A new study from the Penn State College of Medicine is the latest to show that some oral mouthwashes, and even a diluted solution of baby shampoo, can kill up to 99.9% of coronaviruses.

But you might want to hold off on cornering the mouthwash market. The experiment was done in the lab, not with humans. The Penn State study, published in the Journal of Medical Virology, also did not use SARS-CoV-2, the virus that causes COVID-19, because that requires a high biosecurity lab; it tested a strain of coronavirus of similar structure.

The virus spread

Coronaviruses, including SARS-CoV-2, use the mouth and nose as the main entry points into the body. The virus can also enter the body through the eyes.

It is spread through aerosol droplets that we emit when we sneeze or cough. That’s why public health agencies like the Centers for Disease Control and Prevention (CDC) and the World Health Organization (WHO) recommend wearing a mask in public, social distancing and avoiding large crowds. The question then is, can swishing mouthwash or using a nasal spray at least help reduce the chance of getting sick?

The study

The Penn State team, led by Craig Meyers, PhD, professor of microbiology and immunology and obstetrics and gynecology, set out to answer that. The researchers evaluated a 1% solution of baby shampoo, peroxide sore-mouth cleansers and mouthwashes. Each solution was tested on human cells for intervals of 30 seconds, one minute and then two minutes.

The researchers found that the diluted baby shampoo rinse “reduced the amount of infectious virus by close to 99% after a contact time of one minute and greater than 99.9% after contact time of two minutes.”

Most of the tested, over-the-counter mouthwashes neutralized 90% of the virus, but some were able to kill 99.9% when in contact for 30 seconds and two minutes. Dr. Meyers told The Philadelphia Inquirer that the study’s findings are not meant as a replacement for masks and social distancing, but rather as another layer of protection.

“While we wait for a vaccine to be developed, methods to reduce transmission are needed,” Dr. Meyers told Science Daily. “The products we tested are readily available and often already part of people’s daily routine.”

But many physicians and scientists are skeptical about the value of the mouthwash research. They point out that you would have to swish mouthwash almost continuously for it to be effective.

“I don’t have a problem with using Listerine,” Angela Rasmussen, PhD, a virologist at Columbia University, told The New York Times. “But it’s not an antiviral.”

Even virologists at Ruhr-Universitat Bochum in Germany, who have used commercially available mouthwashes to kill the SARS-CoV-2 virus, said the use of mouthwashes to prevent COVID-19 could be helpful prior to dental treatments, but not for treating or protecting yourself from the virus.

“Gargling with a mouthwash cannot inhibit the production of viruses in the cells, 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,” Toni Meister, the German team leader, said in a press release. “And this could be useful in certain situations, such as at the dentist or during the medical care of Covid-19 patients."

On Facebook, the WHO made it clear that gargling with mouthwash will not protect people from COVID-19. “There is no evidence that using mouthwash will protect you from infection with the new coronavirus,” read the post. “Some brands of mouthwash can eliminate certain microbes for a few minutes in the saliva in your mouth. However, this does not mean they protect you from [COVID-19]."

Robert Calandra is an award-winning journalist, book author and playwright. His work has appeared in national and regional magazines and newspapers.