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As we all learned in school, ordinary water is made up of two atoms of hydrogen and one of oxygen – hence the formula H2O. Hydrogen peroxide, as its name says, has an extra oxygen atom. Thus, hydrogen peroxide (its scientific name), or H2O2, is formed. “It is a very dangerous substance, which can cause serious damage to the skin if used pure. For this reason, it is only used in that state by professionals in chemical laboratories”, says pharmacist José Carlos Nassute, from the São Paulo State University (Unesp). The hydrogen peroxide sold as an antiseptic in pharmacies is diluted in ordinary water, with its concentration classified in volumes – the weakest is volume 10, for home application, while volume 20 is more used in hospitals. A detail to be observed is that, due to its additional oxygen atom, the substance becomes very unstable – meaning that, if exposed to air, this atom is easily released.
Not only does this require the vials to be kept tightly closed, but it causes the hydrogen peroxide to chemically react with the blood and plasma exposed in a wound, releasing the “left over” oxygen atom. It is this release that makes the liquid bubble – leaving, then, only ordinary water. “It is used for asepsis (cleaning) wounds because, in this process, it ends up killing 60% of the bacteria that could cause inflammation at the site,” says José.