Dr Hilary Jones issued a stark warning on why wearing a face covering is so important during the coronavirus pandemic.
New research suggests wearing a face covering lowers the risk of spreading Covid-19 to others through speaking and coughing.
Speaking and coughing without face protection exposes people nearby to droplets carrying the virus that could otherwise be stopped by wearing a mask, according to the study.
Recognising the importance of these new findings, Dr Hilary urged Good Morning Britain viewers to wear a mask to reduce the risk.
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He said: "Just being outside is not an absolute protector and interestingly some research coming out has shown that if someone is coughing wearing a mask there is ten thousand times less droplet transmission to two metre away.
"It's actually safer to be 0.5m away of someone wearing a mask than 2m away if they're not wearing a mask.
"So it kind of adds to the research that masks are important."
Lead researcher Dr Ignazio Maria Viola, of the University of Edinburgh's School of Engineering, said: "We knew face masks of various materials are effective to a different extent in filtering small droplets.
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"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 without and with a surgical mask or a basic cotton face covering.
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Tests were carried out on people and a life-sized anatomical human model connected to a machine that simulates coughs and speech.
Analysis found that the number of droplets was more than 1,000 times lower when wearing even a single layer cotton mask, the researchers say.
They add that the findings, published on a non-peer reviewed preprint server, could have implications for social distancing measures.
