Wearing face coverings could reduce the spread of Covid-19, according to a new study by the University of Edinburgh.
Research has found wearing a face covering can reduce the forward distance of an exhaled breath by more than 90%.
As the breath could contain small droplets of water, some of which may contain traces of the virus, experts have said covering up the mouth and nose could help combat Covid-19.
Scientists testing the effectiveness of seven different types of face coverings, including medical grade and home made masks, said they could all potentially limit the spread of coronavirus.
The Scottish Government advised people on April 28 to wear face masks while out of the home, with the UK Government making the recommendation on May 11.
Neither have made the policy mandatory.
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."
But a team lead by engineers at the university found some masks enabled strong jets of air to escape from the back and sides.
Surgical masks and the tested handmade masks were found to limit the forward flow of a breath out but also generate far-reaching leakage jets to the side, behind, above and below.
Heavy breathing and coughing, in particular, were shown to generate intense backward jets.
Only masks that form 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."