It’s a ritual observed by thousands of Canadians every day: brush, floss, gargle and spit. Rinsing with mouthwash doesn’t just provide a scrubbed, minty feeling; it’s good for our health, we’re told, curbing plaque and gingivitis (not to mention bad breath). Some brands even carry the Canadian Dental Association’s official seal. But this so-called healthy habit could be doing more harm than good. Australian researchers recently concluded that mouthwashes containing alcohol may contribute to oral cancer.
Tobacco use is the biggest risk factor for oral cancer, according to the Canadian Cancer Society. Combined with excessive drinking, it’s even more dangerous—a heavy smoker and drinker is up to 30 times more likely to develop it. Even so, “there’s a small group of patients who don’t seem to have any risk factors,” says Michael John McCullough, an associate professor at the Melbourne Dental School and one of the experts behind the report. “I noticed some were saying they’d used alcohol-containing mouthwashes over a long period of time.”
In the article, published in the Australian Dental Journal in December, McCullough and co-author Camile Farah conclude there is now “sufficient evidence” to suggest these mouthwashes are a contributing factor. Not only does alcohol seem to make the mouth’s cells more vulnerable to cancer-causing agents, McCullough says “its first breakdown product is acetaldehyde, a known human carcinogen.” While alcohol is mostly metabolized in the liver, they argue the breakdown process actually begins in the oral cavity. “Excessive mouthwash use, over a long period of time, will increase the amount of acetaldehyde in the mouth,” McCullough says.
His hypothesis is nothing new: experts have raised the possibility these mouthwashes could be a cancer risk for over two decades. A 2007 study in the American Journal of Epidemiology, for instance, concluded that daily mouthwash use was a risk factor for head and neck cancer, independent of tobacco or alcohol consumption (McCullough draws on this study in his paper). A 2008 study of patients in Brazil linked its daily use to oral cancer.
Many of the blue and green bottles on store shelves contain more alcohol than wine or beer. Scope Original Mint is 15 per cent alcohol, for example, while Listerine Fresh Burst—the company’s most popular mouthwash—is 22 per cent. Alcohol is included as a solvent for active ingredients and flavours, preservative, and antiseptic, says Melissa Karis of Procter & Gamble Canada. (Some, like Crest Pro-Health Rinse, do not contain alcohol.)
McCullough’s paper has been, to put it mildly, controversial. Soon after it was published, Laurence Walsh, a professor of dental science at the University of Queensland, fired back in a letter to the ADJ: “There is no doubt that the real villain in the oral cancer story is ingested alcohol from beverages.” Alcoholic drinks create “prolonged and repeated exposures,” while mouthwash is swished around the mouth for seconds only, he writes. Walsh also found several flaws in the 2007 study McCullough cites in his review, ranging from “inconsistent questionnaires” to limited data.
Sol Silverman, a professor of oral medicine at the University of California, San Francisco, believes alcohol-containing mouthwashes are safe for everyone except children and recovering alcoholics. Not only did the U.S. Food and Drug Administration take a look at them over 10 years ago; the theory that acetaldehyde is produced in the mouth is “speculation,” he says. Finally, he adds, the Australian paper was a review of previous research, and contains no new data.
Mouthwash makers have also moved to defend their product. Gerry Wright is senior director, regulatory affairs for Johnson & Johnson Inc., which manufactures Listerine, Canada’s leading brand. He calls Listerine “the most extensively tested mouthwash in the world, with over 30 well-controlled studies demonstrating its safety,” and notes that it’s been used “by over one billion people for more than 100 years.” Even the Australian Dental Association, publisher of the ADJ, quickly distanced itself from McCullough’s paper, and continues to give its Seal of Approval (which promotes oral health products to consumers) to several mouthwashes that contain alcohol. The Canadian and American Dental Associations do the same. The CDA’s committee on clinical and scientific affairs will take a closer look at the Australian review at a future meeting, says Euan Swan, the CDA’s manager of dental programs. For now, though, “if people are using an alcohol-based mouthwash, there’s no reason to stop.”
Others are not so sure. Dr. Martin Corsten is chairman of the department of otolaryngology at the Ottawa General Hospital. “I think it would be reasonable to avoid alcohol-containing mouthwashes, especially if you smoke,” he says. But Swan insists that old bathroom routine—brush, floss, gargle, spit—is perfectly safe: “I have Listerine at home, and I use it.”