Welcome to brain Stuff from how Stuff Works dot Com where smart happens. Him Marshall Brain with today's question, why does hydrogen peroxide foam when you put it on a cut? Hydrogen peroxide is something that you buy at the drug store. What you're buying is a three percent solution, meaning the bottle contains water and three percent hydrogen peroxide. It's not bad for washing cuts and scrapes, and the foaming looks cool. The reason why it foams is because blood and cells
contain an enzyme called catalase. Since a cut or scrape contains both blood and damaged cells, there's lots of catalase floating around. When the catalase comes in contact with hydrogen peroxide, it turns the peroxide into water and oxygen gas. The bubbles you see contain the oxygen. Catalase accelerates the decomposition of hydrogen peroxide and does this extremely efficiently, up to
two thousand reactions per second per molecule of catalase. The bubbles you see in the foam are pure oxygen bubbles being created by the catalase. Try putting a little 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 does not foam in the bottle or on your skin because there's no catalase to help the reaction to occur. Hydrogen
peroxide is stable at room temperature. Do you have any ideas or suggestions for this podcast? If so, please send me an email at podcast at how stuff works dot com. For more on this and thousands of other topics, go to how stuff works dot com.