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

By: Yara Simón  | 
a bottle of hydrogen peroxide beside a closed first aid kit
Many people include hydrogen peroxide in their home first aid kits, but the chemical doesn't disinfect wounds like all its fizzy business might lead you to believe. Jupiterimages / Getty Images

Hydrogen peroxide (H2O2) is a common bleaching agent that you can buy at the drugstore. What you are buying is a 3 percent solution, meaning the bottle contains 97 percent water and 3 percent hydrogen peroxide. Most people use it as an antiseptic.

It turns out that hydrogen peroxide is not very good as an antiseptic, but it is not bad for washing cuts and scrapes, and the foaming looks cool. So why does hydrogen peroxide bubble? Let's dive into the science behind the foamy display.


What Is Hydrogen Peroxide?

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.


Explaining the Hydrogen Peroxide Fizz

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.


Why Doesn't Hydrogen Peroxide Bubble in the Bottle?

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.