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What Is Lye?

Lolo Parker

Lye is the common name for sodium hydroxide, also called caustic soda. It is an alkaline substance, meaning it has a pH greater than seven.

Historical Production

Traditionally, lye was produced by pouring water through wood ashes as part of the soap-making process.


Lye is a white, solid material that can be broken down into flakes, pellets or powder. It is hygroscopic, meaning it absorbs moisture from the air, and exothermic when dissolved in water, meaning it can produce heat.

Common Uses

Crafters still use lye for soap-making, and it also is found in chemical cleaning products such as drain cleaners. Food-grade lye is used to cure olives and lutefisk.


Use gloves, safety glasses and face masks when handling lye, and work with it in a well-ventilated area.


Lye is corrosive and can damage the eyes and skin. It is deadly if ingested in sufficient quantities. When lye is mixed with sugar, it produces carbon monoxide, a potentially fatal gas.