Shoppers in England will have to don masks or face coverings in stores and supermarkets within weeks.
Face coverings are already being used in public spaces including on transport and shops in many countries.
it comes as scientists warn of mounting evidence Covid-19 spreads through the air as well as by droplets settling on surfaces.
Police in England will get powers to fine shoppers who refuse to cover their faces up to £100 each.
The move has been welcomed by retailers and leaders after days of mixed-messaging from the government.
But many have slammed Prime Minister Boris Johnson over delays in following other countries in bringing in the measure to halt the spread of deadly coronavirus.
England’s new rule doesn’t kick in until July 24, as the government says it is giving shoppers and retailers time to prepare for the change.
Here’s why it’s important to follow the rules…
How do face masks and coverings stop the virus?
A key symptom of deadly coronavirus is a telltale persistent cough.
But worryingly, the world now knows some people suffer no symptoms at all yet can continue to spread the killer virus.
A growing chorus of scientists are recommending face coverings in hopes they will be a barrier to the asymptomatic spreading of Covid-19.
Concerns over the virus’ transmission has led some countries to make wearing the coverings compulsory.
Although others have allowed the public to decide if they want to wear one – including much of the UK up until England’s latest rule-change.
While experts had warned the virus can be caught from surfaces touched or coughed on by infected people, researchers are also warning it may be airborne.
One scientist highlighted how easy it could be to spread the virus with a grim experiment.
In simple science experiments, Dr Rich Davies, Clinical Microbiology Lab Director at Providence Sacred Heart, shared how face coverings could prevent illness spreading.
On Twitter, he wrote: “What does a mask do? Blocks respiratory droplets coming from your mouth and throat.”
In the first experiment, Dr Davies sneezed, sang, talked and coughed towards an agar culture plate both with and without a mask.
The results revealed that wearing a mask stopped almost all respiratory droplets from reaching the agar plate.
However, the plates used in the tests without a mask were covered in bacteria colonies.
In the second experiment, Dr Davies tested how far respiratory droplets could travel both with and without a mask.
He wrote: “I set open bacteria culture plates 2, 4 and 6 feet away and coughed (hard) for ~15s. I repeated this without a mask.
“As seen by number of bacteria colonies, droplets mostly landed <6 ft, but a mask blocked nearly all of them.”
Dr Davies said it was not a proper scientific test to model the spread of the Covid-19 virus. He was also measuring the travel of bacteria, not viral particles.
But he added: “But colonies of normal bacteria from my mouth/throat show the spread of large respiratory droplets, like the kind we think mostly spread #COVID19, and how a mask can block them!”
Masks could stop airborne spread
More leading health bodies have been shifting their position on face coverings in recent months, after earlier declaring masks of limited use in halting the virus’ spread.
The World Health Organisation (WHO), notably issued a report saying “aerosol” transmission “cannot be ruled out”.
It said much more research is needed, but said airborne transmission could explain how some cases had spread in crowded and inadequately ventilated spaces.
The report described how experiments using high-powered jets had found the virus particles remained airborne for three hours in one study and 16 hours in another.
However it clarified the experiment conditions did not reflect typical human coughing.
Prof Wendy Barclay, Head of the Department of Infectious Disease at Imperial College London and a SAGE member, said ahead of the new face covering rule announcement that the WHO’s report was significant.
She told the BBC’s Andrew Marr show: “What this new acknowledgement means is the route through the air probably also contributes in some circumstances.”
Prof Barclay said people could slow the spread by being in a well-ventilated room, social distancing – and wearing a face covering.
She explained how it is “quite likely” that a face covering will remove “some of” the droplets from your breath.
“We do think this virus is breathed out in droplets,” she said.
“Whether or not those droplets are large or small, it’s quite likely that a face mask will remove some of them from your breath.”
The virus could also likely spreading without coughing, the expert said.
Loud talking, singing or exercise may increase the risk of transmission, she explained: “There have been a number of outbreaks associated with choirs for example.”
And a new study claims that wearing a face mask can reduce your risk of being infected with coronavirus by 65%.
Researchers from the University of California Davis Children’s Hospital say the findings highlight that ” masks work and are very important “.
Face masks have become a politicised issue in the United States, where some including state leaders are refusing to wear them in public spaces.
The study last week underlined the importance of wearing wearing a face covering – finding it could nearly halve an infected person’s risk of transmitting the virus.
Dean Blumberg, chief of pediatric infectious diseases at UC Davis Children’s Hospital, said refusing to believe wearing a mask could stop the virus was like “not believing in gravity”.
He said: “We don’t know who might spread it. We do know social distancing reduces the risk of transmitting the virus by 90%, and wearing masks decreases the risk by 65%.”
“Everyone should wear a mask. People who say ‘I don’t believe masks work’ are ignoring scientific evidence. It’s not a belief system. It’s like saying, ‘I don’t believe in gravity.’”
He added: “People who don’t wear a mask increase the risk of transmission to everyone, not just the people they come into contact with.
“It’s all the people those people will have contact with. You’re being an irresponsible member of the community if you’re not wearing a mask. It’s like double dipping in the guacamole. You’re not being nice to others.”
What are the new rules?
People in England have had to wear face coverings on public transport since May, including on trains, buses, coaches, ferries, trams and aircraft.
From July 24 that rule will apply to shops in England too.
Some people are exempt from wearing coverings on transport and in shops.
They include children aged under 11, people with disabilities or breathing difficulties, anyone travelling with someone who relies on lip-reading.
It is also permitted to remove the face covering temporarily where “reasonably necessary” in order to eat or drink.