether is to make it with surfactants. 

Is Lye Safe And Non-Toxic?

Okay, so this is a loaded question because lye certainly is not a ‘safe’ ingredient that can be used without caution. So let’s break it down and get to the facts.  

Let me start off by first saying yes, lye is non-toxic. Earlier on I talked about how it is used to make or process certain foods. In fact, you can actually get your hands on ‘food-grade’ lye for that very purpose. 

However, it is a very powerful alkali. A lot of people talk about how acids can cause horrible burns. This is true, but on the other end of the spectrum, alkali can do exactly the same thing and in a very similar way. 

Having said that, I must stress that working with lye simply requires a bit of common-sense. I certainly haven’t written this article to dissuade anyone from making soap, as I have found it a truly rewarding hobby.

Common-Sense Safety

Combine your caustic soda to your water, making sure it's in a heatproof jug.

With a little experience, you will soon see that once you get your soap through saponification the real danger is over with.

Through all the years that I’ve been making soap, I’ve never had a serious burn. I’ve had small accidents, getting lye water or soap batter on my skin some times, but I always manage to wash it off quickly. I’ve learned that it’s all about being prepared. As long as you react to it properly, you shouldn’t have issues.  

When working with lye, it’s important to make sure we’re handling it properly.

  • For your first time making soap. Please study my beginner’s soapmaking post in detail and watch the video. Follow the correct process, which is definitely not that difficult, and you should be fine.
  • Always use PPE (personal protective equipment). This should include safety goggles/glasses, plastic or rubber gloves, and always wear long sleeves and full-length pants. You may also want to use a good quality apron. 
  • Ensure ventilation. When you mix water and lye together, they begin to react together. Chemical reactions can result in many different end results, but nearly all of them give off some kind of gas. While the fumes associated with lye and water aren’t in any way toxic, they can actually cause chemical burns to your lungs. As a general rule, it’s never a good idea to breathe in anything other than clean, fresh air. So when working with lye, ensure you’re in a well-ventilated room. If you’re working in your kitchen, maybe keep your windows open. If you’re in a lab without windows, ensure the room has been fitted with proper ventilation before attempting to make soap.

Nevertheless, even if you take all the precautions you can, sometimes accidents happen. We’ll discuss that next. 

Accidents Happen, What To Do About It?

So you’re using PPE and doing everything you can to minimize accidents, but you still manage to run into trouble?

The most important advice I can give you, first and foremost, is not to panic. When we panic we make silly decisions. Instead, keep calm, and follow the advice below. Commit this, as much as possible, to memory. It’ll save you time. 

Contact With Skin or Eyes

If lye is spilled onto the skin, rinse immediately with cold running water for a minimum of 15 minutes. After, if your burn is painful, seek medical attention. 

If lye gets into the eyes, immediately remove any contacts you might be wearing and rinse with cold running water for a minimum of 15 minutes. When it comes into contact with the eyes, it can cause blindness, so it is always advised to seek medical attention even if you believe your eyes have not been severely burned. 

  • DO NOT attempt to neutralize the lye with vinegar. I never recommend this. This can expedite the chemical reaction and cause severe, exothermic burns. 
  • DO NOT attempt to seek medical attention before rinsing your skin or eyes with cold running water. Getting your skin or eyes clear of lye is your number 1 priority to minimize the chance of severe burns or blindness. If you have a spouse, partner, friend, or family member with you, they can call for help for you while you handle this. 

Contact By Mouth

If lye or fresh (uncured) soap is swallowed, it can cause severe burns to the esophagus and even death. If you do swallow a little by accident, drink plenty of clean, ordinary water. 

You must then call for the emergency services (911 in the US) and then poison control (1-800-222-1222 in the US) in that order.

DO NOT attempt to induce vomiting at any time. 

Contact With Larger Areas Of The Body

If you spill lye on a larger part of your body, immediately remove the affected articles of clothing and rinse the skin with cold running water for 15 minutes. After, if your burn is painful, seek medical attention. 


If you spill liquid lye, immediately clear the area of any children and pets. Then, pour water onto the spillage. Pour slowly and carefully to minimize splashing. This will begin to neutralize the lye and make it safer for you to clear up. Use rags to absorb the water/lye mixture. Then mop the area thoroughly with ordinary water and detergent as you normally would. It is advised to remove your clothes and wash them as soon as you’re done cleaning the spill. Maintain your soap making PPE throughout. 

If you spill solid lye flakes, beads, or crystals, immediately clear the area of any children and pets. Then sweep the area, being careful to collect everything, and avoid contact with your skin. You should then mop the area with ordinary water and detergent like you normally would. Maintain your soap making PPE throughout. 

After clean up, you may wish to spray the area with a vinegar solution. This should be fine and will neutralize any remaining caustic residue if there is any. Do not ever apply vinegar to your skin to neutralize lye in this way. 

DO NOT leave any spillages to clean up later. At best you may damage whatever comes into contact with the spillage, at worst you will endanger others (including pets) in the immediate area. Always clean up a chemical spillage immediately. 

Considerations For Those With Children And Pets. 

  • If you have young children or pets around when making soap, never leave your lye unattended. It is best to keep the area you are making soap completely off-limits to pets and children when you’re working. Better safe than sorry. 
  • Older children should be educated about the dangers of lye so that they know to avoid your workspace when you’re soapmaking. 

I know, this all sounds super scary! But providing you’re minimizing the risks and know exactly what to do when accidents happen, you should be totally fine. We all do things on a daily basis that are terribly dangerous. Driving a car, for instance. With experience, you’ll find using lye is not nearly as intimidating as it seems. 

Final Thoughts

So that’s all you really need to know about lye, including how to minimize risks and handle it safely. Like I just said, it can seem like an intimidating or complicated ingredient to work with, but really it’s not all that bad.

Nevertheless, if you don’t think you’re ready to handle lye just yet, but still want to make some lovely soaps, take a look at my melt and pour soap recipes. These don’t require any lye at all to make yourself at home. Keep in mind that lye was used to make your M&P soap base.

Author: Angela Wills

Title: Founder and Author - Savvy Homemade

Expertise: Beauty Recipes, Skincare Formulation, Soapmaking, DIY Crafts, Parenting

Angela Wills is an author, founder, and the driving force behind Savvy Homemade. With over fifteen years of experience, she brings a wealth of knowledge and dedication to every post she writes. She is fearlessly dedicated to creating tried and tested beauty recipes, skincare formulations, soap recipes, and many other DIY crafts that will work for everyone. Angela has a Diploma in Skincare Formulation, is a proud member of the Handcrafted Soap & Cosmetic Guild, and infuses each DIY product with her passion and expertise.

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