For centuries, people have been swishing and spitting hydrogen peroxide. Though prolonged exposure or high concentrations can cause irritation to the gums, tongue and roof of the mouth, and swallowing can damage the esophagus and internal membranes, using hydrogen peroxide for oral care is actually pretty common [source: OSHA]. Store-bought bottles are usually a 3-percent solution and are safe for oral use. The bottles are brown because H2O2 can weaken or become chemically unstable and ineffective if exposed to sunlight. At 97 percent water, the 3-percent solution will just turn to water over time.
Toothpaste with hydrogen peroxide also is effective. Some people make their own pastes with baking soda and H2O2 combined to increase the whitening and abrasive effect, but these mixtures should be used sparingly and in combination and at intervals as recommended by a dental professional. Too much abrasion can wear enamel and lead to gum irritation, so it's not a good idea to brush with this mixture more than once or twice a week. Store-bought peroxide toothpastes are available with and without baking soda and most are gentle enough for regular use, though some with sensitive teeth or pre-existing gum problems should check with a dentist or hygienist.
As far as adverse reactions to using hydrogen peroxide on teeth, temperature sensitivity and mild gum irritation are the most common issues, and they don't affect everyone [source: ADHA]. Checking with a dental office about how long and often you can use peroxide for specific oral problems or intensive whitening is advisable. Routine cleansing and rinsing are most likely safe, though running it by your dentist is never a bad idea.
So far so good for just over a buck's worth of product. Can hydrogen peroxide do anything else for your mouth? We'll investigate, next.