Speaker 1: Welcome to brain Stuff from how Stuff Works dot Com
Speaker 1: where smart happens. Him Marshall Brain with today's question, why
Speaker 1: does hydrogen peroxide foam when you put it on a cut?
Speaker 1: Hydrogen peroxide is something that you buy at the drug store.
Speaker 1: What you're buying is a three percent solution, meaning the
Speaker 1: bottle contains water and three percent hydrogen peroxide. It's not
Speaker 1: bad for washing cuts and scrapes, and the foaming looks cool.
Speaker 1: The reason why it foams is because blood and cells
Speaker 1: contain an enzyme called catalase. Since a cut or scrape
Speaker 1: contains both blood and damaged cells, there's lots of catalase
Speaker 1: floating around. When the catalase comes in contact with hydrogen peroxide,
Speaker 1: it turns the peroxide into water and oxygen gas. The
Speaker 1: bubbles you see contain the oxygen. Catalase accelerates the decomposition
Speaker 1: of hydrogen peroxide and does this extremely efficiently, up to
Speaker 1: two thousand reactions per second per molecule of catalase. The
Speaker 1: bubbles you see in the foam are pure oxygen bubbles
Speaker 1: being created by the catalase. Try putting a little hydrogen
Speaker 1: peroxide on a cut potato and it will do the
Speaker 1: same thing for the same reason. Catalase in the damaged
Speaker 1: potato cells reacts with the hydrogen peroxide. Hydrogen peroxide does
Speaker 1: not foam in the bottle or on your skin because
Speaker 1: there's no catalase to help the reaction to occur. Hydrogen
Speaker 1: peroxide is stable at room temperature. Do you have any
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