Lye is a corrosive alkaline substance, commonly, sodium hydroxide (NaOH). Previously, lye was among the many different alkalis leached from hardwood ashes. In modern day, lye is commercially manufactured using a membrane cell method, which is an improvement from the previous diaphragm cell methods of Castner-Kellner, Gibbs, and Nelson.
Solid dry lye is commonly available as flakes, pellets, microbeads, and coarse powder. It is also available as solution, often dissolved in water. Lye is valued for its use in food preparation, soap making, biodiesel production, and household uses, such as oven cleaner and drain opener.
Solvation of sodium hydroxide is highly exothermic, and the resulting heat may cause heat burns or ignite flammables.
Avoid all contact with organic tissue (including human skin, eyes, mouth, and animals or pets). Keep away from clothing. Avoid all contact with aluminium.
The combination of aluminium and sodium hydroxide results in a large production of hydrogen gas: 2Al(s) + 6NaOH(aq) → 3H2(g) + 2Na3AlO3(aq). Hydrogen gas is explosive; mixing lye (sodium hydroxide) and aluminium in a closed container is therefore dangerous. In addition to aluminium, lye (sodium hydroxide) may also react with magnesium, zinc (galvanized), tin, chromium, brass, and bronze to produce hydrogen gas and is therefore dangerous. Do not allow lye to contact these metals.
Lye may react with various sugars to generate carbon monoxide, which is a poisonous gas; mixing sodium hydroxide and sugar in a closed container is therefore dangerous. Do not allow lye to contact sugar.
Hygroscopic substances are often used as desiccants to draw moisture away from water-sensitive items. Desiccants should never be placed inside a canister of lye because lye has much stronger hygroscopic properties than activated carbon and silica gel (the most common ingredients in commercial desiccant packets) and will pull and absorb the water from the desiccant packets. Do not place desiccant packets inside containers of lye.
Lye should be stored in air-tight plastic containers. The containers should be labeled to indicate the potential danger of the contents and stored away from children, pets, heat, and moisture.