Masks can block 99.9% of Covid-linked droplets, study shows

During the experiment, a life-sized anatomical human model was connected to a machine that simulates coughs and speech. A green laser sheet illuminated the in-flight droplets ejected by the manikin.
During the experiment, a life-sized anatomical human model was connected to a machine that simulates coughs and speech. A green laser sheet illuminated the in-flight droplets ejected by the manikin.
People who wear a face mask significantly lower the risk of spreading Covid-19 to others through speaking and coughing, research led by the School of Engineering suggests.

Speaking and coughing without face protection exposes people nearby to virus-laden droplets that would otherwise be stopped by wearing a mask, the study shows. 

Someone standing two metres from a coughing person who has no mask is exposed to 10,000 times more droplets than someone merely half a metre from a coughing person who is wearing one, the researchers found. 

The findings – which have now been published in the Royal Society’s Covid-19 Publishing Collection [updated 23 December 2020]  – could have implications for social distancing measures, the team says. 

Researchers compared the number of droplets that landed on a surface in front of a person coughing and speaking without and with a surgical mask or a basic cotton face covering. 

Tests were carried out on people and a life-sized anatomical human model connected to a machine that simulates coughs and speech. The analysis found that the number of droplets was more than 1,000 times lower when wearing even a single layer cotton mask. 

These results contrast with previous studies which have found masks to be less effective, but these studies also measured small droplets, known as aerosols, which can remain airborne for hours. 

It is still uncertain how much virus transmission occurs by aerosol, but if this does turn out to be significant, the current findings overestimate the protective effects of face coverings, the team says. 

Nevertheless, for bigger droplets carrying the largest amount of virus masks are very effective indeed in reducing spread to the immediate surroundings. 

The study was funded by the Engineering and Physical Sciences Research Council, the Biotechnology and Biological Sciences Research Council, the European Commission and Japan Student Services Organization. 

Lead researcher Dr Ignazio Maria Viola, who is Reader in the School’s Institute for Energy Systems, 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.” 

Fellow researcher 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.” 

Dame Ottoline Leyser, Chief Executive, UK Research and Innovation (UKRI), said: “The Covid-19 pandemic is a crisis that has impacted virtually everybody. In these extraordinary circumstances we have seen the value of rapid and collaborative research in supporting our response to the crisis. The findings published today from a study led by researchers at the University of Edinburgh and co-funded by UKRI support the growing body of evidence that face coverings reduce Covid-19 transmission via respiratory droplets. 

“Research into Covid-19 is obviously a relatively new field, with the science still evolving. New information about the virus plays a crucial role in informing policy makers and the public.”

This study builds on the team’s previous research on the aerodynamics of Covid-19 (linked below), which generated about 500 news articles and 100 broadcast clips, with an estimated total reach of over 4 billion people.   

Read the team's studies