Since the start of the coronavirus outbreak, the official advice from the World Health Organization has been clear. Only two types of people should wear masks: those who are sick and show symptoms, and those who are caring for people who are suspected to have the coronavirus.
Nobody else needs to wear a mask, and there are several reasons for that.
One is that a mask is not seen as reliable protection, given that current research shows the virus is spread by droplets and contact with contaminated surfaces. So it could protect you, but only in certain situations such as when you're in close quarters with others where someone infected might sneeze or cough near your face. This is why experts say frequent hand washing with soap and water is far more effective.
Removing a mask requires special attention to avoid hand contamination, and it could also breed a false sense of security.
Yet in some parts of Asia everyone now wears a mask by default - it is seen as safer and more considerate.
In mainland China, Hong Kong, Japan, Thailand and Taiwan, the broad assumption is that anyone could be a carrier of the virus, even healthy people. So in the spirit of solidarity, you need to protect others from yourself.
Some of these governments are urging everyone to wear a mask, and in some parts of China you could even be arrested and punished for not wearing one.
Meanwhile, in Indonesia and the Philippines, where there are suspicions that there are many under-reported cases, most people in major cities have begun wearing masks to protect themselves from others.
For many of these countries, mask-wearing was a cultural norm even before the coronavirus outbreak. They've even become fashion statements - at one point Hello Kitty face masks were the rage in the street markets of Hong Kong.
In East Asia, many people are used to wearing masks when they are sick or when it's hayfever season, because it's considered impolite to be sneezing or coughing openly. The 2003 Sars virus outbreak, which affected several countries in the region, also drove home the importance of wearing masks, particularly in Hong Kong, where many died as a result of the virus.
So one key difference between these societies and Western ones, is that they have experienced contagion before - and the memories are still fresh and painful.
Meanwhile, in South East Asia, especially in more densely-populated cities, many wear masks on the streets simply because of pollution.
But it hasn't caught on everywhere in Asia - here in Singapore, the government has urged the public not to wear masks to ensure adequate supplies for healthcare workers, and most people walk around without one. There is substantial public trust in the government, so people are likely to listen to such advice.