Effects of Mouthwashes on the Oral Microbiome and Systemic Health

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: Not yet recruiting
• Conditions: Hypertension
• Intervention / Treatment: Drug: Use of mouthwashes

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: Interventional
• Enrollment (Estimated): 200
• Phase: Early Phase 1

Contacts and Locations

• Study Contact: Name: mimoza cana-bishop, MSc; Phone Number: +447903995399; Email: mimoza.cana-bishop@plymouth.ac.uk
• Study Contact Backup: Name: Zoe Brookes, PhD; Phone Number: 441752586828; Email: zoe.brookes@plymouth.ac.uk

Participation Criteria

Eligibility Criteria

• 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

How is the study designed?

Design Details

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

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
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

Outcome Measure	Measure Description	Time Frame
effect of mouthwashes on oral microbiome	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

Outcome Measure	Measure Description	Time Frame
effect of mouthwashes on cardiovascular health	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

• Sponsor: University of Plymouth
• Investigators: Study Director: zoe Brookes, PhD, University of Plymouth

Publications and helpful links

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

• Library of Plymouth university that covers the main databases

Study record dates

Study Major Dates

• Study Start (Estimated): February 1, 2026
• Primary Completion (Estimated): February 1, 2028
• Study Completion (Estimated): March 1, 2029

Study Registration Dates

• First Submitted: January 12, 2026
• First Submitted That Met QC Criteria: January 12, 2026
• First Posted (Actual): January 21, 2026

Study Record Updates

• Last Update Posted (Actual): February 17, 2026
• Last Update Submitted That Met QC Criteria: February 11, 2026
• Last Verified: January 1, 2026

More Information

Terms related to this study

• Keywords: Oral microbiome dysbiosis
• Additional Relevant MeSH Terms: Vascular Diseases; Cardiovascular Diseases; Hypertension
• Other Study ID 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