Study Linking Whiteners, Cancer Has Cavities

Do tooth whiteners (search) lead to oral cancer (search)? That was the disturbing question presented by Georgetown University researchers this week at a medical conference in Washington, D.C.

The active ingredient in most tooth whiteners used today is hydrogen peroxide (search). The researchers suggested that the free radicals (search) (highly reactive molecules) generated by the whitening process may damage cells in the mouth.

Although under ideal conditions, the peroxide-containing gel used in tooth whiteners would only treat tooth enamel and not come into contact with soft tissue in the mouth (search ), studies have shown that less than 50 percent of the whitener is present in the trays one hour after application, researchers said. They suggest the amount of leakage may be even greater in over-the-counter whitening products in which the trays are not custom fit by a dentist.

Although hydrogen peroxide may be rapidly metabolized in the mouth by a number of enzymes (search) and anti-oxidants (search), research has not focused on potential localized effects of high peroxide concentrations for extended periods of time, claimed the researchers.

To back up their hypothesis, the researchers pointed to past research indicating that long-term ingestion of hydrogen peroxide by mice increased the risk of gastrointestinal cancer and that the substance has been implicated as a tumor promoter in hamster cheeks. (The researchers apparently don't know that the hamster cheek study was retracted by its authors 10 days after it was published because the data were "mistakenly" interpreted.)

The researchers presented two case studies. In the first, a 26-year-old man with tongue cancer had used tooth whitening trays on multiple occasions in the previous two years and had used toothpaste with whitener. He claimed to be a non-smoker and only a light drinker. Smoking and drinking alcohol are recognized risk factors for oral cancer. In the other case study, a 22-year-old woman with tongue cancer had used a commercially available tooth whitening product for one month, three years earlier. She claimed to be only a light smoker and light drinker.

The researchers also presented the "results" of a study of 19 patients with oral cancer, three of whom reported a history of tooth whitener use in the past. All three tooth whitener users had regional lymph node disease compared to only three of 16 patients without a history of tooth whitener use. Reportedly, there was no significant difference in alcohol use and smoking history between the tooth whitener users and non-users.

Is any of this a reason to opt for yellow teeth? Hardly.

In the first place, the researchers readily acknowledged in their write-up that their study population was too small and lacked comparisons with a group of individuals without cancer. They also noted that the study subjects may have inaccurately reported their use of tooth whitening products, as well as smoking and drinking histories. Although oral cancers are rare in young people, the researchers noted, the two case studies involving young people may simply be examples of those rare cases who, by coincidence, also used tooth whiteners.

In short, their report scarcely can be called a "study." It consist entirely of scattershot, anecdotal data from which no implications, let alone conclusions, concerning tooth whitening products and cancer can be drawn. Although the researchers did acknowledge the only reasonable assessment of their data — "These data do not necessarily suggest a causative relationship between the use of these products and the development of cancer" — they concluded with the always distressing junk-scientist call for "more research":

"However, free radicals generated in the whitening process have carcinogenic potential, and therefore the uses of these products in this patient population should be further studied."

The bottom-line, however, is that no data indicate that hydrogen peroxide in any way causes or promotes cancer in humans. The World Health Organization's International Agency for Research on Cancer (search ) said, "There is inadequate evidence in humans for the carcinogenicity of hydrogen peroxide."

Moreover, given the widespread and increasing use of tooth whitening products— but no notable increase in reports of oral cancers— one might think the Georgetown researchers are simply trying to get media attention, scare the public and force either the National Institutes of Health (search ) or the tooth whitening product industry to provide them with lucrative research grants. Were these researchers responsible scientists or truly concerned about the public's health, they would have conducted a properly designed study before announcing any results.

Had they done so, of course, they likely would not have had any results to announce.

Steven Milloy is the publisher of, an adjunct scholar at the Cato Institute and the author of " Junk Science Judo: Self-Defense Against Health Scares and Scams" (Cato Institute, 2001).

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