Any well-equipped first-aid cabinet probably includes a bottle of the antiseptic hydrogen peroxide.

Pour a little of this clear liquid on a cut or scrape and an instant foam of tiny bubbles appears. Just watching the foam is enough to make you feel you've accomplished something, but where do the bubbles come from, and do they really help?

In fact, the cells of your body are well acquainted with hydrogen peroxide, which is a normal, but toxic by-product of a cell's everyday activities. To get rid of this by-product, animal cells contain an enzyme called "catalase" which turns hydrogen peroxide into harmless water and oxygen. When you pour hydrogen peroxide directly into a cut, the catalase works overtime, producing water along with millions of tiny oxygen bubbles. You won't see the bubbles if you pour hydrogen peroxide onto the surface of your skin because the catalase is inside the skin cells, but a cut or abrasion is filled with catalase from the damaged cells.

The question stil remainds though, do the bubbles accomplish anything? The main thing hydrogen peroxide does is kill bacteria, which it can do because bacterial cells don't contain any catalase. Without catalase, the bacteria has no protection against hydrogen peroxide and is quickly destroyed. The physical bubbles may help as well by stirring things up inside the cut and dislodging specks of dirt that could be harboring germs.