Listerine isn’t dangerous for most people, but using it twice a day or more may come with tradeoffs that go beyond your mouth. The essential oils in Listerine (menthol, eucalyptol, thymol, and methyl salicylate) are genuinely effective at killing bacteria that cause gum disease and plaque. The concern is that they also kill beneficial bacteria your body relies on for functions like blood pressure regulation and blood sugar control. Whether Listerine is “bad for you” depends on how often you use it and what health conditions you’re managing.
The Dental Benefits Are Real
Listerine does what it claims to do for your teeth and gums. In a 12-week clinical trial published in the Journal of Dental Hygiene, people who brushed and rinsed with an essential oil mouthwash saw plaque reduced by about 36% and gingivitis reduced by 51% compared to brushing alone. Gum bleeding dropped by roughly 69%. Those are significant improvements, and they held up even between the teeth, where brushing alone tends to miss.
Interestingly, adding flossing on top of brushing only reduced gingivitis by about 9% compared to brushing alone, while adding Listerine reduced it by over 50%. That doesn’t mean you should skip flossing, but it does explain why dentists sometimes recommend an antiseptic rinse for people who struggle with gum inflammation.
What It Does to Your Oral Microbiome
Your mouth contains hundreds of bacterial species, and many of them are doing useful work. Research published in Frontiers in Cellular and Infection Microbiology found that gargling Listerine significantly reduced bacterial diversity at the genus level. Seven bacterial groups dropped in abundance after rinsing, including species involved in converting nitrate, a process your cardiovascular system depends on (more on that below).
The good news is that Listerine’s impact on the microbiome was smaller than chlorhexidine, the prescription-strength antiseptic rinse dentists use for serious gum infections. The bacteria Listerine targeted were not among the 20 most abundant groups in the mouth, meaning it disrupts the ecosystem less dramatically. Still, daily use over months and years is a different story than a short-term study, and researchers have noted that long-term effects on the oral microbiome remain unclear.
The Blood Pressure Connection
This is where things get more concerning if you have cardiovascular risk factors. Certain bacteria on your tongue perform a specific job: they convert nitrate from your food into nitrite, which your body then uses to produce nitric oxide. Nitric oxide relaxes blood vessels and helps lower blood pressure. It’s one of the most important molecules in cardiovascular health.
Antiseptic mouthwash disrupts this process by killing the bacteria responsible for that conversion. A study published in the European Journal of Pharmacology found that when researchers used antiseptic mouthwash to reduce oral bacteria, it completely eliminated the blood pressure-lowering benefits of L-arginine (an amino acid the body uses to make nitric oxide) in hypertensive subjects. The mouthwash also blocked improvements in endothelial function, which is the ability of blood vessels to dilate properly.
If you’re otherwise healthy with normal blood pressure, this effect is probably minor. But if you’re taking blood pressure medication, exercising to manage hypertension, or eating a nitrate-rich diet (beets, leafy greens) for cardiovascular benefit, an antiseptic rinse twice a day could be working against those efforts.
A Possible Link to Diabetes Risk
A three-year study following more than 900 overweight or obese adults found that people who used mouthwash twice or more daily were 55% more likely to develop prediabetes or diabetes compared to those who used it less frequently. They were 49% more likely to develop these conditions compared to people who didn’t use mouthwash at all.
The proposed explanation ties back to the same nitric oxide pathway. Nitric oxide plays a role in insulin signaling and metabolic regulation, so chronically suppressing the oral bacteria that help produce it could, in theory, nudge metabolic function in the wrong direction. This is a single observational study, not proof of cause and effect. People who use mouthwash more frequently might share other habits or health conditions that raise diabetes risk. But combined with the blood pressure evidence, it adds to a pattern worth paying attention to.
Does the Alcohol Cause Dry Mouth?
Original Listerine contains about 21-27% alcohol, which is a common concern. Many people assume it dries out your mouth, and a dry mouth does raise the risk of cavities and bad breath. But the clinical evidence is less alarming than the reputation suggests.
A study comparing alcohol-based Listerine to an alcohol-free mouthwash over 12 weeks found no significant difference in salivary flow or perceived dryness in people who started with normal saliva production. The researchers noted that despite widespread claims in popular media about alcohol-based rinses drying out the mouth, no published studies had actually confirmed it.
That said, if you already experience dry mouth from medications, aging, or medical conditions like Sjögren’s syndrome, alcohol-based rinses can make the sensation worse. In those cases, alcohol-free versions of Listerine or other rinses are a reasonable alternative. The essential oils, not the alcohol, are responsible for most of the antibacterial effect.
Who Should Be Cautious
Once-a-day use for someone with healthy blood pressure and no metabolic concerns is unlikely to cause meaningful harm, and the gum health benefits may outweigh the microbiome disruption. The risk calculus shifts for a few groups:
- People managing high blood pressure. If you rely on diet, exercise, or medication to control blood pressure, twice-daily antiseptic rinsing may partially counteract those efforts by suppressing nitric oxide production.
- People at risk for type 2 diabetes. The association between frequent mouthwash use and increased diabetes risk is preliminary, but if you’re already overweight or have prediabetes, it’s worth discussing with your dentist whether you need an antiseptic rinse at all.
- Children under six. The American Dental Association recommends against mouthwash use for children under six, primarily due to the swallowing risk.
Alternatives to Consider
If you’re using Listerine mainly for fresh breath, you’re getting more antibacterial effect than you probably need. Brushing thoroughly and cleaning between your teeth handles most of the bacteria responsible for bad breath. A simple saltwater rinse or alcohol-free rinse without antiseptic agents can freshen your mouth without disrupting beneficial bacteria.
If your dentist has recommended Listerine specifically for gingivitis or plaque control, the benefits are well documented and likely worth the tradeoffs for a defined treatment period. The key distinction is between using it as a targeted tool for gum disease and using it as a daily habit out of routine. For people without active gum problems, the most honest answer is that Listerine probably does more than your mouth needs, and that “more” comes with a cost to bacterial communities your body uses for other purposes.