by Michelle Cutright

Ever wonder why hydrogen peroxide bubbles when you put it on an abrasion? The answer is actually very simple. The hydrogen peroxide (H2O2) decomposes into water and oxygen. The bubbles you see are oxygen bubbles. Even though US Peroxide uses a much more concentrated solution of H2O2 (50%), hydrogen peroxide is something you can buy at your local drugstore. What you are buying is a 3% solution meaning it's composed of 3% hydrogen peroxide and 97% water. 

A more detailed explanation of why it foams on an abrasion is because blood contains iron (heme) and cells produce an enzyme called catalase. Catalase is found in nearly all cells and organs and acts as a catalyst in the decomposition of hydrogen peroxide. Since a cut contains both blood and of course damaged cells, there is quite a lot of catalase present. When the H2O2 comes into contact with the catalase, it turns the peroxide into water (H2O) and oxygen gas (O2). Catalase breaks down the hydrogen peroxide extremely efficiently - up to 200,000 reactions/second. To see this reaction firsthand, I wouldn't recommend stabbing yourself, but you could pour some H2O2 onto a cut piece of potato to achieve the same results. The damaged potato cells contain catalase and will react with the peroxide in the same way. 

It may appear that hydrogen peroxide is not bubbling in the bottle, but actually the same reaction occurs only much slower. Without a catalyst, like catalase, hydrogen peroxide decomposes at a rate of about 1% each year. So pay attention to that expiration date, it may be time to buy some more.

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