Why doctors aren't recommending loading up on Listerine just yet.

By Korin Miller
November 18, 2020
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Back in June, interest started swirling around mouthwash and its potential effects on SARS-CoV-2, the virus that causes COVID-19. The information then came from a meta-analysis published in the journal Function, which posed a theory: Based on mouthwash's ability to disrupt or damage the outer layer of other enveloped viruses, or viruses that have a lipid membrane, that mouthwash could have a similar effect on SARS-CoV-2—possibly helping to reduce transmission.

Now, mouthwash is back in the news with a new pre-print (and thus, not yet peer-reviewed) study published on the BioRxiv server, analyzing the effect of common mouthwashes on SARS-CoV-2 in laboratory settings. And this time, researchers from Cardiff University in the UK have some evidence that mouthwash—three common mouthwashes, to be exact—can kill the coronavirus in as little as 30 seconds.

But here's the thing: This research, thought it sounds promising, doesn't mean a whole lot right now in terms of stopping the spread of COVID-19, and doctors definitely aren't jumping on the bandwagon to start prescribing a daily rinse to lessen your chances of catching or transmitting the virus. Here's everything you need to know about mouthwash and coronavirus—and why you shouldn't start stocking up on Listerine.

Can mouthwash kill the coronavirus?

Technically, yes—some types of mouthwash with certain active ingredients have been shown to inactivate SARS-CoV-2 in vitro, or outside of its normal biological context (aka, in a laboratory setting), albeit one that mimicked the conditions of the naso/oropharynx, or back of the throat. The researchers specifically tested seven different mouthwashes—Corsodyl, Dentyl Dual Action, Dentyl Fresh Protect, Listerine Cool Mint, Listerine Advanced Gum Treatment, SCD Max, and Videne—which "demonstrated a wide spectrum of inactivation ability," meaning some were hits and some were misses.

According to study authors, the two Dentyl products containing cetylpyridinium chloride (CPC), and the Listerine Advanced mouthwash containing ethyl lauroyl arginate (LAE) "eradicated the virus completely after a 30-second treatment." Other mouthwashes, like Videne containing iodinated povidone, SCD Max, and Listerine Cool Mint containing a mix of ethanol and essential oils had just a moderate effect on the virus. But mouthwashes containing ethanol alone, or chlorhexidine (like Corsodyl) didn't have an effect on the virus.

The information gathered from this study suggests that it could be beneficial to test the three mouthwashes effective in killing the coronavirus in vitro in an in vivo (or in a biologically accurate, possibly human) setting against a live virus load. This way, scientists can determine any potential effects of mouthwash on "reducing the risk of virus exposure within the clinical setting."

Does that mean mouthwash can protect you from COVID-19?

As of right now, no; no one is claiming that what has happened in a lab setting can actually translate to real life—that's why the study authors suggested in vivo testing. The World Health Organization (WHO) specifically has this to say on the topic: "Some brands of mouthwash can eliminate certain microbes for a few minutes in the saliva in your mouth. However, this does not mean they protect you from infection." And even Listerine—one of the mouthwashes tested (and deemed effective) in the new study—says on its website that "Listerine mouthwash has not been tested against any strains of coronavirus."

Experts aren't really impressed with the mouthwash-COVID link just yet, either. "It's interesting but this hasn't been studied in real life," William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Health.

"Mouthwash can kill lots of things," adds Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security. "It doesn't translate into preventing infection." In fact, Dr. Adalja tells Health that it's not terribly hard to kill SARS-CoV-2, on a basic level. "[It's] not a hearty virus," he says, and there are "many substances that can deactivate it."

Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo in New York, tells Health that he's "kind of lukewarm" about the findings. "They're just inactivating RNA in a lab setting as opposed to a real-life setting," he says. "But, if you're already infected, that horse has left the barn." What he means here is that, once the virus is actually inside the human body, the damage is already underway, by way of replicating in the upper respiratory tract (the nose, sinuses, throat, bronchial tubes, and lungs).

It's also unclear whether this could be used to prevent infection, Dr. Russo says. "The virus can get into your eyes and nasal cavity, too. Once it gets into your cells, would mouthwash really work?" he says. "That remains uncertain."

On the most basic level, Dr. Adalja cautions about people getting too excited about this. "It's not like you can use the mouthwash, make out with someone, and the risk of contracting COVID-19 is zero," he says.

Do we know how mouthwash could be used in the fight against COVID-19?

That's where this gets especially tricky. "How would you even operationalize this? I don't know that there's a way," Dr. Adalja says. Meaning, you're probably not going to spend your entire day gargling mouthwash—and you shouldn't, he says. "It's also not clear if this would actually decrease infection," Dr. Adalja says.

But Dr. Russo says there's enough evidence to suggest mouthwash could do…something. And, he says, that it's at least worth pursuing. "It would need to be studied in controlled, blinded studies to see if, say, people who regularly use mouthwash are less likely to get infected," he says. Dr. Schaffner agrees. "It probably couldn't hurt," he says.

Overall, experts stress that you shouldn't run out and load up on mouthwash. "These [findings] are all very preliminary," Dr. Russo says.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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