Dr Fauci — the US Government's top infectious diseases expert — said that it was 'common sense' that double-masking would be more effective.
He added it was 'likely' to offer better protection against the mutant strain, which studies show partially evades immunity from vaccines and past infections.
And Dr Benjamin Killingley, a scientist advising the UK Government in the pandemic, also said wearing two masks was 'common sense'.
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But Dr Killingley, a member of the SAGE advisory group, also admitted the claim isn't 'grounded in lots of study'.
Other experts have warned there is no firm evidence to prove double-masking works although they say it sounds like a 'good idea'.
Professor Cath Noakes — a mechanical engineer at the University of Leeds who advises the government on airborne infections — said wearing two layers of fabric over your face could be uncomfortable.
Face masks have been widespread all over the world during the pandemic and can stop Covid spreading by blocking infectious droplets, which are expelled through coughs, sneezes or speech. They are not perfect, however, and some tiny droplets can still make it past masks and people may also spread the virus on their hands.
Dr Fauci signalled his backing for double-masking yesterday, telling US programme Today: 'It just makes common sense that it likely would be more effective.
'You know it likely does [stop infection] because this is a physical covering to prevent droplets and virus to get in.
Dr Killingley, an infectious disease expert at University College London, said it was 'common sense' that wearing two masks made someone less likely to spread the virus.
But he told the Daily Telegraph this was not 'grounded in lots of study... not because there's evidence one way or the other, there just isn't really great evidence.'
hello twitter i’m about to go to my college for the first time and i’m jjst very excited and wanted to share!! i’m all set with two masks, gloves, and a face shield. i may look ugly but at least i’m safe 🤪 pic.twitter.com/m4VQXNuRe1— freak 4 the earth (@nomibalogna) February 4, 2021
He added if one mask reduces droplets leaving someone's mouth by 80 per cent, wearing another mask on top of that would cut that remaining 20 per cent by another 80 per cent.
The added 16 per cent protection could mean that only four per cent of droplets actually escaped from someone's mouth, he suggested, which could make the double-masking worthwhile.
'My stance on it is that I never say to people don't wear two face masks if you really want to, but it's got to be comfortable, wearing two face masks is a bit tighter, it's a bit hotter.'
Professor Noakes, an environmental engineering expert at Leeds University, told BBC Radio 4's Today programme double-masking 'achieves' some additional protection.
'In a way that achieves some of that (protection) because you're providing different materials and you're doubling up on how it fits around your face,' she said.
'I would caution a little bit there though, I mean it could start to get quite uncomfortable.
'The more you've got there the harder it is to breathe through those masks together; it's going to be fairly uncomfortable around your ears and you also probably need to think about the hygiene of two masks as opposed to just one but in theory it will provide a greater degree of protection.'
It comes after the UK recorded another 14,104 infections yesterday, prompting the Health Secretary Matt Hancock to claim the country is 'turning a corner in our battle against the virus'.
A further 333 Covid-19 deaths were also announced, the lowest 24-hour toll since December 27 and a drop of 18 per cent from the previous Monday.
The US recorded its lowest number of daily cases since October yesterday with 77,737, with 38 states also seeing hospitalisations fall by at least 10 per cent.
But the country's Centers for Disease Control and Prevention warned the downward trend could easily be reversed by new variants.
© Associated Newspapers Ltd.