Sodium hydroxide safety: a guide for soap makers
Caustic soda (lye) is essential for soap making but highly corrosive. Here is how to handle, store, and mix it safely.
Sodium hydroxide (NaOH), also called caustic soda or lye, is essential for cold-process soap - but it is highly corrosive and reacts strongly with water. Treat it with respect.
PPE - non-negotiable
- Chemical-splash goggles (not just glasses).
- Chemical-resistant gloves.
- Long sleeves, closed shoes, and an apron.
- Good ventilation - the lye-water reaction releases fumes; avoid breathing them.
Mixing lye solution safely
- Always add lye to water - never water to lye (adding water to lye can erupt).
- Use a heat-safe container (the reaction gets hot, ~90 °C).
- Stir gently, keep your face away, and let it cool before use.
- Keep vinegar and running water nearby for spills on skin.
Storage
- Keep tightly sealed, dry, and clearly labelled - NaOH absorbs moisture and CO₂ from air.
- Store away from acids, aluminium, and out of reach of children.
First aid
On skin or eyes, rinse with plenty of water for 15+ minutes and seek medical help. Read the SDS in full before you start.
Buy caustic soda flakes and KOH for soap making, plus glycerine, fragrance, and colours - all with SDS and COA.
Frequently asked questions
Do you add lye to water or water to lye?
Always add lye to water, slowly. Adding water to lye can cause a violent, hot eruption. “Do as you oughta - add acid (or lye) to water.”
What PPE do I need for handling caustic soda?
Splash goggles, chemical-resistant gloves, long sleeves, closed shoes, and good ventilation. Keep water nearby for spills.