Effects of Mouthwashes on the Oral Microbiome and Systemic Health

February 11, 2026 updated by: Mimoza Cana-Bishop, University of Plymouth

OVERVIEW

While antimicrobial mouthwashes are proven to be clinically effective for management of certain oral microbial diseases, recent studies suggest tha, in addition to targeting bacteria responsible for gum diseases such as gingivitis and periodontitis, they may harm healthy bacteria and disturb the balance and protective role of the oral microbiome (dysbiosis).

Most findings on the oral microbiome and mouthwashes involve chlorhexidine use, demonstrating that it may induce dysbiosis and compromise the host oral microenvironment . A recent study completed in 2025 has shown that CPC mouthwash can also inhibit nitrate synthesis in the mouth. However there remains a need for further research on other agents used in mouthrinses, such as hydrogen peroxide, essential oils, to determine whether their clinical effectiveness in managing oral disease is accompanied by changes to the oral microbiome. In dentistry, despite this being the place where most people are treated, there are very few research studies that have been performed in primary care settings. Hence this study will be designed for delivery in primary care, to produce 'real-life' data on a patient cohort more typical of general dental practice.

This PhD project will select several of the most commonly used over the counter (OTC) mouthwash constituents, used by the general public, that have a limited evidence base, regarding their effects on the oral microbiome in vivo. . All mouthwashes will be tested in people with, or without, gum disease (gingivitis and periodontitis) to determine which interventions are best used in either health or disease.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Not yet recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

Detailed Description

PROJECT AIMS

The aim of this project is to determine the role of different mouthwashes on the oral microbiome and its relationship with cardiovascular health. We will achieve this by conducting a double-blinded randomised clinical trial (pilot study) in a primary care dental setting, to investigate (i) the composition of the oral microbiome in different oral niches in periodontal health and disease, and (ii) determine how the oral microbiome is altered by the use of different mouthwashes during oral health and disease, with either , essential oil (EOs), CPCs, hydrogen peroxide (H2O2); all versus placebo (water or saline).

OVERVIEW

While antimicrobial mouthwashes are proven to be clinically effective for management of certain oral microbial diseases, recent studies suggest that, in addition to targeting bacteria responsible for gum diseases such as gingivitis and periodontitis, they may harm healthy bacteria and disturb the balance and protective role of the oral microbiome (dysbiosis).

Study Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
200

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Early Phase 1

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

  • Inclusion & Exclusion

All individuals aged 18 years and older will be eligible to take part in this study. Exclusion will apply to individuals who:

Are current smokers, due to the well-documented impact of smoking on oral and systemic health.

Have a known diagnosis of hypertension, diabetes, or cancer, as these systemic conditions may influence oral microbiome and inflammatory responses.

Have taken a course of antibiotics within the last three months, since antibiotics are known to disrupt microbial balance and may confound the interpretation of oral microbiome data.

Report allergies to essential oils or to milk proteins, as these ingredients may be present in the study mouthwash and could trigger adverse reactions.

In addition, participants who have never previously used a mouthwash will be excluded. This is a precautionary measure designed to avoid even the minimal possibility of adverse responses.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Prevention
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: Triple

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: mouthwashes

Population

This study aims to recruit up to 200 participants over a period of thr years on a part-time basis. Recruitment will be carried out through three sites: (i) the University of Plymouth campus population (as successfully used in earlier studies such as Bescos et al., 2020), (ii) the Peninsula Dental School / Peninsula Dental Social Enterprise (PDSE) triage patient clinics (non-NHS clinics), and (iii) the Southside Dental Practice, a private primary care practice located in Southsea, Portsmouth.

Sample size was calculated using G*Power software, which showed that usually 20-30 participants per group are enough, depending on whether the focus is clinical outcomes, blood markers, or microbiome changes.

For this project, the main outcome is clinical effectiveness, measured through changes in plaque and bleeding scores.

The PDSE clinics collectively see around 400 patients per day across their sites, providing a large and diverse pool of potential participants. In comparis
Drug: Use of mouthwashes

Population

This study aims to recruit up to 200 participants over a period of 3 years on a part-time basis. Recruitment will be carried out through three sites: (i) the University of Plymouth campus population (as successfully used in earlier studies such as Bescos et al., 2020), (ii) the Peninsula Dental School / Peninsula Dental Social Enterprise (PDSE) triage patient clinics (non-NHS clinics), and (iii) the Southside Dental Practice, a private primary care practice located in Southsea, Portsmouth.

Sample size was calculated using G*Power software, which showed that usually 20-30 participants per group are enough, depending on whether the focus is clinical outcomes, blood markers, or microbiome changes.

For this project, the main outcome is clinical effectiveness, measured through changes in plaque and bleeding scores.

The PDSE clinics collectively see around 400 patients per day across their sites, providing a large and diverse pool of potential participants. In compariso
Experimental: placebo

Population

This study aims to recruit up to 200 participants over a period of 3 years on a part-time basis. Recruitment will be carried out through three sites: (i) the University of Plymouth campus population (as successfully used in earlier studies such as Bescos et al., 2020), (ii) the Peninsula Dental School / Peninsula Dental Social Enterprise (PDSE) triage patient clinics (non-NHS clinics), and (iii) the Southside Dental Practice, a private primary care practice located in Southsea, Portsmouth.

Sample size was calculated using G*Power software, which showed that usually 20-30 participants per group are enough, depending on whether the focus is clinical outcomes, blood markers, or microbiome changes.

For this project, the main outcome is clinical effectiveness, measured through changes in plaque and bleeding scores.

The PDSE clinics collectively see around 400 patients per day across their sites, providing a large and diverse pool of potential participants. In comparis
Drug: Use of mouthwashes

Population

This study aims to recruit up to 200 participants over a period of 3 years on a part-time basis. Recruitment will be carried out through three sites: (i) the University of Plymouth campus population (as successfully used in earlier studies such as Bescos et al., 2020), (ii) the Peninsula Dental School / Peninsula Dental Social Enterprise (PDSE) triage patient clinics (non-NHS clinics), and (iii) the Southside Dental Practice, a private primary care practice located in Southsea, Portsmouth.

Sample size was calculated using G*Power software, which showed that usually 20-30 participants per group are enough, depending on whether the focus is clinical outcomes, blood markers, or microbiome changes.

For this project, the main outcome is clinical effectiveness, measured through changes in plaque and bleeding scores.

The PDSE clinics collectively see around 400 patients per day across their sites, providing a large and diverse pool of potential participants. In compariso

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
effect of mouthwashes on oral microbiome
Time Frame: three years

EXPECTED OUTCOMES / DELIVERABLES

One of the main expected outcomes of this study is to provide clear evidence on the clinical effectiveness of commonly used mouthwashes and their effect on oral microbiome and cardiovascular health. It is anticipated that some mouthwashes will significantly reduce dental plaque and bleeding on probing when compared with placebo. Demonstrating these effects will help confirm which products can genuinely support daily oral hygiene and clinical treatment of gum conditions, alongside either beneficial or no effects on the oral microbiome, such that their beneficial effects do not outweigh the risks.

In participants with good oral health, we thus expect that effective mouthwashes will not only reduce plaque but also maintain a balanced oral microbiome. This means that mouthwashes should support microbiome health, without causing dysbiosis or loss of diversity.

In participants with gingivitis or periodontal disease, the expectation is that mouthwash
three years

Secondary Outcome Measures

Secondary Outcome Measures

In a clinical study's protocol, a planned outcome measure that is not as important as the primary outcome measure for evaluating the effect of an intervention but is still of interest. Most clinical studies have more than one secondary outcome measure.
Outcome Measure
Measure Description
Time Frame
effect of mouthwashes on cardiovascular health
Time Frame: three years

EXPECTED OUTCOMES / DELIVERABLES

One of the main expected outcomes of this study is to provide clear evidence on the clinical effectiveness of commonly used mouthwashes and their effect on oral microbiome and cardiovascular health. It is anticipated that some mouthwashes will significantly reduce dental plaque and bleeding on probing when compared with placebo. Demonstrating these effects will help confirm which products can genuinely support daily oral hygiene and clinical treatment of gum conditions, alongside either beneficial or no effects on the oral microbiome, such that their beneficial effects do not outweigh the risks.

In participants with good oral health, we thus expect that effective mouthwashes will not only reduce plaque but also maintain a balanced oral microbiome. This means that mouthwashes should support microbiome health, without causing dysbiosis or loss of diversity.

In participants with gingivitis or periodontal disease, the expectation is that mouthwash
three years

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
University of Plymouth

Investigators

Investigators

A researcher involved in a clinical study. Related terms include site principal investigator, site sub-investigator, study chair, study director, and study principal investigator.
  • Study Director: zoe Brookes, PhD, University of Plymouth

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

  • References Al-Maweri, S. A., et al. (2025). "The association between the oral microbiome and hypertension: a systematic review." Journal of oral microbiology 17(1): 2459919. Alrashdan, M. S., et al. (2023). "The Effects of Antimicrobial Mouthwashes on Systemic Disease: What Is the Evidence?" International dental journal 73: S82-S88 Aravinth, V., et al. "Comparative evaluation of saltwater rinse with chlorhexidine against oral microbes: a school-based randomized controlled trial " Indian Soc Pedod Prev Dent, 35 (4) (2017), pp. 319-326 Bescos, R., et al. "The comparative effect of propolis and chlorhexidine mouthwash on oral nitrite-producing bacteria and blood pressure regulation." Bescos, R., et al. (2020). "Effects of Chlorhexidine mouthwash on the oral microbiome." Sci Rep 10(1): 5254-5254. Bondonno, C. P., et al. (2015). "Antibacterial Mouthwash Blunts Oral Nitrate Reduction and Increases Blood Pressure in Treated Hypertensive Men and Women." Am J Hypertens 28(5): 572-575. Brookes, Z., et al. (2023). "Antimicrobial Mouthwashes: An Overview of Mechanisms-What Do We Still Need to Know?" International dental journal. Brookes, Z., et al. (2023). "Mouthwash Effects on the Oral Microbiome: Are They Good, Bad, or Balanced?" International dental journal. Burcham, Z. M., et al. (2020). "Patterns of Oral Microbiota Diversity in Adults and Children: A Crowdsourced Population Study." Scientific reports 10(1): 2133. Burton, J. P., et al. (2006). "preliminary study of the effect of probiotic Streptococcus salivarius K12 on oral malodour parameters." Journal of Applied Microbiology 100(4): 754-764. Casarin, M., et al. (2023). "Effect of mouthwashes on gingival healing after surgical procedures: A systematic review." European Journal of Oral Sciences 131(3): e12931-n/a. Caselli, E., et al. (2020). "Defining the oral microbiome by whole-genome sequencing and resistome analysis: the complexity of the healthy picture." BMC Microbiol 20(1): 120-120

Helpful Links

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Estimated)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
February 1, 2026

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
February 1, 2028

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
March 1, 2029

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
January 12, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
January 12, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
January 21, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
February 17, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
February 11, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
January 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • University of Plymouth

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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