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)
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.