Face masks can prevent the spread of COVID-19, and this has also been established in a preliminary analysis of 194 countries.
In the analysis, it was found that places where face masks weren't recommended, witnessed a 55 per cent weekly increase in COVID-19 deaths per capita after their first case was reported.
Countries with cultures or guidelines supporting face masks-wearing, however, witnessed a 7 per cent for the same period.
A model from the University of Washington predicted that the US could prevent at least 45,000 COVID-19 deaths by November if 95 per cent of the population were to wear face masks in public.
But not all masks confer equal levels of protection.
The ideal face mask blocks large respiratory droplets from coughs or sneezes – the primary method by which people pass the coronavirus to others – along with smaller airborne particles, called aerosols, produced when people talk or exhale.
The World Health Organisation (WHO) recommends medical masks for healthcare workers, elderly people, people with underlying health conditions, and people who have tested positive for the coronavirus or show symptoms.
Healthy people who don't fall into these categories should wear a fabric mask, according to WHO.
The Centres for Disease Control and Prevention also recommends cloth masks for the general public.
But even cloth masks vary since certain types are more porous than others.
Citing a report by Business Insider, Science Alert quoted Dr Ramzi Asfour as saying, "It depends on the quality."
"If you're making a cloth mask from 600-thread-count Egyptian cotton sheets, that's different than making it from a cheap T-shirt that's not very finely woven," added Dr Asfour, an infectious-disease physician in Marin County, California.
It may be mentioned here that scientists, over the past few months, have been evaluating the most effective mask materials for trapping the coronavirus.
There's a reason agencies recommend reserving N99 and N95 masks for healthcare workers first: Both seal tightly around the nose and mouth so that very few viral particles can seep in or out.
They also contain tangled fibres to filter airborne pathogens.
A recent study published in the Journal of Hospital Infection evaluated over 10 masks based on their ability to filter airborne coronavirus particles.
It was found that N99 masks reduced a person's risk of infection by 94 to 99 per cent after 20 minutes of exposure in a highly contaminated environment.
N95 masks offered almost as much protection- the name refers to its minimum 95 per cent efficiency at filtering aerosols.
Another recent study also determined that N95 masks offered better protection than surgical masks.
Surgical masks are made of nonwoven fabric, so they're usually the safest option for healthcare workers who don't have access to an N99 or N95 mask.
An April study found that surgical masks reduced the transmission of multiple human coronaviruses (though the research did not include this new one, officially called SARS-CoV-2) through both respiratory droplets and smaller aerosols.
In general, surgical masks are about three times as effective at blocking virus-containing aerosols than homemade face masks, a 2013 study found.
But healthcare workers should still have access to them first.
In a recent paper that hasn't yet been peer-reviewed, researchers in the UK determined that "hybrid" face masks – combining two layers of 600-thread-count cotton with another material like silk, chiffon, or flannel – filtered more than 80 per cent of small particles (less than 300 nanometres) and more than 90 per cent of larger particles (bigger than 300 nanometres).
They found that the combination of cotton and chiffon offered the most protection, followed by cotton and flannel, cotton and silk, and four layers of natural silk.
The researchers suggested that these options may even be better at filtering small particles than an N95 mask, though they weren't necessarily better at filtering larger particles.
WHO recommends that fabric masks have three layers: an inner layer that absorbs, a middle layer that filters, and an outer layer made from a nonabsorbent material like polyester.
A University of Illinois study that's still awaiting peer review found three layers of either a silk shirt or a 100 per cent cotton T-shirt may be just as protective as a medical-grade mask.
Silk, in particular, has electrostatic properties that can help trap smaller viral particles.
The Journal of Hospital Infection study found that vacuum-cleaner bags (or vacuum-cleaner filters inserted in a cloth mask) reduced infection risk by 83 per cent after 30 seconds of exposure to the coronavirus and by 58 per cent after 20 minutes of exposure in a highly contaminated environment.
The material was almost as good at filtering aerosols as surgical masks, the researchers found.
That could be enough protection to stop an outbreak. A May study found that universal mask-wearing would bring an epidemic under control even if the masks were only 50 per cent effective at trapping infectious particles.
The next-best alternatives to vacuum-cleaner bags or filters were tea towels and antimicrobial pillowcases, the study revealed.
Tea towels need to be tightly woven to confer protection, the researchers said.
Antimicrobial pillowcases (usually made of satin, silk, or bamboo) were preferable to a standard cotton pillowcase, they found.
Wrapping a scarf or cotton T-shirt around your nose and mouth isn't particularly effective at filtering the coronavirus, but it's still better than nothing.
The UK researchers found that a single layer of 80-thread-count cotton was among the least effective materials at blocking coronavirus particles both large and small.
Scarves and cotton T-shirts reduced infection risk by about 44 per cent after 30 seconds of exposure to the coronavirus, the study found.
After 20 minutes of exposure in a highly contaminated environment, that risk reduction dropped to just 24 per cent.
Even a loosely fitted cotton mask "substantially decreases" the spread of viral particles when an infected person coughs or sneezes, researchers in India recently determined.
They found that infectious droplets travelled up to 16 feet when a person wasn't wearing a mask, compared with just 5 feet when particles leaked out the sides of a face mask.
Single-layer cotton masks are preferable to single-layer paper masks.
The UK researchers found that people who wore cotton masks had a 54 per cent lower chance of infection than people who wore no masks at all. People who wore paper masks had a 39 per cent lower chance of infection than the no-mask group.
Unlike a surgical mask, which is typically pleated and made of three layers of fabric, paper masks are thinner, so they confer less protection.
The protectiveness of a mask – including N95 and surgical masks – declines considerably when there is a gap between the mask and the skin.
Researchers have said it over and over again that one has to make sure that there's no air leak.
Even so, research has suggested that wearing masks improperly or sporadically could still reduce transmission.
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