Lye Safety Guide: How to Handle NaOH and KOH Safely

Why Lye Is Dangerous

Sodium hydroxide has a pH of around 14 — highly caustic. Direct contact with skin causes chemical burns that may not be immediately painful (the nerve damage happens fast). Lye crystals produce heat and caustic fumes when dissolved in water. The solution can splash, erupt if water is added to lye rather than lye to water, and generate enough heat to crack glass containers.

None of this means you should avoid it — millions of soap makers work with lye safely every week. It means you need to treat it with the same respect you'd give a power saw: proper gear, proper process, no shortcuts.

Personal Protective Equipment (PPE)

• Safety glasses or goggles — glasses alone aren't enough; lye solution can splash from below or the side. Full goggles are safer.
• Rubber or nitrile gloves — heavy duty. Thin latex gloves can fail. Long cuffed gloves are best.
• Long sleeves and closed-toed shoes — protect arms and feet from splashes
• Apron — optional but smart for lye mixing and soap pouring

Keep PPE on from the moment you handle dry lye until your soap batter is in the mold and your tools are rinsed.

Safe Lye Handling — The Rules

1. Always add lye to water — never water to lye. Adding water to dry lye causes a rapid exothermic reaction that can erupt, splatter, and release caustic steam. Always have your water measured first, then slowly pour lye into it.
2. Use heat-safe containers. Lye solution reaches 180–200°F / 82–93°C. Thin plastic containers can warp or crack. Use high-density polyethylene (HDPE), stainless steel, or heat-safe glass.
3. Work in a ventilated area. Dissolving lye releases fumes that irritate the nose, throat, and lungs. Do it near an open window, under a range hood, or outdoors.
4. Never use aluminum. Lye reacts violently with aluminum, producing hydrogen gas. No aluminum pots, spoons, or measuring cups.
5. Keep children and pets out of the area while working with lye.
6. Never leave lye solution unattended. Label it clearly and keep it out of reach.
7. Let lye solution cool before combining with oils. Target 90–110°F / 32–43°C. Combining hot lye with cold oils (or vice versa) can cause ricing or acceleration.

If Lye Contacts Your Skin or Eyes

Skin contact: Rinse immediately with large amounts of cool running water for at least 15–20 minutes. Do not use vinegar or other acids to "neutralize" — this creates an exothermic reaction. Plain water is correct. Seek medical attention if the affected area is large or shows signs of a burn.

Eye contact: Flush with cool running water for at least 20 minutes, holding eyelids open. Seek emergency medical care immediately.

Ingestion: Do not induce vomiting. Rinse mouth, drink water or milk, and call poison control or seek emergency care immediately.

Know your local poison control number before you start soap making.

Storage and Disposal

Dry lye: Store in a sealed, airtight container (original packaging is usually best), in a cool, dry place away from moisture. Lye absorbs moisture from air (it's hygroscopic), which degrades its purity and can cause clumping. Keep away from children and pets.

Lye solution: If you have leftover lye solution, let it cool completely, label it clearly ("CAUSTIC — LYE SOLUTION"), and store in a sealed HDPE container. Use it for your next batch. Dispose of very small amounts by diluting heavily with water and pouring down the drain — check local regulations for larger quantities.

Use our Lye Calculator to calculate exactly the amount of lye you need — making it easier to avoid leftovers.