Listerine is a Mouthwash, Not An Antiviral Drug

Listerine is a Mouthwash, Not An Antiviral Drug

There are numerous “treatments” that can be found online on how to defeat the coronavirus. And although some of them may contain a grain of truth, unfortunately no treatments are available.
Can gargling with Listerine be helpful in reducing the risk of coronavirus infection? This is one of the many questions that have been raised by the growing army of straw doctors. After all, we know the classic slogan “Kills Germs by Millions on Contact”. Are viruses not germs? Yes, they are, but the slogan was coined in reference to bacteria in the mouth. Having said that, Listerine does indeed have some antiviral effects. At least in the test tube.

Before we get to that, a little history. Have you ever wondered how Listerine got its name? Joseph Lawrence, an American doctor, developed the well-known yellow liquid at the end of the 19th century and named it after the brilliant British surgeon Joseph Lister. No, Lister did not have bad breath. The product was named in his honour because Lister is generally considered the father of antisepsis, the science of infection prevention.

Lister knew that the kind of fractures that pierced the skin often became infected, while those that did not pierce the skin healed well. The prevailing opinion at the time was that exposed tissues were affected by atmospheric oxygen. It would break down the organic matter in a wound and produce pus. In an attempt to exclude oxygen, the usual practice was to bandage the wound with tight bandages. In fact, these bandages encouraged bacterial growth and led to a virtually indescribable stench on the wards. Many doctors believed that the stench caused the infections and was directly responsible for the extremely high mortality rate after surgery. Incongruently, however, nobody tried to solve the problem by eliminating the smell. The only voice of light in the darkness belonged to Florence Nightingale, the legendary “Lady with the Lamp”, who advocated a doctrine of soap, warm water and sunshine, but was largely ignored.

Then came a breakthrough. A professor of chemistry, Thomas Anderson, introduced Lister to the ideas of Louis Pasteur, who had shown that decay and fermentation can occur in the absence of oxygen as long as microorganisms are present. Furthermore, the microorganisms could be killed by heat. This really hit Lister, who had never believed in the oxygen theory anyway. In fact, he had imagined a kind of invisible dust that would settle in wounds. Lister immediately designed an experiment. He took some fresh urine, heated it and sealed half of it in a glass tube, with the other half exposed to the air. When he smelled the samples in the morning, the one exposed to the air stank, while the sealed sample was odorless. Obviously microorganisms from the air had infected the open sample.

Since heating a patient was obviously not a practical approach, he wondered whether the germs could be killed with suitable chemicals. Lister thought of carbolic acid or phenol because he knew that it had been used to clean foul-smelling sewers. He also knew that if the treated sewage was used as fertiliser, the cows grazing on the pastures would not be infested with parasites as usual. Perhaps the stuff that destroyed the smell and the parasites could also kill Pasteur’s microorganisms!

Lister got some carbolic acid from Anderson and tried it on a boy who had been run over by a cart and had an exposed tibia fracture. He recovered without complications. Lister soon washed his instruments with phenol and also developed a sprayer that could fill the operating room with a mist of disinfectant. The results were immediate; mortality due to amputations fell from 50 to 15%. Nevertheless, Lister had to face great skepticism because the germs or “small animals”, as some scornfully called the microbes, were not easy to observe. But in 1867, the renowned British journal The Lancet accepted Lister’s articles on the prevention of infection and the era of antisepsis was underway. Phenol would save thousands of lives.


But don’t look for phenol in Listerine today. The “active ingredients” are thymol, eucalyptol, menthol and methyl salicylate, vegetable essential oils with some antiviral properties. As early as 1995, researchers at the Houston Health Science Center of the University of Texas treated laboratory strains of the influenza A virus with Listerine for 30 seconds and found that the infectivity was eliminated. In other words, the treated virus could not infect cells. This was a laboratory study and it was never shown to have any clinical significance. However, it is interesting to note that the influenza A virus, just like SARS-CoV-2, is an enveloped RNA virus. Of course, there is absolutely no evidence that gargling with Listerine has any effect on the prevention of COVID-19, but at least it is a harmless activity and not as ridiculous as some of the other suggestions we have seen, such as snorting cocaine or drinking bleach . And one last word. There is some information circulating about the use of listerine for hand washing, because it contains alcohol. It contains alcohol, but only about 23%, which is not effective as a disinfectant.


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