The oxygen-to-oxygen bond in a peroxide is weak compared to most chemical bonds. Because of this, peroxides break apart easily, sometimes with a burst of energy. When they break down, peroxides often release oxygen gas or form reactive fragments called free radicals.
This makes peroxides strong oxidizing agents, meaning they are good at pulling electrons away from other substances. Peroxides can be organic, with carbon groups attached to the oxygen-oxygen bond, or inorganic, like metal peroxides. Industries use peroxides as bleaches, disinfectants, and starter chemicals for making plastics.
A small amount of peroxide can kick off a chain reaction that turns liquid monomers into solid polymer chains. Because peroxides break down when exposed to light, they are usually stored in dark or brown bottles to keep them stable longer. Not every oxygen-containing compound is a peroxide.
Water (H2O) has oxygen bonded to hydrogen, not to another oxygen atom, so it is not a peroxide at all. Some organic peroxides, like benzoyl peroxide, are common ingredients in acne treatments, where they kill skin bacteria by releasing reactive oxygen. Concentrated peroxides can also be dangerously explosive, so chemists store and transport them with extra care.
Even old bottles of certain ether solvents can slowly form dangerous peroxide buildup just from sitting on a shelf exposed to air.