The key to good oral hygiene for reducing dental plaque, gingivitis, tooth decay—and bad breath—is tooth brushing, using dental floss (or a water pick or an interdental brush) to remove food debris from between your teeth, and seeing your dentist regularly. But what about mouthwash? Drugstore shelves are crowded with these products that make big promises. Are they worth adding to your oral arsenal?
Bad breath is caused by bacteria in the mouth that produce volatile and odiferous sulfur compounds. Food that gets stuck between teeth, on your gums, or on your tongue is a breeding ground for these bacteria. Odor-producing bacteria are also present in dental plaque, which builds up, especially if you don’t follow good oral hygiene practices.
Using a mouthwash that contains antimicrobial agents—essential oils (for example, menthol, thymol, and eucalyptol as found in Listerine), cetylpyridinium, or chlorhexidine—can help control bad breath by reducing the bacteria. (The latter two ingredients can both cause tooth staining with regular use, however; chlorhexidine is available by prescription only.) These antimicrobial ingredients can also, along with tooth brushing and flossing, help control dental plaque and gingivitis by disrupting the cellular structure of bacteria—that is, killing the bacteria—and inhibiting oral bacterial enzymes, thereby preventing adhesion of bacteria to the surface of teeth.
An ingredient toss-up?
Because studies on mouthwash have had varying methodologies and many have not been well controlled—plus, people use mouthwash for different reasons—it’s hard to single out one ingredient that is better than another. But a 2018 review paper of 26 studies found that using a mouthwash with essential oils (Listerine) twice a day for three to six months along with brushing teeth and flossing was at least as good at controlling plaque and gingivitis as mouthwashes containing chlorhexidine or cetylpyridinium, or simply brushing and flossing.
Meanwhile, a 2017 review by the Cochrane Collaboration, which included dozens of randomized controlled trials, found that swishing with a chlorhexidine mouthwash was associated with a reduction in mild gum disease after at least a month of use, but it wasn’t clear whether it was effective for people with moderate to severe gum disease. If you already have plaque buildup or gum disease, a mouthwash won’t help.
Regarding bad breath, an older review of 12 studies in the International Journal of Dental Hygiene found that nearly all mouthwashes reduced oral odors in both the short-term and longer-term trials, with the best evidence for chlorhexidine mouthwashes and those that contained a combination of cetylpyridinum chloride and zinc. A 2021 study in the Journal of Clinical Medicine also provided some evidence that a zinc-containing mouthwash—in combination with brushing and tongue scraping—was effective at inhibiting the odiferous sulfur compounds that cause bad breath.
According to the American Dental Association, there are a variety of dental conditions for which certain kinds of mouthwashes can be effective, including using a chlorhexidine mouthwash to reduce the risk of dry socket (aka alveolar osteitis), a painful dental condition that occurs after a tooth extraction. If you have dry mouth (xerostomia), using a mouthwash like Biotene that contains lubricants (propylene glycol) and humectants (such as glycerin) can help the oral tissues retain water and moisturize the mouth.
Mouthwash modus
Directions may vary depending on the ingredients or manufacturer, but in general you want to use a small amount of mouthwash (about three to five teaspoons) and swish it around your mouth vigorously for 30 seconds before spitting it out. Typically, the bottles come with caps that can be used as a measuring tool.
For best results, you should use mouthwash after you brush and floss—but, importantly, be sure to wait about five minutes after brushing; otherwise, the mouthwash could rinse away the cavity-fighting fluoride in the toothpaste. You can also use a mouthwash at a different time of the day than when you brush as a quick freshener. Needless to say, mouthwashes should not be swallowed.
Lasting effects?
There’s little research addressing how long the breath-freshening effects of mouthwash last, especially because it depends on so many factors, including your overall oral hygiene, whether you have dental conditions such as periodontal disease, and how often you use mouthwash. One small study determined that the effects of a mouthwash containing zinc acetate and chlorhexidine lasted 12 hours.
The alcohol conundrum
Alcohol is used as a preservative and flavoring agent in mouthwash and for its ability to help dissolve other ingredients. But its presence has been controversial because of concerns that acetaldehyde, a metabolite of alcohol, may cause mutations in the mouth and play a role in oral cancers.
But there’s no clear evidence that alcohol-based mouthwashes actually cause cancer; studies have been inconsistent. A 2020 systematic review of eight studies, for instance, found a relationship between alcohol mouthwashes and oral cancer in three of the studies evaluated but no relationship in another three studies; two other studies found temporary increases in saliva acetaldehyde levels. The authors noted that any increased risk may be related to other risk factors associated with cancer, such as drinking alcohol and smoking.
Alcohol also has a drying effect in the mouth, which is counterproductive to combating bacteria and bad breath, since saliva is naturally protective. And it can burn gums. Nowadays, however, you can find plenty of mouthwashes that don’t contain alcohol.
BOTTOM LINE: If you’re thinking of adding a mouthwash to your oral hygiene, talk with your dentist about which one might be best for you, especially if you have dry mouth, bleeding gums, or oral lesions. If you have bad breath on a regular basis, be aware that mouthwash is only a temporary solution at best. Your dentist can help explore whether the problem is due to an oral hygiene issue or another health condition, such as acid reflux.
There is increasing interest in the body’s microbiome and its effect on health. In addition to the gut microbiome (the population of microorganisms, including bacteria, in the gastrointestinal tract), there are microorganisms in the mouth (the oral microbiome) that can affect health beyond teeth and gums. And some recent research suggests that mouthwash may interfere with this delicate balance of oral bacteria.
- A small study in Frontiers in Cellular and Infection Microbiology in 2019 looked at bacteria in the mouth that are important for cardiovascular health because they can convert nitrate found in foods to nitrite and nitric oxide, which help maintain normal blood pressure. The investigators found that using mouthwash with chlorhexidine twice a day for a week changed the oral bacterial population and was associated with an increase in systolic (the top number) blood pressure.
- Another study, in Scientific Reports in 2020, similarly found that using a chlorhexidine-containing mouthwash for a week changed the oral bacterial population such that there was an increase in certain types of bacteria and a reduction in other types; overall, there was a decrease in the diversity of the bacterial population, as well as a drop in the pH of the saliva (meaning it became more acidic). Longer-term studies are needed to know what the health consequences of these changes might be, but a more acidic oral pH could increase the risk of cavities and even tooth loss and may be linked with chronic periodontal disease.
- A study in Nitric Oxide in 2017 included a large number of overweight or obese middle-aged and older people without cardiovascular disease or diabetes who were asked about their use of mouthwash (how often) and followed for three years. Those who used mouthwash at least twice a day (but not less often) had an increased risk of prediabetes or diabetes, even after controlling for other risk factors like fasting blood sugar levels and diet. Again, nitric oxide might be involved: It’s hypothesized that mouthwashes with antibacterial ingredients could knock out bacteria involved in the formation of this compound, which helps regulate insulin and therefore blood sugar levels.
The idea that mouthwash may adversely impact your health through its effects on the oral microbiome is intriguing—but unproven as yet. Still, such preliminary findings serve as a reminder that most practices are best done in moderation. If you use mouthwash, don’t go overboard—a once-daily swish should generally suffice.
