The UK public may soon be advised to wear face coverings or scarves to protect themselves against coronavirus - but how effective is this?
Scientific advisors to the government are expected to announce in the coming days that the public should not use medical grade face masks to prevent viral transmission, but that they should use face coverings or scarves instead.
Medical grade masks will be prioritised for health workers in the NHS, who need them more than the public.
In some countries around the world, such as the US, face masks are now compulsory in public. In Germany, they have to be worn on public transport. Residents in the hard-hit Lombardy region of Italy must cover their nose and mouth while out in public.
However, there has been fierce debate among experts regarding the effectiveness of masks (especially homemade ones) in the fight against coronavirus.
The case for masks
The World Heath Organisation (WHO) only recommends masks for two groups of people:
- Those who are already unwell and showing symptoms- Those who are caring for people who are suspected to have coronavirus
However, the advice on masks varies between organisations and countries, with The European Centre for Disease Prevention and Control saying non-medical face masks may help prevent viral transmission by people who are asymptomatic.
Masks can offer protection from water droplets transmitted from coughs or sneezes. However, most experts agree that masks are more effective in protecting sick people from transmitting disease than they are at preventing healthy people from getting it.
Paul Hunter at the University of East Anglia and his colleagues looked at 31 published studies on the effectiveness of face masks. The New Scientist reports that their results suggested there may be some small benefit to wearing a kind of mask or face covering - mostly by preventing unwell people from transmitting the virus.
However, Hunter told the magazine that the evidence for this remains inconsistent and weak.
“Our view is that there was some evidence of a degree of protection, but it wasn’t great,” he told the New Scientist," he said.
“So we still don’t effectively know if face masks in the community work.”
Hunter said that there was enough evidence to support the wearing of masks by frontline staff - such as supermarket workers - and vulnerable people entering high-risk environments, as long as this didn't take supplies away from healthcare workers.
The effectiveness of a mask also depends on how well it is made, what it is made of and how it is fitted, with some droplets small enough to get through certain masks or coverings.
The case against masks
Where governments or organisations have mandated that the public wear face masks in public, these measures have also been accompanied by strict physical distancing. This is one of the reasons why it has been difficult to tell how effective face coverings and masks really are in the community.
Some experts are also concerned that poorly-fitted or made masks could actually increase the risk of picking up coronavirus.
Martin Marshall, chair of the Royal College of General Practitioners, told BBC Radio 4’s Today programme that no research supported wearing a mask if you were fit and well, and that there may be a risk of picking up infection if wearers were constantly touching their face to adjust it.
There is also some concern that reusable cloth masks may increase the chance of infection. European advisors say that there is a high chance virus particles could go through cloth, and the moisture in it could retain the virus.
Can a scarf or a face covering protect me in public?
Overall, most experts agree that there is varying evidence regarding the effectiveness of homemade masks or face coverings against coronavirus, with more rigorous research needed.
While some say that a homemade mask is better than nothing, others say there is not enough evidence even to suggest this.
Broadly, existing research has shown that homemade coverings are much less effective at protecting against viruses than medical-grade masks.
If you do decide to wear a mask - homemade or not - it is important that you do not let it lull you in to a false sense of security.
Almost all experts and organisations agree that wearing a mask of any kind is not a replacement for the recommended prevention techniques of physical distancing, frequent hand washing and avoiding touching your face with unclean hands. WHO says that masks are most effective when used in combination with these hygiene practices.
"[Using respiratory coverings] in itself is not a bad idea, but that doesn't negate the need for hand washing. It doesn't negate the need for physical distancing," Dr Michael Ryan (executive director of the World Health Organization Health Emergencies Programme) told a press conference on 3 April.
"It doesn't negate the need for everyone to protect themselves and try to protect others."