As Americans search for ways to fight the spread of the coronavirus, one popular topic that has generated interest on the internet is gargling. What’s behind the gargling claim, and is there any medical proof that gargling may help to fight coronavirus or other respiratory infections?
To date, as with many things in medicine, there has been no “gold standard” large-scale randomized controlled trial to confirm the effectiveness of gargling with salt water, vinegar or any other oral solutions to prevent upper and lower respiratory infections caused by coronavirus or any other virus or bacteria. Smaller studies have shown that mouthwash and various other liquids commonly used to gargle can kill microbes, but whether gargling actually prevents or treats disease has not been proven in rigorous trials.
Still, gargling is a common hygiene measure in many countries. In East Asia, particularly in Japan, gargling is strongly encouraged by the national government, along with other practices like hand-washing, wearing face masks and social distancing, as a matter of routine hygiene during the regular cold and flu season. (Not everyone, though, can gargle effectively, including some people with neck pain, stroke or dementia, as well as children generally under the age of 8.) Most of the early studies suggesting that gargling may help to prevent and treat upper and lower respiratory infections, not surprisingly, come from Japan.
The most intriguing findings center on the use of an over-the-counter povidone-iodine oral gargle solution, which has been commonly used for decades by people in Japan and elsewhere to treat a sore throat. In a small Japanese experimental study from 2002, 23 patients with chronic respiratory disease gargled four or more times a day with a povidone-iodine solution. Researchers found that, compared to the number of acute respiratory infections before the group started gargling, regular gargling for several months to two years with the povidone-iodine solution led to an approximate 50 percent reduction in the incidence of acute respiratory infections. Gargling with the solution led to a reduction in infections caused by some fairly virulent bacteria, among them Pseudomonas, Staph (including MRSA) and Haemophilus.
Laboratory studies have also suggested potential benefits from gargling, though a major limitation of these test-tube studies is that what works in the lab may not translate to health benefits for patients. A recent German lab study sponsored by a manufacturer of povidone-iodine sore throat gargle solution, for example, reported that the solution was shown to eliminate over 99 percent of the coronaviruses that cause SARS and MERS (very close cousins to the current Covid-19). An earlier Japanese lab study revealed that povidone-iodine products outperformed other common antiseptics such as chlorhexidine gluconate and benzalkonium chloride in inactivating many other common problematic viruses, such as coxsackie, rhinovirus, adenovirus, rotavirus, influenza, to name a few. Clinical trials in people would be needed to determine the clinical relevance for patients.
In the United States, povidone-iodine solutions are sold as skin disinfectants, which contain ingredients that can cause serious harm if ingested; preparations that are suitable for gargling are not generally available in this country. It’s critical that people not gargle with skin disinfectant solutions, including those that contain povidone-iodine. In Canada, a povidone-iodine gargle solution is sold under the brand name Betadine. Some people are allergic to iodine, however, and iodine can cause problems in patients with thyroid problems.
There is less evidence for the potential antimicrobial benefits of other gargle solutions. Listerine antiseptic, for example, has been shown to have antiviral activity in laboratory test-tube studies against some viruses that had been exposed for at least 30 seconds, though studies have not looked at coronavirus.
A recent intriguing clinical study from England involving 66 patients suggested that using a homemade hypertonic saline solution for nasal irrigation and gargling significantly reduced the incidence of flu and colds. (Some common colds are caused by coronaviruses, though they are far less dangerous than the strain of coronavirus that is currently circulating.) While nasal irrigation requires a sterile preparation, gargling does not. The gargling solution in the study involved a heaping teaspoon of salt in a cup of water to make an approximate 3 percent saline solution, gargled up to six times a day. A follow-up lab study by the same group of investigators discovered a potential mechanism of action of the saline solution, whereby throat cells took up extra chlorine from the saline solution to produce a compound that has known antiviral properties.
Other small studies have suggested potential beneficial anti-viral activity of gargling with green tea or solutions containing catechins, active ingredients of green tea, or with apple cider vinegar. These studies, however, were done in the laboratory, so have unknown clinical relevance for patients, and none looked at coronavirus specifically. One study even suggested that gargling with tap water alone may even be helpful in reducing the incidence of upper respiratory infections in a healthy population, although a later study did not confirm this finding.
Over all, looking at gargling from a risk-benefit ratio perspective, there seems to be little downside to frequent gargling. It’s a low-cost intervention, and may help to treat a sore throat. Whether gargling will actually fight off colds or flu, however, let alone the more serious coronavirus that is currently circulating, remains indeterminate as the current evidence base is limited.
Neal Naito, M.D., M.P.H., a former director of public health for the U.S. Navy, is a private practice health care consultant living in Maryland.
