Aug. 7, 2004 -- Do tooth-whitening products lead to oral cancer? New research suggests that it's certainly possible and a question that's worth further investigation.

Georgetown University Hospital researchers say the active ingredient in these popular whiteners -- available at a dentist's office or in over-the-counter kits -- may be the reason why two patients with no other identifiable risk factors developed advanced tongue cancer while in their 20s.

These popular tooth whiteners, whose use has tripled since 2001, are one of several possible explanations why there's been an increase in oral cancers in young people. About 90% of these cancers occur in people after age 45, usually the result of long-term smoking and drinking.

"But when these patients don't have a significant history of this use, you start to wonder what else they are being exposed to," says Bruce Davidson, MD, FACS, chairman of otolaryngology-head and neck surgery at the Washington, D.C., hospital.

Free Radical Damage Suspected

His suspicion: The hydrogen peroxide in the gels dentists apply to whiten teeth and in over-the-counter self-application bleaching kits to whiten teeth. Products are often labeled to contain carbamide peroxide, one-third of which is composed of hydrogen peroxide. In addition, when used as a whitener, carbamide peroxide changes into hydrogen peroxide, say the researchers.

In animal studies, peroxide has been shown to promote the growth of cancerous tumors inside the cheeks of rodents and cause gastrointestinal cancers when ingested. No tests have been done on humans.

Specifically, the theory is that when hydrogen peroxide leaks from trays containing the whitening gel onto surrounding areas inside the mouth, it triggers the release of cancer-causing "free radical" cells.

"Further testing is obviously required before we can be certain of a link, but people should be aware there is a possible link," Davidson tells WebMD. "If I was in the market for teeth whitening, I'd think twice about it. I make my career in treating head and neck cancers, so I'm also not going to go out and chew tobacco and smoke cigarettes, either."

No Additional Risks Noted

Research he presented Saturday at the 6th International Conference on Head and Neck Cancer documents two patients who developed advanced tongue cancer decades earlier than usual, after repeated use of tooth-whitening products.

Both patients were occasional drinkers, having no more than three drinks a week. One was a light smoker, the other didn't smoke.

They are among 19 oral cancer patients of all ages studied by Davidson's team of head and neck cancer surgeons. A middle-aged man who also developed tongue cancer used tooth-whitening polish, but the other patients didn't use bleaching products.

Among six patients who developed oral cancer before age 40, two used tooth whiteners, and both had more advanced cancer than the others, despite not smoking or drinking any more heavily.

The Reaction?

Terry Day, MD, director of head and neck oncologic surgery at Hollings Cancer Center at the Medical University of South Carolina and a spokesman for the American Academy of Otolaryngology-Head and Neck Surgery, says the study deserves notice because it points to why there's a growing trend in young people developing oral cancers -- especially affecting the tongue -- without a long-term history of those damaging vices.

"About 10% to 15% of oral and head and neck cancers do not seem to be related to tobacco and/or alcohol," he tells WebMD. "Other considerations still under investigation include genetic factors, the human papillomavirus (which causes genital warts), and nutrition factors. This study is interesting in that it points to the possibility of another factor being involved.

"But due to the small size, it's a serious limitation to whether or not you can say there's a relationship to teeth-whitening agents and oral cancer."

Until now, there has been little research on the long-term effects of tooth whiteners, and Davidson's study is believed to be the first to examine the link between cancer and tooth whiteners. Since they are considered "cosmetic" products, tooth whiteners don't fall under FDA regulation. While dentists have used these gels for some time, commercially available products have only been available for several years, so their long-term effects haven't been studied.

American Dental Association spokesman David Sarrett, DMD, a professor of dentistry at Virginia Commonwealth University, says there is no evidence that when used as directed, tooth whiteners increase cancer risk or cause other problems. But he does acknowledge they are abused by some people.

"Some patients are what we call 'tooth-whitening junkies' who are not satisfied until their teeth are snow white, and that's not achievable," he tells WebMD. "Even when using an over-the-counter whitener, I also advise people to first consult with their dentist, and always follow the product directions."

Leakage a Problem

When whiteners are applied by a dentist, which costs $200 or more, custom-fitted trays are used to hold the gel, reducing risk of hydrogen peroxide leakage; with over-the-counter products, the trays are usually not form-fitting.

But even under ideal conditions, reports Davidson, studies show that often less than 50% of the whitener is still in the trays one hour after application, indicating a lot of leakage.

Sarrett does caution against buying tooth whitening products over the Internet -- for another reason.

"They may have the right ingredients, but because they don't balance ingredients properly, they may not have the right pH, as with gels used by dentists or from reputable companies," he says. "It could be too acidic, which we know can damage tooth enamel."

SOURCES: The 6th International Conference on Head and Neck Cancer, Washington, D.C., Aug. 7-11, 2004. Bruce J. Davidson, MD, FACS, chairman, division of otolaryngology, Georgetown University Hospital, Washington, D.C. Terry Day, MD, director, division of head & neck oncologic surgery, Hollings Cancer Center; associate professor, Medical University of South Carolina, Charleston. David Sarrett, DMD, professor of dentistry and associate vice president of health sciences, Virginia Commonwealth University, Richmond; member, American Dental Association Council on Scientific Affairs.