Face masks have become a common sight in supermarkets and on the streets in recent weeks, with many people choosing to cover their mouth and nose with homemade or items bought online.

But do they help stop the spread of Covid-19 and should people be wearing them?

What is the UK Government’s advice?

Public Health England (PHE) has emphasised the importance of masks for doctors and nurses but has not suggested widespread public usage.

However on Monday, Sir Patrick Vallance, the Government’s chief scientific adviser, said the UK position on masks was under review and would change if the scientific evidence warranted it.

What does the World Health Organisation (WHO) say about masks?

The WHO has recommended that outside of healthcare professionals, people should only wear masks if they display symptoms of Covid-19 or are taking care of someone who does.

But it also emphasised a mask on its own is not enough to protect people from the virus and other preventative measures such as hand washing should also be used.

However, Dr David Nabarro, the organisation’s special envoy for Covid-19, has said people would need to become accustomed to a “new reality” where masks are common in the wake of the pandemic.

He told the BBC: “Some form of facial protection, I’m sure, is going to become the norm, not least to give people reassurance.

“But, I would say, don’t imagine that you can do what you like when you are wearing a mask.”

Are there any downsides to wearing facemasks?

At present there is no robust scientific evidence to suggest ordinary masks can stop the virus from infecting people who wear them.

Filtering face piece masks, both FFP2 and FFP3, recommended as PPE for doctors and nurses who are treating people with Covid-19, do offer protection, but the virus particles are thought to pass through other types of masks.

More common in public are surgical masks, which are more loose-fitting but can be a means of preventing the spread of droplets released by someone coughing or sneezing, according to the European Centre for Disease Prevention and Control (ECDC).

The WHO has also suggested widespread use of masks could lead to a false sense of security and cause people to neglect other essential hygiene and distancing measures.

Can you make your own?

While many people are opting to make masks at home using cloth or other materials, researchers from the ECDC have suggested these may not be effective and up to 90% of particles can make their way through the fabric.

The EU agency says there is no evidence that non-medical face masks or other face covers provide effective protection for the wearer of the mask and have been shown to have “very low” filter efficiency.

What does the latest research say on benefits of face masks?

While there is no conclusive evidence to suggest wearing a face mask could stop people from catching the virus, it is accepted that they can block the transmission to other people.

A study published in Nature Medicine in early April suggested surgical masks could help prevent infected people from making others sick with seasonal viruses, including coronaviruses.

In addition, Jeremy Howard, a University of San Francisco research scientist and founder of the #Masks4All campaign, led a review panel with 18 other experts from around the globe and found “substantial evidence in favour of widespread mask use to reduce community transmission”.

Mr Howard cited the WHO’s assistant director-general David Heymann’s comment that masks were equally or more effective in combating the spread of Covid-19 than social distancing, and said the situation in Taiwan provided further proof.

He told ITV’s Peston programme: “Regardless of how you look at it, it looks like there’s an extra 1,500 deaths a week (in the UK) due to this disease.

“The entire country of Taiwan has five deaths. Now here’s an example of a great country that is distributing masks to everybody.”

What are other countries doing?

People living in the US are being told to wear cloth face masks when they go out.

The Centre for Disease Control (CDC) now recommends “wearing cloth face coverings in public settings where other social distancing measures are difficult to maintain”.

It said these rules apply “especially in areas of significant community-based transmission” such as New York City.

In China, Hong Kong, Japan, South Korea, Thailand and Taiwan, the wide assumption is that anyone could be a carrier of the virus, so the advice is for everyone to wear a mask.

How easy is it to buy masks?

There are many different types of face masks available online, including through sites such as Amazon and eBay, although a surge in demand has made it harder to get hold of the items and forced prices up.