Sodium hydroxide (lye) is the one ingredient in cold process soap making that demands consistent respect and caution. When handled properly with the right gear and habits, lye is safe to use at home.
Essential safety gear: chemical-resistant goggles (not glasses), chemical-resistant gloves, long sleeves, long pants, and closed-toe shoes. Keep white vinegar nearby for neutralizing lye spills on surfaces — but never apply vinegar directly to skin that has contacted lye.
The golden rule of lye mixing: always add lye to water, never water to lye. Adding water to lye can cause a violent eruption. Pour lye slowly into the water while stirring gently. The solution heats rapidly and releases fumes — always mix in a well-ventilated area or under a range hood.
Use only stainless steel, heavy-duty plastic (HDPE #2 or #5), or heat-resistant glass containers for lye solution. Never use aluminum — lye reacts with aluminum and produces toxic, flammable hydrogen gas.
Store lye in its original container, tightly sealed, in a cool, dry place out of reach of children and pets. Always label lye solution clearly. Never leave lye solution unattended where someone might mistake it for water.
If lye touches your skin, rinse immediately with plenty of cool running water for at least 15 minutes. Remove contaminated clothing. Do not use vinegar on skin — it creates a heat reaction. Seek medical attention for serious burns.