Listerine Antiseptic currently only claims to kill germs that cause bad breath, but researchers have recently found the mouthwash is highly effective at “inactivating” human coronavirus.

In a recent test, even at the lowest contact time of 30 seconds, the mouthwash inactivated greater than 99.99% of human coronavirus in solution.

Because the mouthwash and hydrogen peroxide oral rinses in the study are widely available and easy to use, "I would recommend the use of the rinses on top of wearing mask and social distancing. This could add a layer of protection for yourself and others," lead study author Craig Meyers, PhD, professor of microbiology and immunology and obstetrics and gynecology, Penn State College of Medicine in Hershey, Pennsylvania, told Medscape Medical News.

Meyers and colleagues found that efficacy aligned with duration of time the cell cultures were exposed to each mouthwash or rinse product. Although it varied, the products required at least 30 seconds to kill most of the virus. Waiting 1 or 2 minutes tended to fortify results.

"This study adds to and further confirms the recently published evidence from virologists in Germany that mouthwashes can inactivate the virus that causes COVID-19 in a test tube," Valerie O'Donnell, PhD, co-director of the Systems Immunity Research Institute of Cardiff University, Cardiff, Wales, said when asked to comment on the study.

"While this is great to see, what is still lacking is in vivo (performed or taking place in a living organism) evidence, since we know the virus will be continually shed in the mouth," O'Donnell said. "So, the question now becomes, by how much could mouthwashes reduce viral load in the oropharynx of infected people, and if so, then for how long?"

Meyers noted that studies of people positive for COVID-19 using each product would be informative. It remains unknown, for example, if swishing, gargling, and/or spitting out mouthwash would add or decrease the efficacy demonstrated in the lab.

Listerine Antiseptic led the list of most effective mouthwashes for inactivating the coronavirus.

The study was published in the Journal of Medical Virology.

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