The Foam in Hydrogen Peroxide

Remember to the last time you cut your hand and applied some hydrogen peroxide to the wound. You see it foam and bubble. Have you ever wondered what made it do that?

Typical bottle of hydrogen peroxide.

Before we explain how that happens, first you should know what hydrogen peroxide is. Hydrogen peroxide is an chemical name for a molecule that contains two atoms of hydrogen and two atoms of oxygen (H₂O₂). When you buy a bottle of hydrogen peroxide, it's actually 97% water and only 3 % hygrogen peroxide, but even if it was 100% hydrogen peroxide, the end result would still be the same.

Contained inside blood and skin cells is an enzyme called 'catalase'. This protein is very important to living things that are dependent on oxygen for reasons that are very complex to answer here, so take my word for it. Your blood and skin cells are full of this enzyme. When your skin is cut, then catalase is exposed to the air. If you pour hydrogen peroxide over the wound, it will bubble and foam because of a chemical reaction that's taking place. The catalase literally will convert the hydrogen peroxide into two compounds: water and oxygen. How? You'll have to go to a chemistry class to fully understand the details of this process, but the easiest way to explain is that it will take two molecules of H₂O₂ and change them into two molecules of H₂O and one molecule of O₂, which are water and oxygen molecules. This doesn't work when you just pour it on your skin because your skin isn't broken and no catalase is exposed to the hydrogen peroxide.

This is specifically happening because the catalase is in your cells, and if the cells are damaged, then the reaction can occur. But this isn't just humans that this reaction can take place in. Any living creature that has catalase in their system will have the same reaction to hydrogen peroxide. So, for example, an interesting experiment is to take a potato and slice it. If you pour hydrogen peroxide over this "wounded" potato, it will foam and bubble too. Another interesting note is that the reaction is very fast; one molecule of catalase can have reactions with as much as 5,000 hydrogen peroxide molecules, which is why it will bubble and foam so much.

Bet you didn't know that!