Antibacterial Mouthwash: Oral Microbiome and Blood Pressure

Nitric oxide (NO) is a molecule that widens blood vessels and so helps keep blood pressure normal. The body produces it in two ways: enzymatically in endothelial cells, and through the nitrate–nitrite–NO pathway, whose source is nitrate from food (especially from leafy vegetables and beetroot) and nitrate produced within the body itself.

The key step of this pathway takes place in the mouth. Nitrate circulating in the blood is taken up by the salivary glands and concentrated in saliva. There, certain oral bacteria reduce nitrate to nitrite — and this, once swallowed and absorbed, can be converted to NO. Without these bacteria the first step is blocked. In practice this part of the pathway therefore depends to a large extent on the oral microbiome.

Hence the hypothesis: antibacterial mouthwashes, which by design kill bacteria in the mouth, may incidentally reduce the number or activity of nitrate-reducing bacteria, and thereby lower NO availability and raise blood pressure. This reasoning is biologically plausible, but — as always — we have to check whether it holds in people and what its scale is.

This study is important because it shows the whole causal chain in a single experiment: mouthwash → less nitrite in saliva and plasma → higher blood pressure. It has limitations, however. There were 19 participants, all healthy, the observation period was short (a week), and the 'control first, then mouthwash' design (no random order and no placebo group) does not rule out the influence of accompanying factors, such as changes in habits over two weeks. It is an experiment showing the mechanism and direction of the effect, not proof of long-term harm.

The size of the effect — a few mmHg — is small at the level of a single measurement, which usually fluctuates by a similar amount from minute to minute. At the population level even a small, lasting rise in blood pressure can matter, but that inference requires evidence that the effect persists, which these short studies do not settle.

For people who already have hypertension the question is more practical. A randomised crossover trial in 15 treated people with hypertension (mean age 65) compared 3 days of using an antibacterial mouthwash with water as the control. The mouthwash reduced the oral reduction of nitrate to nitrite, lowered salivary nitrite and raised systolic blood pressure by an average of 2.3 mmHg (95% CI 0.5–4.0; p = 0.01), whereas diastolic pressure and cGMP (a marker of NO action) did not change significantly.

Again: the group was small (15 people), the period very short (3 days), and the change in systolic pressure modest. The result is consistent, however, with the experiment in healthy volunteers and with the mechanism, so it does not look like chance. It is hard to say, though, whether in a person treated with medication who has rinsed daily for years the difference would be visible in check-up measurements and whether it would have clinical significance.

Experimental studies are short, so the question is what happens with years of use. A partial answer comes from a prospective cohort study from Puerto Rico (SOALS) in people aged 40–65 who were overweight or obese. The analysis included 540 people without hypertension at baseline; over 3 years hypertension developed in 12% (66 people). People who rinsed with an over-the-counter mouthwash twice a day or more had a higher incidence of hypertension than those using it less often (incidence rate ratio IRR 1.85; 95% CI 1.17–2.94) and than non-users (IRR 2.17; 95% CI 1.27–3.71) — after accounting for, among other things, age, sex, smoking, physical activity, waist circumference, alcohol and baseline blood pressure. Blood pressure measurements taken at a single visit showed no association.

It is also worth remembering the specifics of the population: they were adults who were overweight or obese, so the results need not apply to lean, healthy people. The authors stressed that the association persisted among never-smokers and that additional potential confounders did not change the result, but it is still only one cohort.

A 2020 systematic review covering 5 human crossover studies and 3 animal studies found that in all the human studies the antibacterial mouthwash had an adverse effect on at least one of the measured parameters: in 5 of 5 studies it reduced salivary nitrite, in 3 of 5 plasma nitrite, and in 4 of 5 it raised blood pressure. The authors noted that effects differed depending on the strength and composition of the mouthwash.

A newer scoping review from 2026 covered 9 studies (4 randomised crossover, 3 non-randomised crossover, 1 active-controlled and 1 observational) of good rated quality. Five of them showed a significant rise in blood pressure after mouthwash and four found no association. The authors judged the pooled evidence inconclusive because of differences in intervention length, mouthwash composition, participant characteristics and measurement schedules, as well as methodological weaknesses in some papers (for example washout periods that were too short, lack of randomisation), and stated that no firm conclusions can be drawn at present.

The conclusion of the Cochrane review: chlorhexidine clearly reduces the amount of plaque, but the improvement in the gums of people with mild inflammation was small, and the price is staining and other adverse effects with longer use. That is why chlorhexidine mouthwashes are usually recommended for a limited time and for dental indications, not for daily, multi-year use. A 2014 meta-analysis (4 six-month studies) showed that an essential-oil mouthwash controlled plaque and gum inflammation better than a control solution, but we do not have separate, unambiguous data on blood pressure for such mouthwashes.

It does not follow that rinsing the mouth is 'bad'. It follows that an antibacterial mouthwash is a supplementary tool with a particular profile of benefits and costs. The foundation of hygiene is mechanical removal of plaque — brushing and cleaning between the teeth (we compare the tools in our article on the water flosser and floss). A mouthwash does not replace these actions.

Incidentally: in a small 2025 study (45 healthy people, 7 days, twice a day), a propolis mouthwash, unlike chlorhexidine, did not disturb nitrite production, and systolic pressure was 2 mmHg lower than at baseline. The authors noted that this change was not associated with a change in the oral microbiome. This is a preliminary observation, without a placebo group, so it is not a basis for recommending propolis — it shows rather that different mouthwashes may act differently.

The state of the mouth and of the cardiovascular system are linked at many levels — we write about the ageing of the oral microbiome and its significance in our knowledge base. That is why the best strategy is to look after your gums while not causing unnecessary disruption to the microbiome.

The evidence does not allow us to claim that mouthwash 'causes hypertension'. It does allow us to say that strong antibacterial mouthwashes affect a pathway involved in regulating blood pressure, and that in several short studies blood pressure rose by a few mmHg. The sensible practical conclusions are simple: do not treat a mouthwash as a daily obligation, use it for a reason and for a limited time, and base your hygiene on the toothbrush and cleaning between the teeth.

People with hypertension who rinse daily with an antiseptic need not panic — they can simply check with the dentist whether the mouthwash is needed and watch their blood pressure at home. It is an example of a topic where humility in the face of uncertainty and small, reversible changes are better than radical decisions.