Mouthwash, Mouth Bacteria and Nitric Oxide: What the Evidence Says About Blood Pressure and Blood Sugar

Key takeaways

• Nitrate from vegetables is concentrated into your saliva, and tongue and saliva bacteria such as Rothia and Neisseria reduce it to nitrite, the one step in the nitric oxide pathway that human cells handle poorly [1][2][3].
• Chlorhexidine 0.2% rinse cuts nitrate-reducing bacteria by roughly 80 percent and lowers salivary nitrite in every trial that has measured it; a 36-person crossover also found it made saliva more acidic [4][5].
• Alcohol-based essential-oil rinses also thin out the oral community: in a four-week trial, twice-daily use lowered bacterial diversity and reduced about 55 to 60 species, including nitrate-reducing Veillonella, Haemophilus and Neisseria; the alcohol-free version of the same formula reduced eight [31].
• Across four short trials of chlorhexidine, two found systolic blood pressure rose about 2 to 3 mmHg, one found no change, and one found responses in both directions. All had 15 to 27 participants and lasted a week or less [5][6][7][8].
• Essential-oil rinses behaved like a control rinse in the one head-to-head comparison; no trial has shown a blood pressure effect from an essential-oil mouthwash [9].
• The headline figures linking mouthwash to hypertension and prediabetes come from one Puerto Rican cohort that did not record the type of mouthwash, did not measure the proposed mechanism, and has not been replicated [10][11].
• Four randomized trials of nitrate or beetroot juice in type 2 diabetes found no improvement in insulin sensitivity, blood glucose or HbA1c [12][13].
• Gum disease lowers the mouth's nitrate-reducing capacity, and periodontal treatment restores it within about 90 days [14].

How a salad becomes nitric oxide

Nitric oxide keeps blood vessels relaxed and blood flowing. Most of it is made inside the vessel wall from an amino acid, but there is a second supply route that runs through your mouth [1].

When you eat nitrate-rich vegetables (arugula, spinach, lettuce, beets), nitrate is absorbed from the gut into the blood. About a quarter of it is then pulled back out by the salivary glands and pumped into saliva, where its concentration can reach roughly twenty times the level in blood [2][3]. Bacteria living on the tongue and in saliva carry an enzyme, nitrate reductase, that converts some of that nitrate to nitrite. You swallow the nitrite, and stomach acid, blood and tissue enzymes turn it into nitric oxide [1][3].

The reason the detour exists is that human cells reduce nitrate poorly. The bacterial step is the bottleneck. Once nitrite exists, the body can finish the job on its own [1][2].

Which bacteria matter has become clearer. In an 18-person randomized crossover, ten days of nitrate-rich beetroot juice raised Neisseria by 351 percent and Rothia by 127 percent while lowering Prevotella and Veillonella, and people with more Rothia and Neisseria had higher nitrite in their blood [15]. These are not "good" and "bad" bacteria in the usual sense; they are species that happen to do this particular job well or poorly. The amount of bacteria matters less than you might expect: once a functional minimum is present, having more of them raised nitrite in saliva but not in blood [16].

What chlorhexidine does to this pathway

Chlorhexidine is the prescription antiseptic rinse used after gum surgery and during periodontal treatment. Its effect on the oral step is one of the more reproducible findings in this field. A single rinse reduces nitrate-reducing bacteria by about 80 percent and nearly abolishes the mouth's ability to convert nitrate for several hours; counts and function recover within six to eight hours, which is why twice-daily use is needed to sustain the effect [4][8]. In a 36-person crossover, seven days of chlorhexidine lowered both salivary and blood nitrite, and also made saliva more acidic and less able to buffer acid, with higher lactate [5]. That acidification is worth knowing about for its own sake, since acid is what drives cavities.

What about alcohol-based rinses?

Most over-the-counter antiseptic rinses are essential-oil formulas, and the classic versions carry 20 to 27 percent alcohol. They are not chlorhexidine, but they are not inert either.

In a four-week randomized trial of 121 adults with mild gum inflammation, twice-daily use of an alcohol-based essential-oil rinse lowered the diversity and richness of the oral community and reduced roughly 55 to 60 bacterial species compared with a control rinse, among them Veillonella, Haemophilus and Neisseria, three of the genera that reduce nitrate. An alcohol-free version of the same essential-oil formula reduced eight species, and a prototype with alcohol but a different base reduced about 40 [31]. The study was funded by the manufacturer, and the authors frame the effect as a "reset" of a gingivitis-type community rather than harm, but the direction is clear: alcohol-based rinses broadly suppress bacteria, and they do not spare the useful ones.

The one independent long-term trial points the same way, with a caveat. Fifty-nine adults used an alcohol-based essential-oil rinse daily for three months in a crossover against placebo. Two species rose significantly, Fusobacterium nucleatum and Streptococcus anginosus, both associated with gum disease and, in the lab, with some cancers. The caveat is that the placebo rinse also shifted the community significantly, the participants were a narrow group (men taking HIV prevention medication), and no health outcome was measured [32]. The authors' conclusion was that daily use "should be carefully considered," not that it causes disease.

What these studies have not shown matters as much. No trial has measured salivary nitrite or blood pressure after an alcohol-based rinse, and in the one study that compared products side by side, the essential-oil rinse behaved like water on both measures [9]. So "alcohol-based rinses disrupt the oral microbiome" is supported; "alcohol-based rinses raise blood pressure" is not. Two practical points are better established: alcohol dries the mouth, which is why the ADA suggests alcohol-free rinses for anyone with dry mouth [28], and the large pooled analyses have not found that mouthwash, alcohol-containing or otherwise, independently causes oral cancer [30].

Does it raise blood pressure?

Here the evidence is thinner, and the trials disagree.

Every trial was small and short, and none was designed to measure a hard outcome such as a heart attack. The authors of the positive hypertensive trial called the change "a small elevation" [7]. The pattern (a robust effect in saliva, a fragile effect in blood, a fragile effect on pressure) suggests chlorhexidine's influence on blood pressure sits near the limit of what trials this size can detect [17].

For scale, the same pathway run in the other direction is better established: a meta-analysis of 16 randomized crossover trials found that dietary nitrate lowers systolic blood pressure by about 4.4 mmHg, with a larger effect at higher doses [18]. Chlorhexidine's effect, where it appears, is roughly half that size and is the same lever pulled backward.

Two details matter for anyone reading this at home. First, the effect appears specific to chlorhexidine and possibly to cetylpyridinium chloride, the antiseptic in some over-the-counter rinses. In the one trial that compared products directly, blood pressure four hours after rinsing was 2 to 5 mmHg higher after chlorhexidine and after a cetylpyridinium rinse than after water, while an essential-oil rinse grouped with water [9]. No trial has found a blood pressure effect from an essential-oil mouthwash, and a 2025 pilot of cetylpyridinium found total salivary nitrite unchanged [19]. Second, who you are seems to matter. In the 2019 trial, people who habitually cleaned their tongue rose the most, while people who never cleaned it actually fell, which the authors tied to differences in which bacteria dominated [8]. That finding comes from one study with self-reported habits and should be read as a hypothesis.

The hypertension and diabetes headlines: one cohort, no product names

The figures that circulate online (mouthwash users have 85 percent more hypertension, 55 percent more prediabetes) come from the San Juan Overweight Adults Longitudinal Study, a cohort of overweight Hispanic adults in Puerto Rico followed for about three years [10][11]. Among 540 people without hypertension at the start, those using over-the-counter mouthwash at least twice a day had an incidence rate ratio of 1.85 for developing it (95% CI 1.17 to 2.94) [10]. The diabetes paper, from the same cohort, reported a ratio of 1.55 (95% CI 1.21 to 1.99) for prediabetes or diabetes [11].

Four problems keep these numbers from supporting a warning. The type and brand of mouthwash were never recorded, and twice-daily over-the-counter rinsing in this population overwhelmingly means essential-oil or cetylpyridinium products, the category the trial evidence suggests does not block nitrate reduction [20]. The proposed mechanism was never measured; no one tested the participants' saliva. People who are developing diabetes or heart disease tend to have more gum disease and are more often told to rinse, so the arrow may point the other way. And use below twice a day showed no association at all, an irregular dose-response that the American Diabetes Association's chief scientific officer at the time publicly called implausible [21]. The authors themselves state they cannot infer causation, note that a quarter of participants were lost to follow-up, and caution that the results come from one population [10]. No other cohort has replicated the diabetes finding in the nine years since.

What about blood sugar directly?

This is the one place the evidence is strong enough to say something definite, and what it says is that there is no effect. Four randomized trials gave nitrate or beetroot juice to people with type 2 diabetes and measured glucose outcomes. A two-week crossover in 27 patients found no change in insulin sensitivity by the gold-standard clamp method [12]. An acute crossover in 18 men found no change in glucose or insulin after a glucose tolerance test [13]. A 12-week trial found no change in fasting glucose, insulin or HbA1c after adjusting for baseline [22]. A fourth found no change in plasma glucose [17]. Chlorhexidine itself has been tested against glucose twice, and both studies were null; a six-month Japanese study often cited as showing mouthwash helps diabetes found no overall HbA1c change once seasonal variation was accounted for [23].

The animal research is positive, which is where the enthusiasm comes from. In mice, nitrate reverses a prediabetic state and improves insulin signaling [24]. A 2021 review explains why this has not carried over: rats make their own vitamin C and have plasma levels roughly eight times higher than humans, which drives the stomach's conversion of nitrite to nitric oxide; humans do not, and people with diabetes often have lower vitamin C and less stomach acid still [25].

What this means at your next visit

The strongest finding in this literature for a dental practice has nothing to do with mouthwash. Across five independent datasets from five countries, nitrate-reducing bacteria were lower in people with periodontitis, and in a clinical study of 42 patients, salivary nitrate-reducing capacity was reduced before treatment and returned to healthy levels 90 days after periodontal therapy [14]. Treating gum disease restores the mouth's capacity to do this job. Whether that raises nitric oxide in your blood has not been shown; resting nitrite levels did not change in that study [14].

Chlorhexidine does not need the nitric oxide argument to justify short courses. It is prescription-only, labeled for use between dental visits as part of gingivitis treatment, with reevaluation at least every six months [26]. The Cochrane review of 51 trials found it reduces plaque substantially, but the benefit for mild gum inflammation was too small to be clinically meaningful, and staining becomes common after four weeks: at six months, 56 percent of users had visible front-tooth staining versus 35 percent of controls [27]. The ADA describes mouthrinse as "not a substitute for mechanical oral hygiene," and the European periodontal guideline positions antiseptic rinses as adjuncts [28][29].

So the advice is unchanged, and the nitric oxide story is a supporting reason rather than the foundation. Eat leafy greens and beets. Brush, clean between your teeth, and clean your tongue. If you have gum disease, treat it. If we prescribe chlorhexidine, use it for the course we specify and stop. For an everyday rinse, a fluoride rinse or an alcohol-free rinse does what most people want without broadly suppressing the bacteria that do useful work; the alcohol-based antiseptic formulas are better kept for short stretches, the same way we think about chlorhexidine. If you have high blood pressure and use an antiseptic rinse twice a day indefinitely, it is a reasonable thing to mention to us and to your physician, not something to panic about.

Questions patients ask

Should I stop using mouthwash? If it is a fluoride or alcohol-free rinse, there is no evidence it affects blood pressure or blood sugar. If it is an alcohol-based antiseptic rinse you use every day, consider switching to an alcohol-free one; the alcohol-based formulas reduce bacterial diversity, including nitrate reducers, and dry the mouth. If you were prescribed chlorhexidine, use it for the course specified and then stop; staining and the nitric oxide effect are both reasons not to continue indefinitely.

I have high blood pressure. Does this change anything? The trials that found a blood pressure rise used chlorhexidine for a week or less, and the rise was 2 to 3 mmHg. If you use an antiseptic rinse twice a day long term, mention it to us and to your physician; it is a detail worth knowing, not an emergency.

Will eating more beets lower my blood sugar? No. Four trials in people with type 2 diabetes found no effect on glucose, insulin sensitivity or HbA1c. Nitrate-rich vegetables are still good for you, and they do lower blood pressure modestly, but blood sugar is not where the benefit shows up.

Does tongue scraping help or hurt? Tongue cleaning removes the film where many of these bacteria live, and one study found habitual tongue cleaners responded differently to chlorhexidine. The evidence is too thin to recommend for or against it on nitric oxide grounds; clean your tongue if it helps your breath and comfort.

Can a probiotic restore the "good" bacteria? No oral probiotic has been shown to raise nitrate-reducing capacity in people. The intervention with the best evidence for shifting the oral community toward nitrate reducers is simply eating more nitrate-rich vegetables [15].

The next step

If you have been using an antiseptic rinse daily for months, have gum disease that has not been treated, or have questions about how your mouth fits into your blood pressure or diabetes care, Loul Dental Studio can examine your gums, review what you are using at home, and coordinate with your physician, for patients in Santa Barbara and Montecito. Request an appointment online (a request is not a confirmed appointment; the team follows up) or call (805) 565-5111 during office hours.