Can gargling with Listerine be of any help in reducing the risk of coronavirus infection? That is one of the numerous questions that has been raised by the increasing army of straw-clutchers. After all, we are familiar with the classic slogan, “Kills Germs by Millions on Contact.” Aren’t viruses germs? Yes, they are, but the slogan was coined in reference to bacteria in the mouth. With that being said, Listerine does actually have some antiviral effects. At least in the test tube.
Before getting around to that, a little history. Ever wonder how Listerine got its name? Joseph Lawrence, an American physician, developed the familiar yellow liquid in the late 1800s 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 widely considered to be the father of antisepsis, the science of preventing infections.
Lister knew that the type of fractures that broke through the skin would often become infected whereas those that did not pierce the skin healed nicely. The prevailing opinion at the time was that the exposed tissues were affected by oxygen in the air. It would break down the components of organic matter in a wound and generate pus. In an attempt to exclude oxygen, the common practice was to dress the wound with tight bandages. Actually, these dressings encouraged bacterial growth and resulted in a virtually indescribable stench in the wards. Many doctors believed that the stench caused the infections and that it was directly responsible for the extremely high death rate following surgery. Yet, incongruously, nobody tried to solve the problem by eliminating the smell. The sole voice of light in the darkness belonged to Florence Nightingale, the legendary "lady with the lamp," who espoused 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 rotting and fermentation could occur in the absence of oxygen, as long as microorganisms were present. Furthermore, the microorganisms could be killed by heat. This really struck a chord with Lister who had never believed in the oxygen theory anyway. Indeed, he had fantasized about some sort of invisible dust settling into wounds. Lister immediately designed an experiment. He took some fresh urine, heated it and sealed half of it in a glass tube, leaving the other half exposed to the air. When he smelled the samples in the morning, the one that had been exposed to the air reeked while the sealed sample was odorless. Evidently microorganisms from the air had infected the open sample.
Since heating a patient was of course not a viable approach, he wondered if the germs could be killed with appropriate chemicals. Lister thought of carbolic acid, or phenol because he knew that it had been used to cleanse foul-smelling sewers. He also knew that when the treated sewage was used as fertilizer, the cows grazing on the pastures did not become infested with parasites, as was commonly the case. 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 fracture of the tibia. He recovered with no complications. Soon Lister was washing his instruments with phenol and also developed a sprayer that could fill the operating room with a mist of the disinfectant. The results were immediate; mortality from amputations dropped from 50 to 15%. Nevertheless, Lister had to deal with a great deal of skepticism because the germs, or "little beasts" as some scornfully called the microbes, were not readily observable. But in 1867, The prestigious British Journal The Lancet accepted Lister's article on the prevention of infections 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, plant essential oils that do have some antiviral properties. Back in 1995, researchers at the University of Texas Houston Health Science Center treated laboratory strains of influenza A virus with Listerine for thirty seconds and found that infectivity was eliminated. In other words, the treated virus was unable to infect cells. This was a laboratory study and was never shown to have any clinical importance. It is, however, interesting to note that influenza A virus is an enveloped RNA virus just like SARS-CoV-2. Of course, there is no evidence at all that gargling with Listerine has any effect on preventing COVID-19, but at least it is a harmless activity and not as ridiculous as some of the other proposals we have seen such as snorting cocaine or drinking bleach. And a final word. There is some information circulating about using Listerine as a hand wash since it contains alcohol. It does contain alcohol, but only about 23% which is ineffective as a disinfectant.
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