Hydrogen peroxide

Hydrogen peroxide is a chemical compound consisting of two atoms of hydrogen and two of oxygen (H2O2). As such, it is very reactive and almost always transfers an oxygen atom to anything it comes in contact with.
It is produced naturally by several biological processes, including some that exist in the human body. In order to break it down quickly, the body also produces catalase, an enzyme, that immediately breaks it down into water and oxygen to prevent tissue damage.
Commercially produced hydrogen peroxide is used as an antiseptic.
Hydrogen peroxide at Wikipedia