Human coronaviruses ‘inactivated’ by mouthwash, oral rinses: study

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A new study conducted by researchers at the Penn State College of Medicine has found that a common dental item can inactivate human coronaviruses: mouthwash and oral rinses. 

For the study, the results of which were published in the Journal of Medical Virology, researchers tested various oral and nasopharyngeal rinses — which included a 1% solution of baby shampoo, a neti pot, peroxide sore-mouth cleansers, and mouthwashes — to determine how well they inactivated human coronaviruses, namely 229e, a strain that can cause the common cold.  

“While we wait for a vaccine to be developed, methods to reduce transmission are needed,” Meyers said in a statement. “The products we tested are readily available and often already part of people’s daily routines.” (iStock)

Human volunteers were not used in the study; the 229e coronaviruses were grown in human liver cells in the lab before being immersed in the various solutions tested as part of the study.

The baby shampoo solution, “which is often used by head and neck doctors to rinse the sinuses,” the researchers noted in a news release regarding the findings, was particularly effective; the solution inactivated “greater than 99.9% of human coronavirus after a two-minute contact time,” they said. 

The mouthwash and oral rinses tested —  which included Listerine Antiseptic, Orajel Antiseptic Rinse, and Crest Pro‐Health, among others — were also efficacious, they found: "Many inactivated greater than 99.9% of virus after only 30 seconds of contact time and some inactivated 99.99% of the virus after 30 seconds.” 

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More specifically, researchers “used a test to replicate the interaction of the virus in the nasal and oral cavities with the rinses and mouthwashes,” as the nasal and oral cavities are thought to be main points of entry for human coronaviruses, including SARS-CoV-2, better known as COVID-19. Though the researchers didn’t specifically test SARS-CoV-2 in the study, the novel virus is genetically similar to the other human coronaviruses tested, leading the researchers to hypothesize the results could be similar. 

A strain of human coronavirus was mixed with “baby shampoo solutions, various peroxide antiseptic rinses and various brands of mouthwash,” allowing the solutions to interact with the virus for different amounts of time, including 30 seconds, one minute, and two minutes. The solutions were then diluted to “prevent further virus inactivation,” they wrote. 

“To measure how much virus was inactivated, the researchers placed the diluted solutions in contact with cultured human cells. They counted how many cells remained alive after a few days of exposure to the viral solution and used that number to calculate the amount of human coronavirus that was inactivated as a result of exposure to the mouthwash or oral rinse that was tested,” per the news release. 

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Lead study author Craig Meyers, a distinguished professor of microbiology and immunology and obstetrics and gynecology, said the results show the amount of virus (viral load) in an infected person’s mouth could be reduced by using these common over-the-counter products, possibly helping to reduce the spread of the novel virus. 

“While we wait for a vaccine to be developed, methods to reduce transmission are needed,” Meyers said in a statement. “The products we tested are readily available and often already part of people’s daily routines.”

The team’s findings bolster past research that also looked at how oral rinses and mouthwashes may be able to reduce the viral load of human coronaviruses. For instance, a study published in the scientific journal Function in May also concluded mouthwash could play a role in preventing the transmission of the novel coronavirus. 

Additionally, a more recent study published in The Journal of Infectious Diseases in August came to a similar conclusion. Meyers said that his findings add to this research, noting his team evaluated the solutions at longer contact times in addition to studying over-the-counter products and nasal rinses that were not evaluated in the other study.

However, Toni Meister of Ruhr University Bochum in Germany, who led the study published in The Journal of Infectious Diseases, warned the findings do not mean mouthwash on its own can treat COVID-19. Indeed: "Gargling with a mouthwash cannot inhibit the production of viruses in the cells," Meister said at the time, "but could reduce the viral load in the short term where the greatest potential for infection comes from, namely in the oral cavity and throat — and this could be useful in certain situations, such as at the dentist or during the medical care of COVID-19 patients."

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Meyers echoed this sentiment. 

“People who test positive for COVID-19 and return home to quarantine may possibly transmit the virus to those they live with,” said Meyers. “Certain professions including dentists and other health care workers are at a constant risk of exposure. Clinical trials are needed to determine if these products can reduce the amount of virus COVID-positive patients or those with high-risk occupations may spread while talking, coughing or sneezing. Even if the use of these solutions could reduce transmission by 50%, it would have a major impact.”