Hydrogen peroxide, which is a weak acid, does expire. If the container remains sealed, it retains its full strength for about one year. However, once the container has been opened, hydrogen peroxide lasts for only 30 to 45 days.
As soon as hydrogen peroxide is exposed to air, a chemical reaction begins, and the liquid starts changing into plain water. Every molecule of hydrogen peroxide has two hydrogen atoms and two oxygen atoms.
Hydrogen peroxide has many uses, such as bleaching textiles and wood pulp, making rocket propellant, and preventing infections. The medicinal hydrogen peroxide poured on injuries has a strength of 3 percent; anything above 8 percent is corrosive to the skin.