Why Does Hydrogen Peroxide Bubble on a Cut?

Why Hydrogen Peroxide Bubbles on Cuts
Catalase from blood and damaged cells speeds the breakdown of hydrogen peroxide into liquid water and oxygen gas bubbles.

Have you ever wondered why hydrogen peroxide bubbles on cuts and scrapes, yet doesn’t bubble on unbroken skin? Take a look at the chemistry that makes hydrogen peroxide bubble and learn what it means when bubbles don’t form.

Why Hydrogen Peroxide Forms Bubbles

Hydrogen peroxide (H2O2) forms bubbles when it decomposes into water (H2O) and oxygen (O2). The bubbles contain pure oxygen gas. Blood and cells in the human body contain an enzyme called catalase. Damage to tissue releases the catalase, which catalyzed the decomposition of hydrogen peroxide. Because it’s an enzyme, catalase isn’t used up by the reaction, so it continues to break down more peroxide molecules. Catalase supports up to 200,000 reactions per second.

Iron from the hemoglobin in blood also catalyzes peroxide decomposition. So, blood packs a double whammy when it comes to peroxide bubbling because it contains both iron and catalase from damaged blood cells.

What It Means When No Bubbles Form

Pouring hydrogen peroxide on unbroken skin does not produce bubbles because there isn’t enough catalase on skin to catalyze peroxide decomposition. Sometimes minor bubbling occurs because skin naturally hosts Staphylococcus bacteria, which produce catalase.

If you pour hydrogen peroxide on a wound and it doesn’t bubble, usually it’s because the peroxide is past its shelf life and has already broken down into water and oxygen.

Test Hydrogen Peroxide

Fortunately, it’s easy to text hydrogen peroxide for effectiveness. Simply splash a small amount into a sink and look for bubbles near the drain. Metals catalyze peroxide decomposition much like catalase. Another simple test is splashing peroxide onto a cut potato. Potato cells, like human cells, release catalase when damaged. If bubbles form, the peroxide is still good. If you don’t see bubbles, it’s time to replace the product.

Ensure hydrogen peroxide lasts as long as possible by storing it in a cool location in its original dark container or else away from light.

Pros and Cons of Peroxide as a Disinfectant

Because of its oxidizing properties, the first use of hydrogen peroxide was as a bleaching agent. Starting in the 1920s, peroxide became a popular rinse and disinfectant. Hydrogen peroxide disinfects wounds through three methods. First, because it’s a solution in water, it rinses away damaged cells and germs, while the bubbles help lift away debris. Second, the oxygen released by the decomposition of peroxide kills some types of bacteria and slows the growth and reproduction of the survivors. Third, peroxide acts as a sporicide, killing potentially infectious fungal and bacterial spores.

Despite its effectiveness, doctors and dermatologists don’t recommend using hydrogen peroxide to disinfect open wounds. The reason is because peroxide also kills fibroblasts, which are a type of connective tissue the body uses to repair injuries. Peroxide slows heal and increases the risk of scarring.

Some people use hydrogen peroxide as an aid to remove excess ear wax (cerumen). However, the reaction leaves warm water in the ears, which acts as a breeding ground for bacteria unless it is displaced with another chemical, such as alcohol. If a person has a ruptured eardrum, peroxide can worsen the situation.

The best uses of hydrogen peroxide as a disinfectant are for cleaning surfaces, disinfecting surgical instruments, and treating acne. Peroxide both disinfects and bleaches blood stains. Gargling or rinsing with hydrogen peroxide whitens teeth and helps reduce gum inflammation and plaque. However, it is important to use low peroxide concentrations (3% or less) and to spit it out rather than swallow it.


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