When you dab hydrogen peroxide on a cut, that white, fizzling foam is actually a sign that that the solution is killing bacteria as well as healthy cells. Hydrogen peroxide (H2O2), a compound made up of two hydrogen atoms and two oxygen atoms, begins to breaks apart as soon as it contacts blood, creating that stinging sizzle. This is because blood and most living cells contain the enzyme catalase, which attacks hydrogen peroxide and converts it into water (H2O) and oxygen (O2).