Why does peroxide bubble
Peroxide bubbles when it is poured over blood because both blood and cells contain an enzyme known as catalase. Since the cut contains both blood and damaged cells, there is a lot of catalase available, which reacts with the peroxide to produce the foaming sensation. The foam forming is actually a chemical reaction which is taking place in the body. To better understand that chemical reaction, a bit more information on catalase is needed.
The main function of catalase is to catalyze the decomposition of hydrogen peroxide and break it down into just water and oxygen. Because catalase has one of the largest turnovers of all the enzymes in the human body, a single molecule of catalase has the ability to convert millions of molecules of both hydrogen peroxide and water per second, reducing them to just water and oxygen.
Catalase has the ability to react with hydrogen peroxide because of its basic make-up. It is composed of four polypeptide chains of amino acids, which are then strung together to create four porphyrin groups. pH plays an important factor in how catalase reacts with hydrogen peroxide in the body as well. Human catalase functions properly at 7, with a fairly broad range in which the reaction will not change, ranging from 6.8, all the way up to 7.5. For other catalases, the best pH can be anywhere from 4 to 11, depending on the species of creature.
Aside from the “bubbly reaction”, catalase is also responsible for removing hydrogen peroxide from milk and cheese before they go into production. In addition, catalase can be used in food wrappers, which will prevent the food from oxidizing. Another major application of catalase is the catalase test. This test is used by microbiologists to determine different species of bacteria, depending on the presence of the catalase enzyme in the bacteria. If applied to the bacteria, the same effect as on the scrapes can be observed, and this chemical reaction helps scientists identify many different species of bacteria.
Another more recent study has shown that low levels of catalase in the human body can play a significant role in the greying process of hair. Because hydrogen peroxide is a natural product of the body and catalase breaks it down, if there is a change in the catalase levels of the body, hydrogen peroxide cannot be broken down. This causes the hydrogen peroxide to bleach the hair from the inside out. Armed with this knowledge, many scientists are actively seeking ways to regulate the levels of catalase within the human body, so that a solution for grey hair could potentially be discovered.
All in all, because catalase is necessary for the deterioration of hydrogen peroxide, the bubbly effect won’t happen when you pour peroxide over your scrapes if there is nothing for it to oxidize, or there is no catalase present.