Food - It can be used to wash or chemically peel fruits and vegetables. Furthermore, it is often used to soften foods like olives or baked goods.;Cleaning - Not recommended for drain cleaning;Soap - Typically for cold-process soap making, lye is essential. It can also be used in hot-process soap making when mixed with the appropriate fat and oils. Caustic soda (lye) creates a chemical reaction known as saponificiation. This process is what breaks down the oils and turns them into soap.;Hair - In liquid form, it is mixed with other ingredients to create a hair straightening substance (often referred to as a relaxer).