The US government has changed its guidelines on covering one's face to prevent further spread of coronavirus.
President Trump said the new recommendations to wear a non-medical mask were "voluntary".
Wearing a mask in public has been recommended by public health bodies in several Asian countries such as China and South Korea.
But in many Western countries, members of the public have been told not to wear a mask unless they are sick.
The European Centre for Disease Prevention and Control even warns that masks can increase the "risk of infection due to a false sense of security", a sentiment that has been echoed by other international officials.
The US Surgeon General even tweeted in early March that Americans should stop buying masks.
Their stark change in position on the issue is based on information that people without symptoms could be unknowingly transmitting the virus.
Potentially one in four people with COVID-19 are asymptomatic, the US Centres for Disease Control and Prevention (CDC) director Robert Redfield told Atlanta's public radio station on Monday, although it was not immediately clear what data he was citing.
This means, Redfield said, that others can spread the virus before they develop symptoms. Those details prompted the US public health agency to review their guidelines on wearing face masks.
The previous CDC guidelines state that only those members of the public who are sick should wear masks, which is similar to the guidelines set in place by the World Health Organization (WHO) and European Centre for Disease Prevention and Control (ECDC).
Indeed very few European countries have ordered members of the public to wear masks - but some, notably, have.
Austrian chancellor Sebastian Kurz made it mandatory for members of the public to wear masks inside supermarkets, stating that he knew it would be a big cultural change for Austrians.
The Czech Republic's prime minister Andrej Babis recently tweeted to US President Donald Trump encouraging the use of masks: "Wearing a simple cloth mask, decreases the spread of the virus by 80 %! Czech Republic has made it OBLIGATORY for its citizens to wear a mask in the public," he wrote.
Experts have long argued in Western countries that there was little data to support wearing face masks to prevent the spread of viruses.
Germany's Robert Koch Institute has stood by their recommendation that hand-washing and social distancing are still the best measures to protect against the virus. Masks do not protect those that wear them and there is no evidence that they protect others, director Lothar Wieler has said.
They have also emphasised that there is a difference between surgical grade masks and other protective masks.
But Dr Harvey Fineberg, chair of a US National Academy of Sciences committee on infectious diseases advising the White House, wrote in an April 1 letter to the government, that there is some evidence to suggest that this coronavirus can spread just through exhalation or conversation, citing several recent studies.
Fineberg wrote that a recent University of Hong Kong study suggested that wearing a surgical mask could help prevent the spread of RNA viruses, such as SARS-CoV-2 which causes COVID-19.
Amidst a global mask shortage, US cities began suggesting people cover their faces in public with a homemade mask or scarf.
Indeed many countries are scrambling to provide healthcare workers with the necessary surgical grade face masks needed to protect healthcare workers. France and the UK notably have ordered millions of masks to protect health workers.
"The chronic global shortage of personal protective equipment is now one of the most urgent threats to our collective ability to save lives. We must provide the protection health care workers deserve to save our lives," a WHO spokesperson told Euronews.
But amidst the mounting discussion of masks and protection, WHO's director-general Dr Tedros Adhanom Ghebreyesus said on Wednesday that the body "continues to evaluate the potential use of masks more broadly to control COVID-19 transmission at the community level".
For the time being, they only recommend that those who know they are sick wear them to prevent spreading to others.