Pure hydrogen peroxide is composed of two molecules of hydrogen and two molecules of oxygen, so its chemical formula is H2O2. However, the hydrogen peroxide sold in most stores is actually a solution, which typically only contains around 3 percent hydrogen peroxide and 97 percent water. This is because any solution containing more than 8 percent H2O2 can burn the skin.
Hydrogen peroxide has a number of different uses, including as a bleaching agent for cotton and also wood pulp. It is also used to make rocket fuel and other chemicals, as well as in a number of medicinal and cosmetic products.
Many people use a mild hydrogen peroxide solution to wash and clean out cuts, scrapes and other minor injuries, and it is sold over the counter for this purpose. When cleaning a cut with hydrogen peroxide, the solution usually starts foaming. This is due to the enzyme catalase, which is found in blood and other cells. When catalase comes into contact with hydrogen peroxide, it causes a chemical reaction that splits the H2O2 into oxygen gas, or O2, and water, or H2O. The foaming itself is caused as the oxygen gas is released and bubbles up through the liquid water.