Mouthwash may kill coronavirus in a lab but it won't stop transmission among people

• Using mouthwash is not an effective way to prevent the spread of the coronavirus.
• Studies have shown that certain oral rinses are capable of killing the virus in a lab.
• But using mouthwash does not decrease the viral load in your nose and lungs, and therefore will not affect coronavirus transmission.
• The recent study has ties to the company that makes Dentyl mouthwash.

A new study by researchers at Cardiff University found certain mouthwash formulations can kill coronavirus within 30 seconds in a laboratory setting.

The preprint, which has not yet been peer reviewed, echoes similar findings of a study of mouthwashes and nasal rinses published in the Journal of Medical Virology in September.

The practice appears to have been picked up by some film sets. Stars like KJ Apa and Camilla Mendes of "Riverdale" have added a 30-second rinse as an extra precaution before makeout scenes.

However, experts warn that, in reality, mouthwash should not be used in hopes of preventing coronavirus transmission because it does not stop all avenues of viral spread.

"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," Vincent Racaniello, professor of microbiology and immunology at Columbia University, previously wrote in an email to Insider.

Mouthwash may be useful in some settings, such as dental offices, but that's because dentists wear face masks and shields for additional protection and typically have their patients rinse frequently, Racaniello added.

Any virus-killing effects of mouthwash are temporary

Three mouthwash formulations tested in the Cardiff study eliminated all traces of the coronavirus within 30 seconds. But the data represent only a short moment in time without considering other biological processes that affect viral load.

"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, previously told Insider.

"Titer," or viral load, refers to the amount of virus in a given volume of fluid. The most effective mouthwashes in the Cardiff study, which contained either cetylpyridinium chloride or ethyl lauroyl arginate as the active ingredient, reduced the viral load by more than five logs — a strong reduction by industry standards.

In a German study published in the Journal of Infectious Diseases in July, the most powerful mouthwash reduced the load by about three logs, which corresponds with bottle labels that say it "kills 99.9% of germs," Graham said.

But no rinse on the market can inhibit cells from producing new viruses, and the effects of mouthwash will not — and should not — reach your nose or lungs.

The next phase of research is funded by the company that makes Dentyl mouthwash

The team at Cardiff University has already begun assessing the efficacy of mouthwash containing cetylpyridinium chloride in COVID-19 patients.

While the researchers claimed no direct conflicts in the preprint of the lab study, this next stage is funded by Venture Life Group, the company that makes Dentyl mouthwash. Incidentally, Dentyl is one of the few oral rinses that contain cetylpyridinium chloride.

The researchers wrote in the preprint: "Venture Life Group provided information on mouthwash formulations employed in the study, but had no role in funding, planning, execution, analysis, or writing of this study."

Venture Life Group did not respond immediately to a request for comment.