Wearing a surgical or homemade face covering can help reduce the spread of coronavirus, according to new research.
Seven types of face masks were put to the test by the University of Edinburgh, including surgical masks, respirators, lightweight and heavy-duty face shields, and homemade face coverings.
Measurements were taken from people wearing different types of face mask both standing and lying down, as well as from a manikin connected to a cough-simulating machine.
A special type of imaging was then used to enable scientists to detect the distance and direction travelled by the air that is expelled when someone coughs or breathes heavily.
The results showed that wearing a face mask or other covering over the mouth and nose can reduce the forward distance travelled by an exhaled breath by more than 90 per cent.
As the breath could contain small droplets of water, some of which may contain traces of the virus, experts have said wearing any type of face covering could be crucial in tackling Covid-19.
Dr Felicity Mehendale, a surgeon at the Centre for Global Health at the University of Edinburgh's Usher Institute, said: "It was reassuring to see the handmade mask worked just as well as the surgical mask to stop the wearer's breath flowing directly forwards.
"This suggests that some handmade masks can help to prevent the wearer from infecting the public."
However, the team of scientists at the university did warn that some masks can present different problems.
While surgical masks and the tested handmade masks were found to limit the forward flow of a breath, they also enabled strong jets of air to escape from the back and sides.
Only masks that formed a tight seal with the face were found to prevent the escape of virus-laden fluid particles, the team said.
Dr Ignazio Maria Viola, of the University of Edinburgh's School of Engineering, who co-ordinated the project, said: "I have generally been impressed by the effectiveness of all the face coverings we tested.
"However, we discovered that some face coverings allow the emergence of downward or backward jets that people are not aware of and that could be a major hazard to others around them."
Dr Mehendale added: "The strong backward jets mean you need to think twice before turning your head if you cough while wearing a mask and be careful if you stand behind or beside someone wearing a mask."
The University of Edinburgh says its findings could help steer official guidance on wearing masks to help tackle coronavirus.