Hydrogen peroxide (H₂O₂) is a very pale blue liquid, slightly more viscous than water, that appears colorless in dilute solution. It is a weak acid, has strong oxidizing properties, and is a powerful bleaching agent. It is used as a disinfectant, antiseptic, oxidizer, and in rocketry as a propellant.^[2] The oxidizing capacity of hydrogen peroxide is so strong that it is considered a highly reactive oxygen species.

In organisms, hydrogen peroxide is naturally produced as a byproduct of oxygen metabolism; virtually all possess enzymes known as peroxidases, which harmlessly and catalytically decompose low concentrations of hydrogen peroxide to water and oxygen.