People wearing a face mask "might actually promote immunity" against COVID-19 in the population, Professor Luke O'Neill has said.
The leading immunologist says evidence is starting to support a hypothesis that being put forward by scientists about a potential extra benefit to face coverings.
Last week, an article published in the prestigious New England Journal of Medicine put forward the idea that universal facial masking "might help reduce the severity of disease and ensure that a greater proportion of new infections are asymptomatic".
On today's Pat Kenny Show, Professor O'Neill - professor of biochemistry at Trinity College Dublin - explained the "really interesting" idea.
He said: "We know masks work - the scientific evidence is so compelling now. Anybody who denies masks... show me the scientific evidence against it, because the evidence on the other side is so strong.
"Now they're saying there's something else about masks: it may well actually promote immunity.
"You might wonder how the hell can a mask make someone immune. Masks aren't perfect... so tiny bits of virus get out, and sadly infect someone else.
"But guess what: they have a very mild infection, almost with no symptoms... they don't even know they have it... and now they might be protected."
'There's some evidence to support this'
Professor O'Neill said the idea is 'a bit like' how a vaccine works, where people are exposed to a weaker version of the virus so their immune system learns to fight against it.
He said: "There's some evidence to support this. There was an Argentinian cruise ship, and they put masks on people because there was an infection. Of those who did get infected, 80% were asymptomatic.
"On another cruise ship, [where passengers] didn't wear masks, only 20% were asymptomatic.
"It's seen as another reason to wear masks - it might actually promote immunity in the population.
"Anybody who says 'don't wear a mask'... tell them this evidence."
He pointed to a recent study involving hamsters, where a mask was put in the middle of a cage.
He explained: "The ones on the far side didn't really get infected if there was a mask between them. There was a very low infection. If they did get infected, it was asymptomatic.
"In other words, a bit of virus got through the mask... a tiny level of infection... and they got no symptoms.
"That's animal, not humans obviously - but it's still good evidence. It's almost as if a tiny bit of virus is quite good, because it might provoke no symptoms and a bit of immunity.