Kenvue challenges study linking Listerine Cool Mint to “damaging effect on oral microbiome”

05 Jul 2024 --- A study published in the Journal of Medical Microbiology finds that while Listerine Cool Mint effectively targets dental plaque and gingivitis, its impact on the broader oropharyngeal microbiome should be carefully evaluated. Personal Care Insights talks to Chris Kenyon, study author and head of the STI unit at the Institute of Tropical Medicine in Antwerp, Belgium, and the parent company of Listerine Cool Mint, Kenvue, who disagrees with the research.

The research flags potential concerns regarding the regular use of Listerine Cool Mint. It suggests product use correlates with an increase in opportunistic bacteria “previously reported to be enriched in periodontal diseases, oesophageal and colorectal cancer and systemic diseases.”

The FMCG company challenges the findings and stands by its product:

“Studies on the impact of Listerine on oral health have been published in hundreds of peer-reviewed publications for more than a century, making it one of the most extensively tested mouthwash brands in the world. We continuously evaluate the latest science and monitor safety signals to evaluate the benefit-risk profile of our products. Listerine is safe when used as directed on the label, and there is no evidence that Listerine causes cancer.”

“After a thorough scientific review, we found the paper exhibits several methodological issues that call into question its results. The findings in this paper do not provide evidence of any adverse health effect, lacking several important design controls and adequate rigor to make any conclusions about potential impact on human health.”

The company says Listerine is clinically proven to be five times more effective than flossing for plaque reduction above the gum line.

Kenvue found the paper showed methodological issues that called into question its results (Image credit: Kenvue).Listerine Cool Mint’s long-term impact
The study focused on men who have sex with men, taking HIV pre-exposure prophylaxis as part of the Preventing Resistance in Gonorrhoea trial.

Kenyon says “Listerine Cool Mint led to an increase in Neisseria gonorrhoeae infections. We speculated this was due to its damaging effect on the oral microbiome, which in turn decreased natural resistance to the infection.”

“We think short-term use for treating gingivitis is safe but think that long-term use may be harmful and advise against this unless there are compelling indications.”

The study examined the daily use of mouthwash, which has long been hailed. However, researchers question its broader impact on the oral microbiome, looking at changes in the composition of the oropharyngeal microbiome.

Kenyon says short-term use of Listerine Cool Mint for treating gingivitis is safe but long-term use may be harmful.“Significant” change in oral microbiome
The study found that using Listerine Cool Mint caused significant changes in the oropharyngeal microbiome. Streptococcus (61.7 %) was the most frequently found genus in the samples, followed by Veillonella (10%) and Prevotella (13.5%).

After three months of Listerine use, there was a “significant” change in the oral microbiome composition at the genus level (P = 0.006). Specifically, Fusobacterium nucleatum and Streptococcus anginosus showed increased numbers compared to baseline levels.

Kenyon suspects “Fusobacterium nucleatum and Streptococcus anginosus were increased in abundance due to the high alcohol content of the product.”

Participants used Listerine Cool Mint mouthwash or a placebo for three months each as part of a double-blind, crossover, randomized controlled study. Oropharyngeal swabs were taken at the beginning and end of the mouthwashing process. The microbial DNA extracted from these swabs was analyzed using shotgun metagenomic sequencing.

Regarding implications for daily Listerine users, Kenyon says, “Long-term studies would be required to define these risks but based on the precautionary principle, we advise against long-term use until studies have clearly demonstrated safety.”

“Look after your oral microbiome by not taking substances that can damage it,” he urges.

By Venya Patel

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