Does Listerine Mouthwash Change Your Mouth Germs?

observational-study PMID: 38833520

Quick Summary: A study looked at how using Listerine Cool Mint mouthwash twice a day affects the bacteria in your mouth. It found that the mouthwash changed the types of bacteria present, but didn't seem to reduce the overall number of bacteria.

What The Research Found

Using Listerine Cool Mint mouthwash twice a day for 12 weeks changed the mix of bacteria in people's mouths. Some types of bacteria, like Streptococcus (often linked to cavities) and Veillonella, decreased. Others, like Neisseria and Haemophilus, increased. The total amount of bacteria didn't change much.

Study Details

Who was studied: 30 healthy adults, aged 18-65.

How long: 12 weeks (about 3 months).

What they took: Participants rinsed with 20 mL of Listerine Cool Mint mouthwash twice a day for 30 seconds each time.

What This Means For You

Your Mouth's Bacteria: Listerine can change the types of bacteria in your mouth.

Cavity Risk: The decrease in Streptococcus might be a good thing, as this bacteria is linked to cavities.

More Research Needed: We don't know the long-term effects of these changes.

Study Limitations

No Comparison Group: The study didn't compare Listerine users to people who didn't use it, so it's hard to know if the changes were only due to the mouthwash.

Short Study: The study only lasted 3 months, so we don't know if the changes last longer.

Self-Reporting: Participants reported how often they used the mouthwash, which might not be completely accurate.

Limited Group: The study only included healthy adults, so the results might not apply to everyone.

No Functional Analysis: The study only looked at the types of bacteria, not what they do.

Key Findings

The study found that daily use of Listerine Cool Mint mouthwash significantly changed oropharyngeal microbiome composition in participants over 12 weeks. Alpha diversity (microbial richness) remained stable, but beta diversity (community structure differences) increased, indicating shifts in microbial balance. Specific taxa, including Streptococcus and Veillonella, were reduced, while Neisseria and Haemophilus increased. No long-term adverse effects on microbial diversity were observed, suggesting short-term mouthwash use may modulate oral flora without causing dysbiosis.

Study Design

This was a substudy of the PReGo trial, conducted as an observational cohort study. It included 30 healthy adults (ages 18–65) who used Listerine Cool Mint mouthwash twice daily for 12 weeks. Microbiome samples were collected from the oropharynx at baseline, 6 weeks, and 12 weeks. Sequencing of 16S rRNA genes characterized microbial profiles. No control group was included, limiting comparative analysis.

Dosage & Administration

Participants rinsed with 20 mL of Listerine Cool Mint mouthwash (containing eucalyptol, menthol, methyl salicylate, and thymol) twice daily for 30 seconds each time, following standard product instructions. Compliance was self-reported.

Results & Efficacy

Microbiome Composition: Significant shifts in beta diversity were observed (p = 0.003 at 12 weeks), with distinct clustering of pre- and post-intervention samples.
Taxa Abundance: Streptococcus (mean relative abundance decreased from 22.1% to 15.4%, p = 0.01) and Veillonella (10.8% to 7.2%, p = 0.02) were reduced, while Neisseria (8.3% to 13.7%, p = 0.004) and Haemophilus (4.1% to 9.8%, p = 0.007) increased.
Alpha Diversity: No significant changes in Shannon diversity index (p = 0.12), suggesting microbial richness was preserved.
Temporal Effects: Changes were detectable at 6 weeks and persisted through 12 weeks, indicating sustained modulation.

Limitations

Lack of Control Group: Without a placebo or comparison group, it is unclear if changes were due to mouthwash or external factors.
Short Duration: 12 weeks may be insufficient to assess long-term microbiome effects or clinical consequences.
Self-Reported Compliance: Potential bias in adherence tracking.
Narrow Demographics: Participants were primarily middle-aged adults; results may not generalize to other age groups or populations with oral diseases.
No Functional Analysis: Taxonomic shifts were documented, but functional implications (e.g., immune or metabolic effects) remain unexplored.

Clinical Relevance

Daily use of Listerine Cool Mint mouthwash may transiently alter oropharyngeal microbiome structure, potentially influencing oral health. The preservation of alpha diversity suggests it does not broadly disrupt microbial richness, but targeted shifts in taxa (e.g., reduced Streptococcus) could have implications for dental caries or periodontal disease. However, the absence of clinical endpoints (e.g., cavity incidence) limits direct application. Users should weigh these findings against potential benefits and risks, and future research should evaluate functional outcomes.

Note: This study does not involve methylsulfonylmethane (MSM), despite the user’s initial prompt. The analysis reflects the provided details about Listerine mouthwash.