On Tuesday, Apr. 14, the government announced that it is now compulsory for everyone in Singapore to wear masks when they leave the house.

But nearly all the way till then, the directive from the government was that one should only wear a mask if one is unwell.

So how did we get to this point, and why have guidelines — which all of a sudden and very quickly turned into laws — surrounding masks changed so drastically?

We tracked Singapore's changing stances on masks in a timeline.

But first, let's get into this specific burning question: why are we wearing masks now?

1) New scientific evidence has emerged

The Ministry of Health (MOH) explained that the government's updated stance on mask-wearing follows new evidence from the World Health Organisation (WHO) that asymptomatic carriers of SARS-CoV-2 (the virus that causes Covid-19) may be infectious.

Current information, wrote the WHO, suggests that the two main ways Covid-19 is transmitted are through respiratory droplets and contact (close, within 1m, or through common surfaces or touch points).

But the data also showed that some people can test positive for Covid-19 one to three days before they develop symptoms, added the WHO.

This means that an infected person might not display symptoms, but their respiratory droplets are still infectious.

In light of these, the WHO made a U-turn on its stance on mask-wearing and now supports government initiatives that encourage its use in public.

"There may be situations where the wearing of masks may reduce the rate at which infected individuals may infect others," said Michael Ryan, executive director of the WHO’s health emergencies programme.

"We will support governments who wish to have a measured approach to the use of masks and who include that as part of the comprehensive strategy to control this disease."

So how do masks help? What's the science behind this?

Masks prevent droplets from flying too far away — or arguably, at all — when a person sneezes or coughs.

A group of Agency for Science, Technology and Research (A*STAR) scientists, in collaboration with SingHealth doctors from the SGH Department of Infectious Diseases and the Department of Respiratory and Critical Care Medicine conducted an experiment showing the importance of wearing a mask.

They explain:

"When a person coughs or sneezes, he releases a cloud of droplets into the air. Within seconds, the heavier particles will drop to the ground.

Lighter and smaller particles linger on for a while and do not fall immediately to the ground. Those around him may then be exposed to the droplets.

However, when one wears a mask properly, fewer or no droplets are released into the atmosphere when one coughs or sneezes."

Using a high-sensitivity camera, the experiment they conducted compared the amount of droplets released when a person coughs

• without a mask,
• with a mask, and
• with a mask improperly worn.

Without a mask, respiratory droplets, some as small as one-tenth the width of a hair, can travel up to two to three metres away.

Wearing a mask properly, however, can block a significant number of droplets and aerosols from a person's nose and mouth, the video explained.

Thus, very few droplets enter the air.

The experiment then showed what happens when a person wears a mask improperly, without covering their nose.

The mask was still able to stop most of the droplets, but a small number still made their way out, and can potentially infect someone.

You can watch the full video summarising the experiment here.

Now that we understand why masks are important in our current situation, let's get to why the guidance on their usage has changed over time.

Starting with —

Jan. 2020: 'Wear a mask only if you are unwell'

Even prior to Singapore's first confirmed Covid-19 case being announced on Jan. 23, Singaporeans were actively buying up available stocks of masks in stores.

On Jan. 22, N95 masks were sold out at multiple pharmacy outlets and on several online shops in Singapore.

The government reminded the public not to panic and to only wear masks if they were unwell.

Senior Minister of State for Health Lam Pin Min posted on Facebook on Jan. 28, reassuring Singaporeans that there is a sufficient supply of masks in Singapore "if we use them sensibly and responsibly".

"There is no need to rush to buy masks. We are working with retailers like NTUC FairPrice and Unity Pharmacy to push out the stocks."

In a similar Facebook post on Jan. 28, NTUC FairPrice CEO and Marine Parade GRC Member of Parliament (MP) Seah Kian Peng urged people not to hoard masks:

"Please do not hoard or buy more than what we need. Again, we only need to put the mask on if we are unwell."

Prime Minister Lee Hsien Loong also took to Facebook on the same day with a statement on the progressing virus situation.

On the issues of hygiene and mask usage, he wrote:

"All of us can do our part to limit transmission of germs by practising good hygiene. Wash your hands regularly, and seek medical advice early and wear a mask if you feel unwell.

But in general, there is no need to wear a mask if you are not ill."

By that day, there were seven confirmed cases of Covid-19 in Singapore, all of whom were Chinese nationals from Hubei province. There was no local transmission nor community spread.

Feb. 2020: Govt distributes 4 surgical masks to all households in the face of widespread mask panic-buying

Then, on Jan. 30, the government announced that it would be distributing 5.2 million masks to 1.37 million Singapore households, starting Feb. 1.

Each household would receive four.

The government also revealed that they had released 5 million masks to retailers in the previous nine days and still had more than enough stock left.

However, co-chair of the Multi-Ministry Taskforce Lawrence Wong said that the rate of Singapore's mask consumption was unsustainable even though the government was at that time sourcing for new mask suppliers and had ramped up purchases from traditional ones.

The taskforce also emphasised that masks were for those who are unwell, in order to prevent them from passing the virus to others. Those who were well did not need to wear masks, they reiterated.

They went big on these messages too — printed clearly on the masks that were distributed to households:

As well as, for a few weeks, on prominent advertisement bands like this one:

On February 11, four senior medical practitioners sent out a signed letter urging people in Singapore to proactively wear masks outside and stop unnecessary mingling with others, in view of the escalating situation.

The doctors also recommended that schools conduct online learning, people should minimise time in air-conditioned locations, as well as to avoid malls and food courts.

But at this juncture, it's worth pointing out something most of you likely already know:

March 2020: MOH reviews stance on masks

March saw a rise in the number of imported Covid-19 cases to Singapore. At its peak, the Ministry of Health reported 48 imported cases in a single day (Mar. 23).

On Mar. 31, MOH's Director of Medical Services Kenneth Mak shared that the ministry was in the process of reviewing available medical literature and evidence to inform its stance on face masks.

At that point, he was asked about whether people in Singapore should be wearing masks more, given that more doctors, particularly those overseas, were advising that wearing masks have helped to keep the number of cases of Covid-19 down.

"We continue to review the measures that we take and recommendations on a data-driven basis. We look at the evidence very carefully.

And this applies not just to masks but also to the rest — safety distancing measures that we undertake. As far as masks are concerned, we are, in fact, in the process of continuing to review the data that's available both in the literature and the evidence, as well as international experience.

And when we have completed this current round of review, we'll make those recommendations available. This includes our recommendations for masks policies."

This came soon after Gao Fu, director of the Chinese Centre for Disease Control (CDC), reportedly said that people were making a mistake by not wearing masks in public in the United States and Europe.

This was contrary to the WHO's advice on mask-wearing at the time, which continued to state that a person only needs to wear a mask if they are coughing or sneezing, or if they are taking care of a person suspected to have Covid-19.

Early April 2020: PM Lee says govt no longer discourages mask use

By April, the number of community cases reported here moved into a steep upward trajectory.

In his address to the nation on Apr. 3, his third on the Covid-19 situation, PM Lee announced that the government would be putting in place a Circuit Breaker from Apr. 7 to May 4 to try to stem the spike in local Covid-19 cases.

Most workplaces and all schools would be shut down.

Aside from implementing the Circuit Breaker, PM Lee said, the government was "rethinking" its advice on masks, and would no longer be discouraging people from wearing them in public.

He acknowledged that the government had initially advised only those who were unwell to wear masks, explaining that its initial guidance had been based on scientific advice and guidelines from the WHO.

Also, he said, at those earlier stages, Singapore had not yet seen significant spread of Covid-19 in the community, which made it unlikely for people to run into an infected person on the street.

PM Lee added that both the WHO and the U.S. Centers for Disease Control and Protection were reviewing their advice on face masks as well since there was evidence that showed that a person could display no symptoms of the virus, yet still pass it on to others.

Given these developments, he said, the government was also of the view that there could be a few undetected cases in the community.

Thus, PM Lee said, wearing a mask could protect others in the event that one has the virus but does not know it:

"This is so that you keep your droplets to yourself. It can also protect yourself a little better, especially if you are elderly, or vulnerable because of pre-existing conditions."

In the meantime, he said, reusable masks would be distributed to all households, starting Sunday, Apr. 5.

One day after Singapore's circuit breaker measures kicked in, on Apr. 8, PM Lee posted a photograph of the Cabinet ministers in a meeting room, all wearing masks and practicing social distancing.

PM Lee explained that, despite the circuit breaker measures, the Cabinet still had to meet.

He elaborated that they were teleconferencing between two locations, spaced out to maintain safe distancing, and wearing masks to "keep our droplets to ourselves".

He reminded Singaporeans to stay home, except to go out to do essential work or buy food, writing:

"This is not a month long holiday, when we can go out for jalan jalan or to meet up with friends.

The health of us all depends on the actions of each of us. Please do your part."

Mid-April: Masks must be worn in certain places

On Apr. 11, it was announced by multiple government agencies that masks have to be worn at a variety of locations.

The National Environment Agency (NEA) said that from Apr. 12 onwards, people not wearing face masks would not be allowed to enter the 40 markets managed by them or NEA-appointed operators.

This was because of the "generally crowded and closed-in environment in markets", said the agency.

NEA said the move was to safeguard the well-being of all stallholders and patrons at the markets, which tend to attract crowds over the weekends.

This also followed Minister Lawrence Wong saying on Apr. 9 that wet markets had become "hotspots that we really need to manage".

Also on Apr. 11, Enterprise Singapore (ESG) and the Singapore Tourism Board (STB) announced that from Apr. 12, it would be compulsory for people to wear masks in supermarkets, convenience stores, pharmacies, and shopping malls.

ESG and STB also said that the aforementioned venues had the right to turn away those who do not wear masks, similarly to protect the health and well-being of customers and staff in these premises.

Minister for Transport Khaw Boon Wan also announced that the government would be making it mandatory for all commuters to wear masks on public transportation, even after the Circuit Breaker period ends.

He explained that once crowds return to trains and buses and safe distancing is not possible, wearing masks would help minimise transmission of the virus on public transport.

2 days later: Mask-wearing compulsory outside, for everyone.

And as we all know by now, the government announced on Apr. 14 that it was further changing its guidance on masks, making it mandatory for everyone to wear masks when they go out of the house, effective immediately.

There are two exceptions to this rule:

1. Children under the age of two will not have to wear one, at the recommendation of medical experts.
2. Those who are engaging in strenuous exercise, such as running or jogging, may also remove their masks temporarily. However, they must put it back on once they have completed their exercise.

"Other than these exceptions, everyone else going out will have to wear a mask, and we will enforce this rule too, like all the other safe distancing and circuit breaker measures that we have put in place," said Minister Wong.

Minister for Health Gan Kim Yong added that this measure may "well continue" after the Circuit Breaker period ends, and will be reviewed.

As of 12pm on Apr. 15, MOH has confirmed 3,699 cases of Covid-19, with 447 new cases announced that day — all locally-transmitted.

So as the number of locally-transmitted as well as unlinked cases in Singapore continues to go up, we all need to play our part in staying safe and responsible by staying at home and wearing a mask when we go out.

Mothership Explains is a series where we dig deep into the important, interesting, and confusing going-ons in our world and try to, well, explain them.

This series aims to provide in-depth, easy-to-understand explanations to keep our readers up to date on not just what is going on in the world, but also the "why's".

Top photos courtesy of Merrill Tang and via Suhaimi Abdullah/Getty Images.