SINGAPORE - What constitutes a face mask in the time of Covid-19?
This question was raised after a recent incident where a bus driver refused to allow a man wearing a neck gaiter to board because the driver felt it was not a mask.
Under Singapore regulations, a mask refers to "any paper or textile covering designed or made to be worn over the nose and mouth to provide the wearer protection against infections or air pollution, but excludes a face shield".
But a study by Duke University in the United States published in Science Advances journal this month found that there are "masks" that actually increase the spread of droplets, rather than reduce it.
While most people would abide by the spirit of the law and wear proper masks, a minority in all societies will try to flout the law.
The rule here - that everyone must wear a mask when they are out, unless they are exercising, eating or drinking - is open to interpretation on what this mask should be.
A silk scarf covering the nose and mouth would offer some protection, but would it give enough?
Would the wearing of mask, as Covid-19 fatigue sets in, become more of a fashion statement rather than a health requirement for some?
Mask wearing is compulsory - with a $300 penalty for not doing so - because there are people with Covid-19 who do not fall sick, show no symptoms, and yet can infect others.
If everyone were to wear a mask when out, it would reduce the spread of droplets from such asymptomatic carriers, and cut the risk of the virus spreading to others unknowingly.
But not all masks are created equal. Some offer a greater barrier against the spread of the virus than others, although none are 100 per cent effective.
The rule of thumb is: The easier it is to breathe with the mask on, the less effective it is.
So people need to compromise between effectiveness and comfort.
The Duke study, which compared the spread of droplets from a range of masks, found that most of them gave fairly good protection.
However, the results of the study also found that one of the 15 types tested proved to be worse than not wearing a mask at all.
This was a single layer neck gaiter made of 92 per cent polyester and 8 per cent spandex.
Explaining this apparent anomaly, the researchers said the neck gaiter "seemed to disperse the largest droplets into a multitude of smaller droplets which explains the apparent increase in droplet count relative to no mask in that case".
"Considering that smaller particles are airborne longer than large droplets (larger droplets sink faster), the use of such a mask might be counterproductive."
The authors added that of the masks they tested, "some mask types approach the performance of standard surgical masks, while some mask alternatives, such as neck fleece (gaiters) or bandanas, offer very little protection".
Associate Professor Eric Westman, one of the researchers involved, in a webinar on the results said that the findings also showed "people do spit out particles when they speak", and not just when they cough, sneeze or shout.
Another mask that is better not worn in public spaces, and in fact has been banned in some places, are those with valves or vents.
Such masks, which make breathing easier, do protect the wearer. But they allow air, including any droplets in them, to freely flow out - and so, do not stop the transmission of the virus from an infected person.
Earlier this month, the US Centres for Disease Control and Prevention said: "Masks with exhalation valves or vents should not be worn to help prevent the person wearing the mask from spreading Covid-19 to others."
These masks have since been banned by most major airlines in the US, as well as some cities there, such as San Francisco and Denver.
Closer to home, health authorities in the Philippines have "strongly" advised against the use of masks with valves or vents.
But currently in Singapore, any face covering will pass muster, regardless of whether they reduce or increase the spread of droplets.