The debate over which type of face mask to wear to the supermarket has become a hot topic. Is a fashionable one-layer mask adequate? Are filters a good idea, or a needless expense?
In an attempt to find an answer, scientists at Duke University in North Carolina carried out a study on 14 different types of face coverings being used during the pandemic.
Their study spanned the type of mask worn by healthcare professionals in hospital settings to the neck scarves worn by some celebrities while out and about in recent months.
It found that an N95 mask, which features a filter allowing it to remove 95 per cent of airborne particulates, was the most effective.
The second most effective type of face covering was found to be the standard-issue three-layer protection mask, or a mask made of cotton - such as the homemade varieties being made and sold.
In a surprising discovery, neck fleeces were found to make the wearer more likely to transmit Covid-19 to others than if they had worn no mask at all.
The study authors explained that neck fleeces are so ineffective because the type of material breaks down large droplets into smaller particles, which are then spread more easily into the air around the wearer's mouth.
To carry out their study, the Ivy League university researchers compared the dispersal of droplets from participants’ breath while wearing each one of the face coverings with the results of a control trial, which saw a participant breath without any form of mask.
The researchers found that the neck fleece saw an average “droplet transmission fraction” of 110 per cent.
Overall they found the material used to make different types of masks was a crucial factor, with knitted masks less effective than cotton ones on average, while shape also has an impact. Bandanas, for example, were found to be less effective than traditional mask shapes.
Researcher Martin Fischer, who put the test together, told CNN: "We were extremely surprised to find that the number of particles measured with the fleece actually exceeded the number of particles measured without wearing any mask.”
He added: “We want to emphasise that we really encourage people to wear masks, but we want them to wear masks that actually work."
At the height of the first wave of Covid-19 it was almost impossible to source N95 masks in the UK, and even today many NHS staff wear three-layer protection masks unless they are working in a Covid ward, or directly with Covid-positive patients.
Mask wearing has become mainstream in the UK for the first time as a result of the Covid-19 pandemic.
On June 15 it became mandatory to wear a mask on all forms of public transport, and since July 24 it has been compulsory to wear a mask in all shops, with other indoor settings added to the list from August 8.
Wearing a face covering in public was already common in some Asian countries, such as South Korea and Japan, as the practise was taken up following the SARS-COV-2 outbreak in the early 2000s.
Masks are generally thought to help suppress the spread of disease, and are seen as a socially responsible move, as the wearing of a mask prevents transmission and protects those around the wearer rather than the wearer themselves.
However, not all epidemiologists agree that mask-wearing is essential to help prevent the spread of viruses such as Covid-19.
The expert in charge of Sweden's coronavirus response has dismissed the scientific evidence for mask-wearing as "astonishingly weak".
Sweden has not mandated masks be worn in public spaces, with cafes and bars left open throughout the pandemic. Anders Tegnell old Swedish newspaper Bild this week that “the findings that have been produced through [the use of] facemasks are astonishingly weak”.
He added: “I’m surprised that we don't have more or better studies showing what effect masks actually have. Countries such as Spain and Belgium have made their populations wear masks but their infection numbers have still risen. The belief that masks can solve our problem is in any case very dangerous."
