Gargling with hydrogen peroxide is safe. Hydrogen peroxide kills bacteria in a person's mouth that causes bad breath. Hydrogen peroxide is used like a mouthwash as part of a daily oral hygiene regimen.
Optimal effect is realized by using hydrogen peroxide twice a day. As a matter of preference, a person can use a 100 percent hydrogen peroxide solution or can water the product down. A combination solution should contain at least 50 percent hydrogen peroxide to be effective. The oxygen contained in the hydrogen peroxide is the component that actually kills bacteria in the mouth. The regular use of hydrogen to gargle also results in somewhat whiter teeth for some people.