Substances that have the ability to oxidize other substances are said to be oxidizing and are known as oxidizing agents/chemicals. Oxidizers (e.g. hydrogen peroxide, potassium dichromate, sodium nitrate) are  not necessarily combustible in themselves, they are substances that cause or contribute to the combustion of other materials.

Organic peroxides are thermally unstable and may exude heat whilst undergoing exothermic autocatalytic decomposition. Additionally, organic peroxides may be liable to explosive decomposition, burn rapidly, be sensitive to impact or friction, react dangerously with other substances or cause damage to eyes.

Oxidizing chemicals should be stored in cool, dry place and kept away from flammable and combustible materials, such as wood, paper, styrofoam, plastic, flammable organic chemicals, and away from reducing agents, such as zinc, alkaline metals, and formic acid.

Oxidizers are indicated under GHS by flame-over-circle pictogram.