Why Does Hydrogen Peroxide Bubble When You Put It on a Cut?

At its core, hydrogen peroxide is a simple chemical compound with a not-so-simple chemical formula: H₂O₂. This formula reveals that two hydrogen atoms (H) and two oxygen atoms (O) make up hydrogen peroxide.

It foams is because blood and cells contain an enzyme called catalase. Since a cut or scrape contains both blood and damaged cells, there is lots of catalase floating around.

When the catalase comes in contact with hydrogen peroxide, it turns the hydrogen peroxide (H₂O₂) into water (H₂O) and oxygen gas (O₂).

Catalase does this extremely efficiently — up to 200,000 reactions per second. Hydrogen peroxide forms bubbles, which is pure oxygen bubbles being created by the catalase.

Pour hydrogen peroxide on a cut potato, and it will do the same thing for the same reason: Catalase in the damaged potato cells reacts with the hydrogen peroxide.

Hydrogen peroxide bubbles do not happen in the bottle or on healthy cells because there is no catalase to help the reaction occur. Hydrogen peroxide is stable at room temperature.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.