New Study Tests Cinnamon, Eucalyptus And Green Tea Extracts Against Oral Bacteria

A new lab study tested green tea vs chlorhexidine, along with cinnamon and eucalyptus extracts, against two oral bacteria. Published November 9, 2026, in Scientific Reports, it found chlorhexidine the strongest agent. Green tea and cinnamon also slowed bacterial growth in culture. None of the results come from patients.

TL;DR

• Researchers in Iran tested three plant extracts against Streptococcus mutans and Streptococcus sanguinis in the lab

• Chlorhexidine stopped growth at 2 to 4 µg/mL, while cinnamon needed 187 to 375 µg/mL

• Green tea ranked second, and cinnamon third, and eucalyptus received no ranking in the abstract

• Adding an efflux pump inhibitor widened some inhibition zones, which points to a resistance mechanism worth studying

What Did The New Study Investigate?

Maryam Sadat Hashemipour, Elahe Sadeghi, and colleagues led the work, mainly from Kerman University of Medical Sciences in Iran. The team compared cinnamon, eucalyptus, and green tea extracts with chlorhexidine gluconate. The study was in vitro, so every test took place on cultured bacteria.

The researchers used two standard methods. Broth dilution found the minimum inhibitory concentration (MIC) of each agent. Agar well diffusion measured the clear zone each agent created around a well in a bacterial plate.

The two test organisms play very different roles in the mouth. Streptococcus mutans is the classic driver of caries because it turns sugar into acid and builds sticky biofilm. Streptococcus sanguinis is a common early colonizer of healthy tooth surfaces.

That difference matters at the chair. S. sanguinis competes with S. mutans for space and produces hydrogen peroxide that can hold it back. An ideal anti-caries agent would suppress S. mutans and leave S. sanguinis alone. Both agents with published MIC values stopped S. sanguinis at half the dose needed for S. mutans.

That pattern runs against current caries thinking. Modern prevention aims to shift the biofilm toward health-associated species. Wiping out every Streptococcus can clear space for the same acid producers to return. A botanical rinse that proved selective would earn real interest. This study gives no sign of that yet.

Which Extracts Showed The Strongest Antibacterial Activity?

The study ranked chlorhexidine first, followed by green tea and then cinnamon. The abstract reports MIC values for chlorhexidine and cinnamon only. MIC is the lowest tested concentration that stopped visible growth under the assay conditions. A lower number means stronger activity.

How Did Cinnamon Perform?

Cinnamon needed about 94 times more material than chlorhexidine to stop S. mutans. Its 375 µg/mL MIC equals 0.0375%, which sounds low. Plant extracts are mixtures, though, and their active compounds vary by species, harvest, and extraction method. Cinnamon's main antibacterial compound, cinnamaldehyde, is also a well-known cause of contact reactions in the mouth.

What Did Researchers Find About Green Tea?

Green tea ranked second, ahead of cinnamon, and the authors named it the most promising alternative. Its activity comes mainly from catechins, the polyphenols that also give tea its bitterness. A cup of tea does not deliver a standardized extract. This result says nothing about tea drinking and cavities.

Staining deserves a closer look here. Tea is a common source of extrinsic stain on its own. Chlorhexidine stain also forms partly when dietary chromogens, such as tea tannins, bind to chlorhexidine on the tooth surface. Patients on a chlorhexidine course who drink a lot of tea often stain fastest. A tea-based rinse could still carry its own staining problem. Only clinical testing can answer that.

What About Eucalyptus?

Eucalyptus oil was tested, but the abstract does not rank it or give its MIC. Readers should not assume it matched green tea or cinnamon. Its lab extract also differs from commercial essential oil rinses. Those pair eucalyptol with thymol, menthol, and methyl salicylate in a tested formula.

How Did Chlorhexidine Compare With The Plant Extracts?

Chlorhexidine served as the reference agent because it has decades of clinical data behind it. The study used 0.2% chlorhexidine, which equals 2,000 µg/mL. That is about 500 times its MIC for S. mutans.

Lab potency is only part of its clinical edge. Chlorhexidine binds to teeth and soft tissue and keeps releasing for hours after a rinse. This property, called substantivity, lets a 30-second rinse keep working. The plant extracts in this study were not tested for it. The guide to chlorhexidine in dentistry covers the clinical evidence in detail.

Exposure time explains why this matters. An MIC test leaves bacteria in a fixed concentration overnight. A rinse lasts 30 to 60 seconds, and saliva starts diluting and clearing it right away. An extract that needs 375 µg/mL of steady exposure in a tube may fall well short in a real mouth. Retention on oral surfaces, more than raw potency, decides whether a rinse works between brushings.

This was not a clinical trial of herbal mouthwash against a chlorhexidine product. US patients usually receive chlorhexidine at 0.12%, as in Peridex oral rinse, for short, targeted courses.

What Did The Efflux Pump Experiment Reveal?

Efflux pumps are protein channels in the bacterial membrane. They push unwanted substances, including antimicrobials, back out of the cell. A bacterium with active pumps can survive doses that should harm it.

The researchers repeated the tests with omeprazole, a stomach acid drug used here as a lab efflux pump inhibitor. Some inhibition zones grew wider once it was added. That suggests the pumps help these streptococci tolerate the agents tested.

The finding has research value. A review in Antibiotics lists efflux pump activity as a key mechanism behind chlorhexidine tolerance. Patients taking omeprazole for reflux should draw no conclusion about their mouth. Lab concentrations in a dish have no tested link to saliva levels in people taking the drug. Nobody should add omeprazole to a rinse, and the study never tested that in people.

Could Plant Extracts Become Alternatives To Chlorhexidine?

Interest in alternatives has a real clinical basis. Chlorhexidine stains teeth, changes taste, and speeds calculus buildup, so dentists rarely prescribe it long term. It also reshapes the oral microbiome.

In a study of 87 hospitalized patients, 5 to 7 days of chlorhexidine reduced oral bacterial diversity. Another systematic review adds that prolonged use can displace nitrate-reducing bacteria. It can also lower oral pH. Those bacteria help the body produce nitric oxide, which supports blood vessel function.

Clinical data on herbal rinses is still thin. A review in the Scientific Dental Journal found herbal mouthwashes broadly comparable to chlorhexidine. It looked at plaque and gum measures. It drew on only five clinical studies and called for long-term safety data.

Formulation also shapes results. A dental hygiene meta-analysis compared essential oil rinses with and without alcohol. The alcohol-free versions controlled plaque less well. The same active oils performed differently in a different base.

The patients with the most to gain are easy to name. Orthodontic patients, people with dry mouth, and older adults with root caries often need antimicrobial support for months. Chlorhexidine side effects limit its use in exactly those groups. A tolerable botanical rinse with proven retention would fill that slot.

Before a plant-based rinse replaces chlorhexidine for any indication, the evidence has to catch up. Researchers would need a standardized extract and a stable formula. They would also need cell toxicity data and randomized trials lasting at least six months. Those trials should measure plaque and gingival scores, staining, and caries outcomes. The guide to mouthwash for gingivitis explains how rinses earn clinical recommendations today.

What Should Patients Know Before Making Herbal Rinses At Home?

Lab results like these often reach patients as a reason to mix their own rinses. Concentrated botanicals carry real risks, and clinicians see the damage in the chair.

• Cinnamon oil can cause painful contact stomatitis, with red, peeling, or ulcerated tissue

• Undiluted essential oils can burn the gums and cheek lining

• Eucalyptus oil is toxic if swallowed, and small amounts are dangerous for children

• Homemade mixes have no fixed strength, so two batches can behave very differently

The ADA advises that children under 6 should not use mouthrinse unless a dentist directs it. Antibacterial activity alone cannot rebuild lost gum tissue, as the guide to home remedies for gum recession explains.

A common chairside question is whether a prescribed chlorhexidine course can be swapped for green tea. The answer depends on why it was prescribed. After periodontal surgery or deep cleaning, the course should be finished as directed. Once it ends, a commercial botanical rinse is a reasonable adjunct for patients who want one.

Patients who prefer botanical products can use them safely with a few habits. They should pick a commercial product with clinical data and bring it to their next visit. Brushing with fluoride toothpaste stays non-negotiable. The best dental rinse for gums guide compares formulated products by concern. Noting the chosen rinse in the dental treatment plan lets the team check gum health against it at recall.

What Are The Study's Limitations?

The study answers a narrow lab question, and several limits apply.

• All testing took place in vitro on cultured bacteria

• Only two bacterial species were tested

• No patients used any rinse

• No cavities, plaque scores, or gingivitis outcomes were measured

• Extract composition and concentration affect how results compare

• Single-species cultures behave differently from multispecies oral biofilms

• No long-term safety or product stability data were collected

• The efflux pump experiment does not show any clinical benefit

Bacteria in mature plaque biofilm can tolerate far higher concentrations than free-floating cells in a test tube. The article is also an early accepted manuscript, so figures may change in the final version.

Bottom Line

Green tea and cinnamon extracts slowed the growth of two oral streptococci in the lab, but chlorhexidine remained far more potent. The efflux pump findings point to a mechanism worth studying. None of this shows that herbal rinses prevent cavities or treat gum disease in patients. Fluoride, mechanical cleaning, and prescribed rinses remain the evidence-based tools, and the guide to preventing cavities covers them.

This article is for informational purposes only and does not constitute medical advice. Always consult with qualified healthcare professionals for diagnosis and treatment recommendations specific to your situation.