Catalase is an enzyme that assists to break down hydrogen peroxide to oxygen and water in the body. It is created by most of the body's cells. Hydrogen peroxide is created naturally by several processes that make up the metabolism so catalase prevents peroxide from building up in the body's tissues and causing damage. Like most enzymes, it remains unchanged by the transition, but it is particularly noteworthy that one molecule of catalase can break down about five million peroxide molecules. It is so effective that a catalase-positive bacteria can be tested for by treating a suspect sample with peroxide and looking for oxygen bubbles with the naked eye.