If you are using teeth whiteners you may be exchanging pearly whites for oral cancers. The active ingredient in most tooth whiteners used today is carbamide peroxide. In general, a carbamide peroxide gel is placed in a dental tray, which is then worn for anywhere from a few hours to overnight.
Although initially available from a dentist, these preparations have become available directly to consumers. Some of these products have concentrations of carbamide peroxide of up to 22 percent. Carbamide peroxide is composed of approximately 35 percent hydrogen peroxide, and when used as a whitener in an aqueous solution, it decomposes to release hydrogen peroxide and urea. The hydrogen peroxide is responsible for the tooth whitening effect of these products.
The discussion of the safety of tooth whiteners with peroxide has focused on the harmful effects of the free radicals generated in the whitening process. Although free radicals are produced by normal cellular metabolism, free radicals outside the cell can cause cellular damage by reacting directly with proteins, lipids, and nucleic acids. Past research showed that chronic ingestion of hydrogen peroxide increased the incidence of intestinal cancer in mice.
So the bottom line is be careful out there and use these products with caution. You might consider using blueberry or cherry capsules before and after by biting on the capsule and rubbing the liquid on your gums. The powerful antioxidants in the fruit capsules may limit the free radical production by the excess peroxide in the whitener. This is only my speculation but it seems a reasonable approach. Better safe than sorry.
Science Daily August 10, 2004