Mouthwash

For healthy gums, you don't need a daily mouthwash: brushing and cleaning between the teeth do the work. Use chlorhexidine only as a short course (1–2 weeks) when a dentist prescribes it, for example after surgery or an extraction.

What it does to your tongue bacteria

Leafy greens and beetroot contain nitrate. Your salivary glands concentrate it and pour it back into the mouth, where bacteria on the back of the tongue (Neisseria, Rothia, Haemophilus and others) turn it into nitrite. Swallowed nitrite becomes nitric oxide, which relaxes blood vessels. This route runs alongside the body's own nitric-oxide-making enzymes, which become less efficient with age.^[1]

Chlorhexidine, a strong antiseptic, shuts this route down. In 19 healthy volunteers, a week of rinsing twice a day cut the mouth's nitrite production by 90% and blood nitrite by 25%, and blood pressure rose by 2–3.5 mmHg, tracking the fall in nitrite.^[2] In a one-week trial in 45 healthy adults, chlorhexidine again impaired the mouth's nitrite-producing activity, while a propolis rinse caused no significant change.^[3]

The blood-pressure question is still open

The nitrite drop is robust; the blood-pressure harm is plausible but unproven. Two separate meta-analyses, each pooling five studies, found no significant rise. One, of controlled crossover trials of mouth rinses, put systolic pressure 1.59 mmHg higher, with a 95% confidence interval (the range where the true effect most plausibly lies) from -0.15 to +3.33 mmHg.^[4] The other, of chlorhexidine specifically, found 1.56 mmHg higher, with an interval from -0.67 to +3.80 mmHg, and judged any rise clinically negligible.^[5] Both intervals include zero. A small 2026 randomised trial in 90 people who rinsed with chlorhexidine, octenidine or salt water for 21 days also found no clinically meaningful change.^[6]

One observational study points the other way. Among 540 overweight adults, using ordinary over-the-counter mouthwash twice a day or more went with more new cases of high blood pressure over three years.^[7] That is an association, not a trial, and it covers everyday antiseptic rinses rather than chlorhexidine.

Gentler rinses are not automatically safe

Whether a rinse spares the nitrate-reducing bacteria depends on the ingredient, and the studies are small and short:

• In 12 people, an essential-oil rinse had little effect on a key nitrate-reducing tongue bacterium.^[8]
• In 12 healthy men, Listerine (also an essential-oil rinse) behaved like water, while an antibacterial rinse, Cepacol, lowered saliva and blood nitrite much as chlorhexidine did.^[9]
• In 12 volunteers drinking beetroot juice for six days, even a weak non-chlorhexidine rinse blunted the rise in blood nitrite.^[10]

No rinse has been shown to be free of long-term effects.

Where chlorhexidine still belongs

Chlorhexidine and high-alcohol mouthwashes were designed for short-term use after surgery, not as daily hygiene products. Chlorhexidine has real costs (staining, taste disturbance, microbiome disruption, and saliva that loses some of its buffering capacity) and no demonstrated benefit for a healthy mouth. It remains appropriate as a short-term (1–2 week) rinse after mouth surgery or an extraction, on a dentist's instruction.

It hasn't been shown to help Alzheimer's disease either. A small 24-week trial in 66 people with mild Alzheimer's found that wiping the mouth with chlorhexidine shifted their gum bacteria but did not significantly improve cognition scores; its main outcome was the bacteria, not cognition, and it compared against usual care, with no placebo or blinding.^[11] See Porphyromonas gingivalis for the wider story.

What to do

1. With healthy gums, skip daily mouthwash. Brush twice a day with fluoride toothpaste and clean between your teeth.
2. Don't use chlorhexidine or another antibacterial rinse every day unless a dentist prescribed it for a specific short-term reason.
3. If you use a rinse anyway, small short studies found an essential-oil rinse gentler on these bacteria than antibacterial ones, but no rinse has been shown to be free of long-term effects.
4. Eat leafy greens or beetroot regularly; they feed the bacteria a harsh mouthwash kills. See Oral health.

Further reading

• Kapil V et al. Physiological role for nitrate-reducing oral bacteria in blood pressure control. Free Radic Biol Med 2013.^[12]
• Toonen LSJ et al. The Effect of Chlorhexidine Mouthwash on Blood Pressure: A Systematic Review and Meta-Analysis. Int J Dent Hyg 2026.^[13]
• Joshipura K et al. Over-the-counter mouthwash use, nitric oxide and hypertension risk. Blood Press 2020.^[14]