There have been online posts saying mouthwash can disrupt your oral microbiome and lead to serious health issues. Is that true? The claims on social media can be jarring. Regularly using mouthwash, some say, could wipe out the "good" bacteria in your mouth, increasing the risk of developing Type 2 diabetes, high blood pressure, heart disease and even issues with blood flow to the brain. The mouth is host to a delicate balance of microbes, including bacteria that, when thrown out of whack, can have downstream effects on health, some research has found. But can mouthwash really do all that? We asked experts to help us understand the risks.

What the research suggests

Using any over-the-counter mouthwash occasionally, such as once a week or once a month, is unlikely to damage your oral or general health, said Dr Purnima Kumar, a professor of periodontics and oral medicine at the University of Michigan School of Dentistry. But swishing certain types of mouthwash multiple times a day for months and years on end, she said, might have some damaging effects. "Do I have a bottle of mouthwash next to my toothbrush? Absolutely. But do I use it every day? Certainly not," Dr Kumar said.

Mouthwash typically falls into two categories: therapeutic mouthwashes, which contain active ingredients that kill bacteria and help with common dental issues such as bad breath, gum disease and tooth decay; and cosmetic mouthwashes, which temporarily mask bad breath and leave a pleasant taste in your mouth but don't contain germ-killing active ingredients.

The goal with good oral care is to remove the harmful bacteria that cause common dental issues while maintaining the beneficial bacteria that prevent those issues, said Dr Vivek Thumbigere-Math, an associate professor of periodontics at the University of Maryland School of Dentistry. Brushing, flossing and regular dental cleanings help with that goal, he said. But some limited and emerging research has found that certain types of mouthwash — especially therapeutic mouthwash containing the antiseptic chlorhexidine, which is only available via prescription in the United States — may alter the oral microbiome and some of its normal functions.

In one small trial published in 2020, for instance, 36 healthy adults in Britain rinsed their mouths twice a day for seven days with a placebo mouthwash, and then did the same with a mouthwash containing chlorhexidine. The chlorhexidine mouthwash was associated with "a major shift in the salivary microbiome," the researchers reported, as well as a more acidic mouth (which can increase the risk of cavities) and fewer bacteria that are linked with healthy blood pressure.

It's unclear whether other antiseptic ingredients found in popular over-the-counter mouthwashes — like cetylpyridinium chloride, essential oils, iodine or hydrogen peroxide, which are contained in some Colgate, Crest and Listerine products — may alter the microbiome as much as chlorhexidine. Logic and some limited research suggests they might if used long-term, said Dr Richard Nejat, a periodontist in New York City, so it's best to avoid using them for long periods unless you need to treat a specific dental issue.

Growing evidence suggests that disruptions to the oral microbiome can affect cardiovascular health. Oral bacteria convert nitrates from food into nitric oxide, which relaxes blood vessels and lowers blood pressure, Dr Kumar said. Some research has also found links between using mouthwash regularly (such as twice a day for years) and elevated risks of developing Type 2 diabetes and high blood pressure. However those studies had many limitations and have not proved cause and effect, Dr Thumbigere-Math said.

Alcohol- or peroxide-based rinses can also irritate the gums, tongue, inner cheeks and other soft tissues, the experts said. And ingredients like essential oils or foaming agents can cause burning, ulcers or in some extreme scenarios, peeling inside the mouth.

Choosing the right mouthwash

If you do need to use mouthwash, such as if a dental professional recommends or prescribes one, it's best to opt for one that addresses a focused issue, rather than a product that treats a wide range of issues with multiple active ingredients, Dr Thumbigere-Math said.

If you're at high risk for cavities, for instance, you may benefit from a fluoride-containing mouthwash, Dr Thumbigere-Math said. Or if you have dry mouth, he said, it might help to use a rinse with ingredients designed to stimulate or mimic saliva. Patients who temporarily can't brush or floss as usual, including after certain dental procedures, may also benefit from using therapeutic mouthwashes, Dr Nejat said.

Fluoride mouthwashes can be safer long-term than antiseptic mouthwashes, Dr Nejat said, because they work mainly by strengthening enamel rather than killing bacteria. Those with dry mouth, sores in the mouth or sensitive gums or teeth should opt for alcohol-free washes, Dr Nejat said; and Dr Thumbigere-Math said that those with sensitive teeth should avoid frequent use of whitening rinses.

Mouthwash is optional for most people, he said; there's no substitution for brushing, flossing and regular professional cleanings. "Mouthwash is not a lifelong, everyday kind of a thing," Dr Kumar added, especially if it's prescription-based.

So, is mouthwash bad for you?

For most people, occasional use of over-the-counter mouthwash is unlikely to cause harm. The concern is mainly around long-term, frequent use of antiseptic mouthwashes, which may disrupt the oral microbiome and potentially affect blood pressure and metabolic health. If you need mouthwash for a specific issue, choose a targeted product and use it as directed. Otherwise, stick to brushing, flossing and regular dental check-ups — and keep mouthwash as an occasional extra rather than a daily habit.