Lye - Caustic Soda / Sodium Hydroxide Sodium Hydroxide (NaOH) is also known as Lye, Caustic Soda. This product, when dissolved in water, generates a lot of heat. Use extreme caution when adding product to water. Always add product to water never add water to product. Always use cold water (adding product to hot water may cause it to boil and spatter). Keep product tightly sealed in its original container. Product is a strong desiccant and will absorb enough moisture from the air to dissolve itself and become liquid. Product reacts strongly with metals containing Aluminum and produces Hydrogen gas. CAUTION: CAUSES SEVERE BURNS. Avoid contact with skin, eyes, mucous membranes and clothing. First Aid: External: Flood with water. Internal: Drink Large quantities of water. Call emergency room or physician immediately. Eyes: Flush with water for 15 minutes