Is Mouthwash Bad for You? Bacteria, Blood Pressure, Cancer

Mouthwash is not bad for you in the way some headlines suggest, but it is not harmless either. Fluoride rinses help prevent cavities, and antimicrobial rinses reduce plaque^[1][2]. The concern is that strong antiseptic rinses also kill helpful mouth bacteria, and in small trials that nudged blood pressure up by a few points^[3].

Below: what happens to good bacteria, blood pressure, diabetes risk and cancer risk. It also covers alcohol versus alcohol-free rinses, daily use, and who actually benefits from rinsing.

What does mouthwash actually do?

It depends on the type. The American Dental Association (ADA) splits rinses into two groups^[4]:

• Cosmetic rinses mask bad breath and leave a pleasant taste, but have no effect on bacteria or the sulfur gases behind odor.
• Therapeutic rinses contain an active ingredient meant to control plaque, gingivitis, bad breath or tooth decay.

The active ingredient decides both the benefit and the downside.

Does mouthwash kill good bacteria?

Yes. Antiseptic rinses are not selective, so they reduce helpful species along with harmful ones. A 2023 review in the International Dental Journal concluded that chlorhexidine and similar rinses may cause "dysbiosis": some species are killed and others, sometimes unwanted ones, take over^[8].

Here is what that looked like in two groups of volunteers:

• Chlorhexidine for 7 days. In 36 healthy adults, twice-daily rinsing increased Firmicutes and Proteobacteria and reduced Bacteroidetes and Fusobacteria. Saliva became more acidic, with less buffering capacity and more lactate and glucose^[9].
• Listerine Cool Mint for 3 months. In 59 men in a randomized crossover trial, daily use raised levels of Fusobacterium nucleatum and Streptococcus anginosus in the throat. Both are opportunistic bacteria linked to gum disease^[5].

The same review notes emerging evidence of antimicrobial resistance with mouthwash use, and says it is still uncertain which rinse best "balances" the oral microbiome^[8]. Helpful residents such as Streptococcus salivarius and Streptococcus oralis live alongside the species a rinse is meant to suppress.

Why do cardiologists warn against mouthwash?

Because some mouth bacteria help your body make nitric oxide, which relaxes blood vessels. The pathway works like this^[3]:

1. Nitrate from vegetables and from your own metabolism is pulled from the blood into saliva.
2. Mouth bacteria convert nitrate to nitrite.
3. Swallowed nitrite enters the blood, where it can form nitric oxide.

Strong antiseptic rinses break step 2. In a study of 19 healthy volunteers, a week of chlorhexidine cut oral nitrite production by 90% and plasma nitrite by 25%. Systolic and diastolic blood pressure rose by 2 to 3.5 mmHg, starting within one day^[3].

The effect also appeared in people already treated for hypertension. In a randomized crossover trial of 15 adults with a mean age of 65, three days of antibacterial mouthwash raised systolic pressure by 2.3 mmHg compared with water^[10]. In rats, antiseptic mouthwash wiped out the blood-pressure-lowering effect of dietary nitrate^[11].

Not all rinses act the same. In 12 healthy men given beet juice, chlorhexidine and a CPC rinse lowered saliva and blood nitrite more than an essential-oil antiseptic or water^[12].

What the long-term studies show

The San Juan Overweight Adults Longitudinal Study followed overweight and obese adults aged 40 to 65 for three years^[13]:

• High blood pressure. Among 540 people without hypertension at the start, those who used mouthwash twice a day or more were 85% more likely to be diagnosed with it than less frequent users (incidence rate ratio 1.85)^[14].
• Prediabetes and diabetes. Among 945 people, twice-daily users had a 55% higher rate of developing prediabetes or diabetes. Use less than twice a day showed no link, which suggests a threshold^[13]. See our page on type 2 diabetes and the microbiome.
• Nitrite. Twice-daily users also had lower blood nitrite levels^[15].

How strong is the evidence?

Moderate for the mechanism, weak for long-term harm. The blood pressure trials were small (12 to 36 people), short (3 to 7 days) and mostly used chlorhexidine, a prescription-strength agent^[3][10][9]. The long-term data come from one cohort of overweight and obese adults, so they show an association, not cause and effect. In that study, blood pressure measured at a single visit showed no link^[14].

The practical reading: a few millimeters of mercury matters most if your blood pressure is already high. Do not stop or change blood pressure medication based on this; raise it with your doctor or dentist instead.

Does mouthwash cause cancer?

The best evidence says no clear link. A meta-analysis of 18 studies found no significant association between regular mouthwash use and oral cancer (relative risk 1.13, 95% CI 0.95 to 1.35), and no trend with more daily use of alcohol-containing rinses^[16]. A 2020 review focused on alcohol rinses reached the same conclusion: there is not enough evidence that they influence oral cancer^[17]. The ADA cites this finding too^[4].

One caveat: a 2021 meta-analysis of 17 studies (17,085 cases) found no overall link but a small, statistically significant increase in head and neck cancer with frequent use^[18]. The authors suggested prolonged contact with ingredients such as alcohol as a possible reason.

Is alcohol mouthwash worse than alcohol-free?

For comfort, usually yes; for effect, slightly better. Alcohol is drying, so the ADA suggests an alcohol-free fluoride rinse for people with dry mouth^[4]. It can also cause intoxication if young children swallow it^[4].

A 2024 meta-analysis of essential-oil rinses found that alcohol-free versions controlled plaque slightly less well. There was no clear difference for gum bleeding or inflammation, and people preferred the taste of the alcohol-free rinses^[19].

Going alcohol-free does not solve the bacteria question. CPC, a common alcohol-free active, lowered nitrite about as much as chlorhexidine in one small trial^[12].

Is it bad to use mouthwash every day?

Not for most people, but daily use only makes sense if you have a reason. In the long-term cohort, the links with high blood pressure and diabetes appeared at twice a day or more, not with less frequent use^[13][14].

The authors of a 2023 practice review concluded that mouthwash may add little for people with healthy gums and a low cavity risk. Their reasons were allergy risk, disruption of mouth bacteria, antimicrobial resistance and environmental harm^[20]. Prescription chlorhexidine is meant for short courses: four weeks or more causes tooth staining^[7].

Who benefits from mouthwash, and who can skip it?

Mouthwash is an add-on, not a substitute. The ADA and a 2023 practice review both frame it as an extra on top of brushing and cleaning between the teeth^[4][20].

If you have bleeding gums, see our guide to periodontal disease. If bad breath is the reason you rinse, a cosmetic rinse only masks it; our halitosis guide covers the causes.

How to use mouthwash with less downside

1. Rinse for a reason. Match the active ingredient to the problem, using the table above.
2. Use fluoride rinses at a different time from brushing, such as after lunch, so you keep the toothpaste fluoride on your teeth^[21].
3. Keep antiseptics to the label dose. The diabetes and blood pressure associations appeared at twice a day or more^[13].
4. Treat chlorhexidine as a short course. Use it only as prescribed; staining builds after four weeks^[7].
5. Look for the ADA Seal of Acceptance, which means the maker provided data for its claims^[4].
6. Freshen breath without an antiseptic where you can. Our tongue scraping guide covers the evidence.

If you take blood pressure medication and use a strong antiseptic rinse daily, mention it at your next appointment. Your clinician can weigh the oral benefit against the small blood pressure effect.

This article is for general educational purposes and is not medical or dental advice. The evidence on mouthwash and blood pressure comes mainly from small, short trials and one observational cohort. Talk to your dentist or doctor before starting or stopping a prescribed rinse or changing any medication, particularly if you are pregnant, immunocompromised, taking prescription medication, or managing high blood pressure or diabetes.