Hydrogen peroxide retains its effectiveness for up to three years in an unopened container and six months in an opened container. Expired hydrogen peroxide is not detrimental, but it does lose potency.
A simple test to see if hydrogen peroxide is still effective can be performed by pouring a small amount into a bathroom sink. If the solution bubbles on the sink's surface, it is usable. Solutions with less than 5 percent hydrogen peroxide are useful as a first aid antiseptic or a cleaning product. Higher concentrations of hydrogen peroxide solution are used for some hair dyes and industrial bleaching products.