A study published in the Journal of Medical Virology last month found that some common mouthwashes and nasal rinses could inactivate a type of human coronavirus in the lab. This led the authors to hypothesize that the same products might be an additional line of defense against SARS‐CoV‐2, the virus that causes COVID-19.
"While we wait for a vaccine to be developed, methods to reduce transmission are needed," research leader Dr. Craig Meyers of Penn State College of Medicine said in a press release. "The products we tested are readily available and often already part of people’s daily routines."
The idea behind the study is that using these products might reduce the amount of coronavirus spread by people who are infected.
The researchers tested several products including a neti pot, several popular mouthwashes and a one percent baby shampoo solution commonly used by head and neck doctors to rinse the sinuses. They exposed a human coronavirus to the various solutions for 30 seconds, one minute and two minutes. Then, they exposed human cells to the various solutions in order to determine how much of the virus had been inactivated.
The neti pot did not succeed in inactivating any virus, according to the study, but the shampoo solution inactivated more than 99 percent of the virus after 30 seconds and more than 99.9 percent of the virus after two minutes.
Several common mouthwashes were also very successful at inactivating the virus. Crest Pro Health, Listerine Ultra, CVS Antiseptic Mouthwash and Betadine 5% all inactivated 99.9 to greater than 99.9 percent of the virus after 30 seconds. Listerine Antiseptic was the most effective, inactivating more than 99.9 percent of the virus after 30 seconds.
Outside experts, however, cautioned against a too-enthusiastic response to the findings.
For one thing, the researchers did not test SARS-CoV-2 itself, which requires extra levels of training and security. Instead, they looked at 229E, a coronavirus that causes human colds, The New York Times reported. While it has a similar structure to the new coronavirus, it is not guaranteed that the two will always act the same way, Columbia University virologist Angela Rasmussen told The New York Times. However, Meyers pointed out in the press release that a similar study had managed to use mouthwashes to inactivate SARS-CoV-2 itself.
For another thing, it isn’t really possible to test if something will stop the spread of a virus until it is tested on the actual human mouth, which is more complicated than a petri dish. Yale University infectious disease expert Dr. Maricar Malinis told The New York Times that the effectiveness of the products could not be proved without clinical trials on human subjects. This is something the research team is now seeking funding to do, according to The Philadelphia Inquirer.
Finally, a mouthwash could never totally prevent an infected person from shedding virus because the virus would continue to replicate in their cells after the rinse.
"If you have virus in your lungs, you just cough it back up into your mouth," Thomas E. Rams, director of the oral microbiology testing lab at Temple University’s Kornberg School of Dentistry, told The Philadelphia Inquirer. "You’d have to be rinsing on such a frequent basis. And what I fear is that some people would think they don’t need masks because they gargled with Listerine."
Meyers said he is not proposing mouthwash as a replacement for measures like masks or social distancing, but rather another line of defense. And he acknowledged that it would only be effective for a limited amount of time.
"We have an educated guess because we know how long the virus takes to replicate in culture — 6 to 12 hours,'" Meyers told The Philadelphia Inquirer.
