Good Morning Britain viewers were issued a stark warning from Dr Hilary Jones 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.
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.
"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.
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.
