Degreasers can be solvent-based or contain some solvents, which is what produces the dissolving action on grease. Many use an extremely alkaline substance called sodium metasilicate, which becomes a powerful cleaning agent when combined with water. This substance is able to break down fatty acids easily, thereby removing grease and oil.
Some degreasers use sodium hydroxide combined with surfactants, which can be used to soak items to gradually dissolve grease and oil. Surfactants are commonly used in all kinds of detergents, as they reduce the surface tension of water in order to help penetrate and loosen dirt on dishes and catering appliances.