Still, the researchers theorize that the fatty shell encasing the coronavirus can be broken down by certain mouthwash ingredients -- including grain alcohol; chlorhexidine, a long-lasting form of iodine; and hydrogen peroxide. The idea is supported, they say, by published studies of other enveloped viruses, including the coronaviruses that cause the common cold.
But even if mouthwash temporarily killed off coronavirus in the mouth and upper throat, that doesn't mean it would reduce the spread of COVID-19. Coronavirus infection can be spread in droplets coughed by a sick person, but people who have no symptoms and even some people who have recovered still release the virus when they breathe or speak. Public health experts say that washing your hands and not touching your face will reduce transmission.
"Although all these mouthwash chemicals may have activity against the coronavirus, none protect against transmission," Wolff said. "If you touch your eyes or nose, the mouthwash isn't helping with that."
There have been some randomized clinical trials. One involved 19,500 Japanese nursery school tykes. Half of them gargled at least once a day with green tea, ozone water, or salt water to see if it would prevent fevers and school absences. The garglers developed fewer fevers than the non-garglers, but school absences were about the same in both groups.
Another Japanese trial looked at whether gargling three times a day with long-lasting iodine or water could prevent upper respiratory infections in adults. Plain old tap water was modestly effective.
"Rinsing with iodine is effective against bacteria, but tastes disgusting," Wolff noted.
Because dentistry is all about working in patients' mouths, dentists need to be extra careful about personal protective gear, cleaning, and screening patients. As for mouthwash, the American Dental Association advises that dentists may want to have patients use a mouthwash with very diluted hydrogen peroxide or long-lasting iodine before a procedure.
The ADA adds this caveat: "There are no clinical studies supporting the virucidal effects of any pre-procedural mouthrinse against" the coronavirus.
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