Hydrogen peroxide is a chemical compound with the formula H
2. In its pure form, it is a colourless liquid, slightly more viscous than water; however, for safety reasons it is normally used as an aqueous solution. Hydrogen peroxide is the simplest peroxide (a compound with an oxygen–oxygen single bond) and finds use as a strong oxidizer, bleaching agent and disinfectant. Concentrated hydrogen peroxide, or "high-test peroxide", is a reactive oxygen species and has been used as a propellant in rocketry.
Hydrogen peroxide is often described as being "water but with one more oxygen atom", a description that can give the incorrect impression of significant chemical similarity between the two compounds. While they have a similar melting point and appearance, pure hydrogen peroxide will explode if heated to boiling, will cause serious contact burns to the skin and can set materials alight on contact. For these reasons it is usually handled as a dilute solution (household grades are typically 3–6% in the U.S. and somewhat higher in Europe). Its chemistry is dominated by the nature of its unstable peroxide bond.