Why masks work: People are exposed to 10,000 TIMES more cough droplets from a mask-less patient two metres away than from someone wearing a covering standing just 50cm away
- Droplets expelled by the mouth and nose are the main way Covid-19 can spread
- Scientists conducted experiments with real people and mannequins
- They compared droplet levels on surfaces with and without the use of masks
- ‘Not a single droplet’ was omitted by the participants wearing a face mask
Coughing or sneezing without a face covering exposes bystanders to at least 10,000 times more droplets, scientists claim.
Droplets — large particles that fall to the ground and land on surfaces — are thought to be the main driver of Covid-19 transmission.
Academics ran a number of experiments with real people and life-sized mannequins connected to a machine that simulates coughs and speech.
They compared the number of droplets that landed on a surface in front of a person coughing and speaking with and without a mask or basic covering.
The findings suggest a person standing two metres from someone coughing without a mask is exposed to 10,000 times more droplets than from someone standing half a metre away wearing a basic single layer mask.
‘Not a single droplet’ was emitted by volunteers wearing a surgical mask, according to the researchers. They said even a simple cotton mask is ‘tremendously effective’.
The science supporting wearing masks to protect against Covid-19 has been weak so far. But several studies have recently emerged to support their use.
Coughing or sneezing without a mask exposes bystanders to 10,000 times more droplets, a study has found, supporting their use during the Covid-19 pandemic. Pictured: A shopper wearing a mask in Sheffield, south Yorkshire, on July 24
In human studies, ‘not a single droplet’ was omitted by the participants wearing a surgical face mask, the study claimed. The two graphs show how many droplets were emitted by participants when talking (left) and coughing (right) when wearing a mask
In the first experiment using mannequins, air containing a fluorescent liquid to represent the droplets was ejected from the mouth. Pictured: Examples of images captured directly in front of the mouth for speaking (upper row) and coughing (lower row), without a mask (1st column), with the handmade mask (2nd column) and with the surgical mask (3rd column)
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’.
Lead researcher Dr Ignazio Maria Viola, of the University of Edinburgh, said: ‘We knew face masks of various materials are effective to a different extent in filtering small droplets.
‘However, when we looked specifically at those larger droplets that are thought to be the most dangerous we discovered that even the simplest handmade single-layer cotton mask is tremendously effective.
‘Therefore, wearing a face mask can really make a difference.’
Scientists at the university compared the number of droplets that landed on a surface in front of a person coughing and speaking.
In the first experiment using mannequins, air containing a fluorescent liquid to represent the droplets was ejected from the mouth.
The team quantified the number of droplets travelling through air using laser illumination and UV-light.
They also assessed how many droplets landed at table height up to two metres away.
Although they tried to make it as similar to real life as possible, studies on objects are not as useful as using real people, the team admitted.
In the second experiment, six volunteers were tasked with coughing and talking for several minutes with and without a surgical mask.
Their droplets were caught on a slide placed five centimeters from the mouth and analysed under the microscope.
In both the mannequin and human studies, masks decreased the number of projected droplets by more than 1,000-fold.
A cough can travel as fast as 50 mph and expel almost 3,000 droplets in just one go on average, experts say. But sneezes can give off up to 100,000 particles.
The researchers estimated that a person standing two metres from someone coughing without a mask is exposed to over 10,000 times more respiratory droplets than from someone standing half a metre away wearing a basic single layer mask.
When the mannequin wore any of the two face masks, less than one in 1,000 particles escaped into the environment.
In contrast to the mannequin tests, there was a large variability in the number of droplets expelled by the people without a mask.
‘However, for all subjects, we did not find a single droplet when a mask was worn,’ the paper said.
‘Between 10s and 1000s’ of particles were measured for speaking and coughing without a mask, but “zero particles” were seen when using a surgical mask, the scientists claimed.
Professor Paul Digard, of the University of Edinburgh’s Roslin Institute, said: ‘The simple message from our research is that face masks work.
‘Wearing a face covering will reduce the probability that someone unknowingly infected with the virus will pass it on.’
According to the scientists, their results contrast with previous research that suggested masks are less effective.
However, those studies also measured smaller droplets — known as aerosols — which can remain airborne for hours and don’t immediately fall.
It is still unclear if aerosol transmission of Covid-19 is a main transmission route, and therefore a study for large droplets is useful.
The team cautioned that if aerosol transmission is found to be significant, then it changes the results of their findings.
Their results may overestimate the effectiveness of masks and coverings, which will not necessarily protect against aerosol transmission.
Nevertheless, for bigger droplets, masks are extremely effective in reducing spread to the immediate surroundings, researchers said.
The researchers added their findings, which are presented in a preprint paper and not in a medical journal, could have implications for social distancing measures.
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