It decomposes to water and oxygen with rapid heat release. Some contaminants may cause hydrogen peroxide to decompose with explosive force. Caps on peroxide bottles should have some mechanism for releasing gas pressure that results from the decomposition. As a consequence of the reactivity of hydrogen peroxide, it is good practice to buy it in small bottles and store them in the refrigerator. Do not pour excess solution back into the bottle.
Many substances serve as catalysts for the decomposition of hydrogen peroxide.
Solid manganese dioxide is such a catalyst. Stabilisers are added to the commercially available material to slow this reaction. Hydrogen peroxide is normally stabilised with tin chloride, tetrasodium pyrophosphate, acetanilide or other similar organics. The solution can decompose violently upon heating, which may result in dangerous pressures. Spontaneous combustion may occur on standing in contact with readily flammable materials.