Sodium hydroxide, commonly known as lye or caustic soda, is a chemical used in the production of soap. The soap-making process, known as saponification, involves the reaction of sodium hydroxide with fats or oils. This chemical reaction breaks down the triglycerides in fats into glycerin and fatty acid salts, resulting in the formation of soap. Lye is a strong alkaline substance, making it crucial in ensuring the soap is effective at cleansing by emulsifying oils and grease. Safety precautions are paramount when handling lye, as it is caustic and can cause chemical burns if not used properly.