Harsh Cleanser is a term used to describe a type of cleaning agent that is highly effective but can be damaging to surfaces if not used properly. The most common harsh cleanser is LYE, which is a caustic alkali substance made from ashes and used in various industrial processes. LYE is often used as a drain cleaner or oven cleaner, and it can also be used to make soap. It is important to use protective gloves and goggles when handling LYE, as it can cause skin and eye irritation.