Hydrogen peroxide does eventually go bad especially after it's been opened.
After opening the hydrogen peroxide bottle the hydrogen peroxide loses it's effectiveness as a disinfectant after about a year.
An unopened bottle of hydrogen peroxide lasts for about 3 years before it goes bad.
Expired hydrogen peroxide is not harmful to use and can still help with a cut or sore but it's not as effective once it's expired.
You could still use the expired hydrogen peroxide to gargle with to keep your teeth and mouth clean as well and it is okay to put the hydrogen peroxide that is expired on sores.
But if you want the best results from hydrogen peroxide you should get a fresh bottle of it.
A fresh bottle of hydrogen peroxide is pretty cheap.
Hydrogen Peroxide loses it's effectiveness as a disinfectant once it's past its expiration date but it's still safe to use.