Every bar of real soap starts with lye. For bar soap that's sodium hydroxide (NaOH). For liquid soap it's potassium hydroxide (KOH). Lye is safe to work with when you respect it, and it can cause serious burns when you don't. These are the habits we follow every time.

Before you start

• Wear the gear: splash goggles (not just glasses), chemical-resistant gloves, long sleeves and long pants. Keep them on until cleanup is done, because fresh soap batter can still irritate skin.

• Clear the room: no kids, pets or distractions. Keep trip hazards out of the way.

• Ventilate: mixing lye with water gives off fumes. Open windows or run a fan, or mix outside. Don't lean over the container.

• Use the right container: sturdy heat-resistant plastic or heavy glass, with plenty of room. Never use aluminum, tin or zinc. Lye reacts with them and can release hydrogen gas.

• Weigh everything on a digital scale. Measuring cups aren't accurate enough for lye.

Mixing lye solution

1. Weigh the water (or other liquid) and the lye into separate containers.

2. Always add the lye to the water, slowly. Never pour water onto lye. Adding water to lye can make it erupt out of the container.

3. Stir gently until it dissolves. The solution can get as hot as about 200°F, so set it somewhere safe to cool.

4. Label it "LYE – DO NOT TOUCH" while it cools, and keep it where nobody can grab or drink it.

If lye gets on you

• Skin: take off any contaminated clothing and rinse with plenty of running water for at least 15 minutes. Get medical help.

• Eyes: rinse right away with running water for at least 15 minutes, holding the eyelids open, and get emergency medical help.

• Swallowed: get medical help immediately. In the U.S., call Poison Control at 1-800-222-1222 or 911.

• Don't use vinegar on skin. It doesn't stop a lye burn, and the reaction makes more heat. Water is what the safety data sheets call for. Vinegar is fine for wiping lye dust off counters during cleanup.

Storage

Keep lye in its original, tightly closed, clearly labeled container. Store it somewhere cool and dry, out of reach of children and pets. Lye pulls moisture from the air, so close the lid right after you measure.

Cleanup

Keep your gloves on. Wipe soap batter out of pots with paper towels, then wash with hot water and dish soap.

Sources - CDC/NIOSH Pocket Guide to Chemical Hazards: Sodium hydroxide (first aid: irrigate eyes immediately, flush skin with water; incompatible with aluminum, tin, zinc). https://www.cdc.gov/niosh/npg/npgd0565.html - Soap Queen (Bramble Berry): Back to Basics: Lye Safety Guide (gear, ventilation, lye-to-water, containers, 15-minute rinse, vinegar). https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/back-to-basics-lye-safety-guide/ - Soap Queen: How to Handle Potassium Hydroxide. https://soapqueen.com/bath-and-body-tutorials/tips-and-tricks/potassium-hydroxide-safety/ - Poison Control (U.S.): https://www.poison.org/