How does mouthwash kill Covid-19?

While the world waits for the first Covid vaccines to be distributed, lab tests show that the virus can be killed by some supermarket mouthwashes.

This opens up the possibility that mouth-washing could help to slow the spread of the virus.

But experts said there is as yet no compelling evidence from human studies, and that mouthwashes are not a cure for those with the disease.

What is the evidence that mouthwashes can kill the virus?

Several independent teams of researchers in Germany and the US reported that some over-the-counter products rapidly destroy the Covid virus. Now a team at Cardiff University has published preliminary findings supporting the idea that using mouthwash might provide additional protection against infection.

In laboratory tests designed to mimic conditions in the mouth, the team found that three products – Dentyl Dual Action, Dentyl Fresh Protect and Listerine Advanced Gum Treatment – effectively eliminated the virus. The first two contain the antiseptic cetylpyridinium chloride (CPC), which the researchers believe shows “promising signs” of being able to destroy the Covid virus.

These products join others that have shown encouraging results in lab tests (see table)

However, the Cardiff researchers emphasised that the laboratory findings need to be confirmed in human trials.

But is gargling not already known to be useless?

Early in the pandemic, claims appeared on social media that gargling could cure people infected with Covid-19. Experts pointed out that infection involves the virus entering cells deep in the throat and lungs – beyond the reach of such simple measures.

The new research focuses solely on the possibility that mouthwashes might kill the virus just after it has entered the body, but before serious infection takes hold.

So if it is not a cure, what is the point ?

Slowing the spread of the Covid virus is critical if the pandemic is to be controlled without destroying the economy. If confirmed, the new findings open up the prospect of mouth-washing acting like a “chemical mask”, to be used in addition to standard masks, social distancing and hand-washing.

Some researchers believe slowing the spread of the virus also requires nasal washing. Two compounds already identified as potentially effective as a nasal spray against Covid-19 are 0.5 per cent povidone iodine solution and 1 per cent Johnson’s baby shampoo.

When will we see the results of human trials?

At least half a dozen are already under way, but they all involve small numbers of patients, and so are unlikely to produce compelling evidence.

Very early results from some studies suggest that mouth-washing may be effective outside lab conditions; but the results are inconsistent. They also fail to resolve key questions such as the precise concentrations needed and how long the mouthwashes remain effective once in the mouth.

Why is it all taking so long?

Evidence for the effectiveness of mouth-washing against respiratory diseases such as Covid-19 has been circulating for at least a decade. Listerine was identified as potentially useful during the Spanish flu pandemic a century ago.

However, the studies are generally small and poor quality, and have been widely dismissed or mis-interpreted.

Some researchers also suspect the mouth-washing idea has suffered because it lacks the hi-tech glamour of vaccines – despite its promise as a simple and low-cost means of slowing the spread of the virus.