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Study Links Mouthwash to Cancer-Causing Bacteria

Alcohol-based mouthwash may disrupt the oral microbiome, potentially increasing the risk of periodontal diseases and even cancer, a new study finds.

Nearly 200 million Americans use mouthwash. It can be a helpful addition to daily oral hygiene, as it helps reach areas not easily accessed by a toothbrush, according to the American Dental Association. Mouthwash can be used to prevent tooth decay, plaque and gingivitis, and bad breath, among other issues.

However, a new study published in the Journal of Medical Microbiology suggests that the daily use of alcohol-based mouthwash may disrupt the oral microbiome.

The study was part of the Preventing Resistance in Gonorrhoea trial, which includes men who have sex with men taking HIV pre-exposure prophylaxis (PrEP).

In the trial, 59 participants received three months of daily Listerine Cool Mint followed by three months of placebo mouthwash or vice versa. Swabs from their oropharynx were taken and analyzed at the beginning of the study and after three months of use of each mouthwash.

The study found that Fusobacterium nucleatum and Streptococcus anginosus were significantly more abundant after Listerine use.

Camille Zenobia, Ph.D., a microbiologist, says previous studies have linked over-the-counter alcohol-based mouthwashes to increased risk of diabetes and cardiovascular disease.

Scientists think disruption to the oral microbiome by these products alters the nitric oxide cycle that is needed for healthy blood pressure and metabolic health.

Alcohol-based mouthwashes have been implicated in oral cancer, Zenobia says. However, the research studies on mouthwash vary in quality and clinical parameters resulting in conflicting results.

We know that, in general, the use of alcohol or antibacterial medication over long periods can impact our health in many ways. I think we should consider limiting the use of both ingredients in our oral care products as a precautionary measure.


Bruno Lima, DDS, Ph.D., an assistant professor at the University of Minnesota, says the study does not provide enough data to make generalized conclusions, given the small sample size of only 32 participants and the focused population, which is men who have sex with men and are on PreP. However, he calls the findings interesting and says they warrant further investigation.

Zenobia calls the increased abundance of S. anginosus and F. nucleatum in this study concerning.

F. nucleatum, the bacteria normally found in the mouth, has been strongly implicated as a potential contributor to colorectal cancer growth: increased amounts of it have been found in the intestines of people with colorectal tumors compared with people without cancer.

Zenobia points out that F. nucleatum is also strongly associated with periodontal disease and has been found to disrupt gut health, although the bacterium can be helpful in some cases. Meanwhile, S. anginosus has been linked to gastric cancer and colorectal cancers.

Lima says scientists are still learning about the link between a few cancers F. nucleatum and S. anginosus.

“The link between the oral prevalence of these bacteria and cancer development at non-oral sites needs to be developed further,” he adds.

Zenobia says, “In general, I think we should be concerned that our oral hygiene products may be altering our microbiome in significant ways and we should be looking for products that help us clean off excess buildup while maintaining a balance with our microbial communities.”

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