Hydrolysis is a chemical reaction during which one or more water molecules are split into hydrogen and hydroxide ions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by step-growth polymerization. Such polymer degradation is usually catalysed by either acid, e.g., concentrated sulfuric acid (H2SO4), or alkali, e.g., sodium hydroxide (NaOH) attack, often increasing with their strength or pH. Hydrolysis is distinct from hydration. In hydration, the hydrated molecule does not "lyse" (break into two new compounds). It should not be confused with hydrogenolysis, a reaction of hydrogen.