- Using mouthwash is not an effective way to prevent the spread of the coronavirus.
- Some antiseptic rinses can kill 99% of germs in your mouth, but they do nothing about the viral particles in your nose and lungs.
- The effectiveness of mouthwash also depends on how long you swish it.
- Visit Insider's homepage for more stories.
Mouthwash can help with some aspects of oral health — getting rid of bad breath, preserving healthy gums, and preventing cavities — but blocking coronavirus transmission via makeout is not one of them.
"Riverdale" star KJ Apa posted a video to Instagram Wednesday in which he and costar Camilla Mendes rinsed their mouths with what appeared to be mouthwash before filming a makeout scene. Apa called it "the new normal," implying that the pre-kiss rinse was a new measure to prevent the spread of the coronavirus on set.
Virology expert Vincent Racaniello put to rest any hopes that this could work.
"It's absurd to think that rinsing with mouthwash will make 'making out' safe," Racaniello, professor of microbiology and immunology at Columbia University, wrote in an email to Insider. "Mouthwash will not eliminate virus shed from the nose, for example, and will not eliminate all virus in saliva either — it will be rapidly replenished from infected cells."
Mouthwash can be a helpful precaution in some settings, Racaniello added, such as dental offices. But that's because dentists also wear personal protective equipment and don't get quite so up-close-and-personal with their patients.
Mouthwash might reduce the viral load in your mouth for a moment in time
Certain formulations of mouthwash are effective at reducing the viral load in saliva, according to a German study published in the Journal of Infectious Diseases in July. However, there is no rinse on the market that can inhibit cells from producing new viruses.
"If you're infected and shedding virus from your lungs, you're going to breathe humidified air into your mouth immediately and you're going to be producing saliva immediately, so you will replenish those titers pretty quickly," Rachel Graham, assistant professor of epidemiology at the University of North Carolina at Chapel Hill, told Insider.
"Titer" means the same thing as viral load — the amount of virus in a given volume of fluid. Graham, who is not affiliated with the German study, said some brands of mouthwash did better than others at reducing the viral titer.
The German equivalent of Listerine, for one, reduced the load by about three logs, which corresponds with the "kills 99.9% of germs" you'd see on the bottle, Graham said. But other rinses had less than one log reductions, which would not be enough to reduce the risk of virus transmission even for a moment.
How long you rinse your mouth matters
To reap the full benefits of mouthwash, you have to use it properly. For Listerine, the recommended swish time is 30 seconds twice daily.
Apa and Mendes swilled the liquid for a full minute in the Instagram video, so they passed the test by that measure.
But Graham reiterated that even if the stars diminished the viral titer of their saliva enough to reduce the risk of sharing the virus by spit for a moment, there are still plenty of other avenues of transmission, like the nose and lungs.
"Again, it does nothing to any virus in your nose, and nothing to virus that's in your lungs," Graham said. "I'm assuming that even TV kissing has got some pretty close-up breathing involved."
