Generally, materials in this group are readily combustible. They behave as strong oxidants and therefore accelerate the combustion of other materials by providing molecular oxygen to the combustion site. Many peroxides are unstable and subject to explosive decomposition when shocked, heated, or rubbed. Explosions of peroxides have caused many fatal accidents.

Peroxides are good oxidizing agents. Organic compounds can ignite on contact with concentrated peroxides. Strongly reduced material such as sulfides, nitrides, and hydrides may react explosively with peroxides. There are few chemical classes that do not at least produce heat when mixed with peroxides. Many produce explosions or generate gases (toxic and nontoxic). Generally, dilute solutions of peroxides (<70%) are safe, but the presence of a catalyst (often a transition metal such as cobalt, iron, manganese, nickel, or vanadium) as an impurity may even then cause rapid decomposition, a build-up of heat, and even an explosion. Solutions of peroxides often become explosive when evaporated to dryness or near-dryness.

Often highly toxic and irritating to the skin, eyes, and mucous membranes.

The structure of the simplest peroxide H2O2 is H-O-O-H. Organic peroxides derive by the replacement of one or both of the H atoms in this compound by organic groups. Hydroperoxides result from the replacement of just one of the H atoms by an organic group. Thus, ethyl hydroperoxide has the formula C2H5-O-O-H. Some organic compounds form dangerous levels of explosive peroxides by autoxidation when exposed to the air during storage. These peroxides generally form slowly and are explosive when taken to dryness. Many peroxide solutions are inhibited to prevent decomposition to give oxygen and other products. Such reactions are often catalyzed by impurities in the absence of inhibition. When it occurs, such decompositions release very reactive free radicals that can initiate other reactions: peroxides are widely used as polymerization initiators. Peroxides are used in the paper industry (for bleaching), in making textiles (for bleaching), as oxidizers in organic synthesis reactions, as blowing agents, and in propellant formulations.

Benzoyl peroxide, peroxybenzoic acid, acetyl peroxide, cumene hydroperoxide, cyclohexanone peroxide, octanyl peroxide, diacetone alcohol peroxide.