Hydrogen peroxide is a clear liquid chemical that looks just like water but acts as a powerful disinfectant and bleaching agent. Its chemical formula is H₂O₂, which means each molecule contains two hydrogen atoms and two oxygen atoms (regular water is H₂O, with just one oxygen atom).

You've probably seen the brown bottles of hydrogen peroxide in medicine cabinets. When you pour it on a cut or scrape, it fizzes and bubbles because it's releasing oxygen as it reacts with the blood and tissue. That bubbling action helps rinse away dirt and germs. Doctors and nurses use it to clean some medical equipment and surfaces.

Hydrogen peroxide also bleaches things by breaking down colored molecules. Hair salons use strong concentrations to lighten hair color, turning dark hair blonde. Scientists use it in laboratories for experiments, and manufacturers use it to bleach paper and textiles to make them white.

The concentration matters enormously. The bottles at home usually contain about 3% hydrogen peroxide mixed with water, which is meant for external use only. Industrial versions can be 30% or stronger and are dangerous to touch. Rocket engineers even use extremely concentrated hydrogen peroxide as part of some rocket fuels because when it breaks down, it releases a lot of energy.

Hydrogen peroxide should never be swallowed or put in your eyes. Even the weak solution in your medicine cabinet should be handled carefully and used only as directed on the label. It should also never be mixed with other household cleaners.