Lye Safety in Soap Making: A Decade of Safe Practice

The first time I opened a container of lye, I'll be honest, I was nervous.

Every warning label, every story I'd heard about chemical burns, and every "DO NOT TOUCH" message was flashing through my mind. Today, lye is simply another trusted tool in my workshop: treated with respect, but no longer feared.

You cannot make true soap without lye. But you can handle it in a way that keeps you, your family, and your workspace safe. In this post, I'll share how I approach lye safety in soap making after years at the curing rack, and how you can stay calm and confident around sodium hydroxide whilst still enjoying the creative side of the craft.

What Is Lye, Really?

"Lye" is a general term for strong alkalis used in soap making, usually sodium hydroxide (NaOH) for solid bars and potassium hydroxide (KOH) for liquid soap and some shave soaps.

The UK Health Security Agency describes sodium hydroxide as a white, odourless solid that is highly corrosive, capable of causing serious burns to skin and eyes if mishandled. Their overview on sodium hydroxide properties and incident management emphasises appropriate precautions when storing and using this chemical.

In other words: lye demands respect. But once it meets your oils and saponification is complete, no lye remains in the finished bar, just soap, glycerin, and any superfat you've chosen to leave.

Why Lye Has a Scary Reputation (and Why It's Still Used)

Lye is caustic. When dissolved in water, it forms a very alkaline solution that can burn skin and eyes on contact, releases heat as it dissolves (the solution can get very hot very quickly), and produces fumes that can irritate the lungs if you lean directly over the container.

Resources like the School of Natural Skincare's guide to lye safety and common hazards spell this out clearly: sodium hydroxide solutions must be handled with care to avoid chemical burns and eye damage.

Soap Queen's Back to Basics lye safety guide uses a comparison I like: driving a car. Cars can be dangerous, but we accept them as part of everyday life because we follow a set of safety rules. Lye is very similar.

For me, good lye safety has three pillars: respect the chemical, create a safe environment, and build calm, consistent habits.

My Non-Negotiable Lye Safety Rules

Here's what I do every single time I mix lye, whether I'm making a tiny test batch or a full studio run.

1. Dress for the Job

Before I even open the lye container, I put on safety goggles or wraparound glasses, long sleeves, closed shoes, and gloves resistant to splashes.

The School of Natural Skincare's list of essential lye safety tips emphasises that lye solutions can cause burns on contact and serious eye damage, which is why eye protection is a must, not a "nice to have."

I also tie back long hair and make sure I'm not wearing anything that drapes or could catch.

2. Prepare the Space

I never mix lye when children are around, pets can wander underfoot, or I'm distracted or rushing.

Instead, I choose a time where I can be fully present. I clear the workspace, lay out all equipment, and open a window or use an extractor fan. I keep white vinegar nearby, not because it magically neutralises spills (you'd need a lot for that), but because it's helpful for light residue and for peace of mind with small splashes on surfaces.

Professional resources like the Handcrafted Soap & Cosmetic Guild's overview of safe handling of lye for soap makers stress the importance of appropriate ventilation and prevention of exposure to children and pets.

3. Add Lye to Water, Never Water to Lye

The golden rule: Always add lye to water, never water to lye.

When sodium hydroxide dissolves, it gives off heat in an exothermic reaction. The solution can get hot enough to crack glass or warp cheap plastic. If you pour water onto a pile of dry lye, the top can seal and trap heat, leading to a volcano effect and dangerous splashing.

By slowly sprinkling lye into a larger volume of cool water, you control where the heat is generated, minimise the risk of splashes, and maintain better visibility of the solution.

The explanation of lye dangers in the School of Natural Skincare's safety article highlights exothermic heat and splashes as key risks to manage.

4. Stand Back from the Fumes

When lye first hits water, it releases fumes that can irritate your nose and throat. They dissipate fairly quickly, but for those first few seconds I stir gently with a long-handled utensil, turn my head slightly away, or step back for a moment, and avoid leaning directly over the container.

If you're especially sensitive, you can wear a simple mask while you mix. With time, you'll learn how quickly fumes clear in your particular space.

What To Do If Something Goes Wrong

Even with good habits, spills and splashes can happen. The key is not to panic, just act promptly.

Skin Splashes

If lye solution splashes onto your skin: Rinse immediately under cool running water for several minutes. Do not try to neutralise with vinegar on your skin; it can cause more irritation. If irritation persists, follow medical advice or seek help.

Eye Exposure

If lye gets into your eyes: Rinse with plenty of lukewarm or cool water for at least 15 minutes. Remove contact lenses if it's safe to do so. Seek urgent medical attention.

Worktop Spills

For small spills on the counter, wipe up carefully whilst wearing gloves, rinse the area thoroughly with plenty of water, and for peace of mind, a final wipe with a diluted vinegar solution can help deal with light alkaline residue on non-porous surfaces.

For larger spills, especially if there's a risk to others, follow local guidance for chemical spills and ventilate the area. The UK sodium hydroxide guidance gives a framework for incident management and environmental precautions.

Is Lye Itself "Safe" in Soap?

A common worry is: "How can something that can burn my skin be safe in a bar I wash with?"

The answer lies in the chemistry of saponification.

When formulated correctly, every molecule of lye reacts with fats to form soap. No free sodium hydroxide remains in the finished, cured bar, as long as the recipe uses a small superfat or lye discount for safety, measurements are accurate, and the bar is allowed to cure fully for several weeks.

Educational resources like The Healthy Porcupine's primer on what lye is and why it's used in soap make this clear: lye is a tool used during manufacturing, not an ingredient left in the final product.

How Lye Safety Relates to Skin Health

From a dermatology perspective, what matters in daily use is not the lye itself (which is gone), but the final bar: its pH (usually around 9 to 10 for traditional soap), its oil blend and superfat level, and whether it has been fully cured.

Studies on cleansers and the skin barrier show that harsh, alkaline products can disrupt the acid mantle and increase dryness, but that gentle formulations and appropriate moisturising can help maintain barrier function.

NHS and hospital guidance on emollients often advises people with dry or eczema-prone skin to avoid standard soaps and instead use emollient cleansers, as ordinary soaps can worsen dryness.

For The Humble Shepherd, lye safety is therefore paired with thoughtful superfat levels (see our post on understanding superfat and why 5% matters), gentle oil blends that respect the skin barrier, and a full 4 to 6 week cure, as described in why cold process soap takes 4 to 6 weeks.

FAQs: Lye Safety for Curious Customers

1. Is there lye in the finished bar of soap?

No. When a recipe is correctly formulated and fully cured, there should be no free lye left in the bar. The sodium hydroxide has reacted completely with the oils to form soap and glycerin. Superfat ensures a small amount of oil remains, not lye.

2. Is lye-free soap better?

"Lye-free" bars are usually either syndet bars (made from synthetic detergents) or melt-and-pour bases where the lye work was done earlier in a factory. They can be excellent products, but they are chemically different. True soap simply cannot exist without lye at some point in its creation.

3. Why can't I just use a "natural" alternative to lye?

Traditional wood ash lye is still lye. It's just less refined and harder to control accurately. Modern, pure sodium hydroxide allows us to calculate recipes safely and precisely. It's not less natural; it's simply more predictable.

4. Is it safe to make soap at home with children around?

You can make soap in a family home, but not with small children in the workspace when you're handling lye. The safest approach is: mix lye when children are out or asleep, keep lye and solutions stored securely and out of reach, and never leave mixed lye unattended.

Once the soap has saponified and cured, sharing the finished bars can be a lovely family ritual.

How We Build Safety into Every Bar at The Humble Shepherd

In my workshop, lye is never an afterthought. It's measured, handled, mixed, and cleaned up with the same quiet seriousness every time.

That allows me to focus my creativity on the parts you can see and smell: the way a bar feels in your hands, the gentle scent as you build a lather, and the calm it brings to your morning or evening routine.

If you'd like to bring carefully made, safety-conscious bars into your bathroom, you can explore our current soap collection and read more about our cold process method.

And if you'd love first access to fully cured, fresh-from-the-rack batches, you can join our Shop Now waitlist so we can let you know as soon as new bars are ready.