Wearing a cloth mask may not shield the user from coronavirus because too many infected droplets can slip through, a study has claimed.
Scientists at New Mexico State University, in the US, studied five types of face coverings including cloth masks and surgical grade N95 masks.
They found that while all masks blocked at least 95 per cent of droplets from coughs and sneezes – there was still a risk of the disease being passed on.
Although cloth masks stopped 96.4 per cent of sneeze droplets at a distance of six feet, they still let more than 1,000 through – which the scientists said could carry enough virus particles to trigger an infection.
‘Wearing a mask will offer substantial, but not complete, protection to a susceptible person,’ said Dr Krishna Kota, an associate professor at the university who led the research.
The science behind mask-wearing was hazy at the start of the pandemic and authorities in the UK and other countries hesitated to recommend wearing them.
The World Health Organization did recommend masks until June 8, and then only for people over 60 and those with underlying health conditions.
In Britain, face coverings were first brought in for public transport in June, and later for shops and other indoor spaces in July. In the US regulations vary across the country, with some states setting up rules as early as April but others resisting making masks mandatory.
The general consensus now is that masks may offer only limited protection to the people wearing them, but they are quite good at stopping people spreading the disease if they have it without knowing, because they catch their breath.
Scientists have also suggested that masks could reduce severity of disease by exposing people to the virus in small doses, but this hasn’t been proven.
Five types of face masks were examined with results showing that the N95 (top right) blocked the most at 100% of droplets and the regular cloth mask (bottom left) blocked the least at 96.4% of droplets
‘A mask definitely helps, but if the people are very close to each other, there is still a chance of spreading or contracting the virus,’ said Dr Kota.
‘It’s not just masks that will help. It’s both the masks and distancing.’
For the study, published in the journal Physics of Fluid, the team built a machine that mimics coughs and sneezes from humans.
It uses an air generator to blow tiny liquid droplets, like those that would escape from a nose or a mouth.
The machine was tested on five different types of masks: an N95 mask, s surgical mask, a cloth mask, a two-layer cloth mask and a wet two-layer cloth mask.
The researchers say wetting a mask could help because the material’s fibers will expand, reducing the pore size accessible for droplets to get through.
Two glass square tubes were joined with a mask tightly fit between them and a camera lens to capture the number of droplets.
Each of the masks were able to block most of the droplets with the best-performing being the N95, which blocked 100 percent of droplets.
Meanwhile, the worst was the regular cloth mask, which only blocked 96.4 percent of the droplets from getting through.
However, at distances of less than six feet, letting in around three percent of droplets could be enough to make someone ill.
Studies have shown that the average infection threshold for COVID-19 is 1,000 virus particles, inhaled either all at once or on separate occasions.
In addition, a single sneeze has the potential to carry up to 200 million virus particles.
The cloth mask let through more than 1,000 sneeze droplets, each of which could have millions of virus particles.
The two-layered cloth mask with a PM2.5 filter let through more than 600 sneeze droplets.
This means that if someone wearing one of these masks is close to an infected individual, enough droplets could escape to make them contract COVID-19.
‘Without a face mask, it is almost certain that many foreign droplets will transfer to the susceptible person,’ Kota said.
‘Wearing a mask will offer substantial, but not complete, protection to a susceptible person by decreasing the number of foreign airborne sneeze and cough droplets that would otherwise enter the person without the mask.
‘Consideration must be given to minimize or avoid close face-to-face or frontal human interactions, if possible.’
THE TRUTH ABOUT FACE MASKS: WHAT STUDIES HAVE SHOWN
Research on how well various types of masks and face coverings varies but, recently, and in light of the pandemic of COVID-19, experts are increasingly leaning toward the notion that something is better than nothing.
A University of Oxford study published on March 30 concluded that surgical masks are just as effective at preventing respiratory infections as N95 masks for doctors, nurses and other health care workers.
It’s too early for their to be reliable data on how well they prevent infection with COVID-19, but the study found the thinner, cheaper masks do work in flu outbreaks.
The difference between surgical or face masks and N95 masks lies in the size of particles that can – and more importantly, can’t – get though the materials.
N95 respirators are made of thick, tightly woven and molded material that fits tightly over the face and can stop 95 percent of all airborne particles, while surgical masks are thinner, fit more loosely, and more porous.
This makes surgical masks much more comfortable to breathe and work in, but less effective at stopping small particles from entering your mouth and nose.
Droplets of saliva and mucous from coughs and sneezes are very small, and viral particles themselves are particularly tiny – in fact, they’re about 20-times smaller than bacteria.
For this reason, a JAMA study published this month still contended that people without symptoms should not wear surgical masks, because there is not proof the gear will protect them from infection – although they may keep people who are coughing and sneezing from infecting others.
But the Oxford analysis of past studies- which has not yet been peer reviewed – found that surgical masks were worth wearing and didn’t provide statistically less protection than N95 for health care workers around flu patients.
However, any face mask is only as good as other health and hygiene practices. Experts universally agree that there’s simply no replacement for thorough, frequent hand-washing for preventing disease transmission.
Some think the masks may also help to ‘train’ people not to touch their faces, while others argue that the unfamiliar garment will just make people do it more, actually raising infection risks.
So what about cloth coverings? Although good quality evidence is lacking, some data suggest that cloth masks may be only marginally (15 per cent) less effective than surgical masks in blocking emission of particles, said Babak Javid, principal investigator at Cambridge University Hospitals wrote in the BMJ on April 9.
He pointed to a study led by Public Health England in 2013 which found wearing some kind of material over the face was fivefold more effective than not wearing masks for preventing a flu pandemic.
The study suggested that a homemade mask ‘should only be considered as a last resort to prevent droplet transmission from infected individuals, but it would be better than no protection’.