One of the main functions of peroxisomes is to detoxify the cell by splitting hydrogen peroxide. They contain the enzyme catalase. Catalase converts H2O2 (hydrogen peroxide, a toxic byproduct of cellular metabolism) to H2O and O2, with 4H2O2 → 4H2O + 2O2.
Peroxisomes also catalyze the first two steps in the synthesis of ether phospholipids, which are later used to build membranes. In humans, peroxisomes are also responsible for oxidation of long-chain fatty acids. Peroxisomes also contain other oxidative enzymes such as D-amino acid oxidase and urease oxidase.