SINGAPORE - Wearing a mask is not the most important thing to do to keep the coronavirus at bay, said Associate Professor Kenneth Mak, director of medical services at the Ministry of Health (MOH).

He was responding to questions on the advice circulated by four doctors that everyone should wear a mask when leaving home, regularly wash hands and reduce unnecessary mingling with others - challenging official advice, which is to wear a mask only if sick.

They argued: "If one faces a person and both parties are masked, it is considerably safer, constituting a two-barrier protection."

Asked about this at a press conference on Wednesday (Feb 12), Prof Mak noted that there has been a lot of well-intentioned advice circulated on social media, including from doctors.

Referring to the letter, Prof Mak said that while some advice is very relevant, such as reminders to wash your hands, people must remember that the virus is spread via droplets, with no evidence that it is airborne.

"And be aware of things you commonly touch. The thing most commonly touched is your phone, so wearing a mask is not the most important thing," he said.

Government leaders have been saying that only those who are unwell need to wear a mask, while those who are well need not do so. In fact, as the virus is spread by droplets, keeping hands clean and away from the face are more important ways to avoid catching the bug.

One of the signatories to the letter, Dr Colleen Thomas, an internal medicine specialist in private practice, told The Straits Times that she knows the advice goes against what the MOH has been saying - that only those who are sick should wear masks and those who are well should not, as masks don't give full protection against the virus and may give a false sense of security.

Still, she said the four doctors felt obliged to send out the warning "because the burden of not doing so is too great to bear".

Dr Thomas also said one of her colleagues had contracted Sars (severe acute respiratory syndrome) while unknowingly treating a patient. He then passed the virus to his mother, who later died of it.

Their letter, which is spreading within the community and in chat groups, said: "The infected are not always traceable and containable within hospital isolation rooms."

"As this virus is said to be milder, infected people with no symptoms could transmit the virus to others silently."

Their advice is any mask is better protection than no mask.

Dr Thomas said: "As a doctor, how can I not speak out when I know that there is danger to people?"

These doctors' advice includes winding down windows in taxis, spending less time in air-conditioned places, like shopping malls and food courts, and for schools to conduct online learning.

The letter, written on Monday and sent out on Tuesday, concluded that if everyone wears masks and reduce mingling, "in two weeks, the worst could be over".

But Associate Professor Hsu Li Yang of the NUS Saw Swee Hock School of Public Health said: "It is highly unlikely that such measures will result in the worst being over in two weeks.

"Social distancing is a sound strategy to reduce the transmission of respiratory viruses," he added. "There is little evidence to show that wearing surgical or N95 masks in the community when well will protect the individual, much less home-made masks or scarves.

"They may instil a false sense of confidence, and deplete mask supplies unnecessarily."

Correction note: An earlier version of the article said Dr Colleen Thomas was infected with Sars during the 2003 outbreak. She has clarified that she was not infected.