In spite of the Government urging people who are well not to wear masks, many still do, and the sale of masks remains brisk.

Some people are asking if this government advice has been issued in order to keep its stockpile intact, and if masks really do stop people from catching the virus.

AskST looks at how people can best protect themselves.

Q Will wearing a mask fully protect me against the virus?

The answer is no. That is not to say that masks are useless. They do help to some degree if used correctly. But the amount of protection varies with the type of mask.

What about putting handkerchief or tissue paper over your mouth and nose when someone nearby coughs and sneezes?

Again, the answer is that this too probably helps to some extent.

Among masks, the N95 gives the highest level of protection, but it is still not foolproof.

Studies in healthcare institutions indicate that it provides more protection than surgical masks.

But it is difficult to wear these masks for long and other than within healthcare institutions where the risk of infection may be high, it is certainly not recommended.

Dr Shawn Vasoo, acting clinical director of the National Centre for Infectious Diseases, said a study involving more than 2,800 healthcare workers published in the Journal of the American Medical Association last year, found that N95 and surgical masks provided similar levels of protection against influenza - not the coronavirus - in an outpatient setting.

Surgical masks, if worn improperly - such as when there are gaps on the side of the face or if worn by people with beards - will let viruses through.

Dr David Carrington, a clinical virologist at St George's, University of London, told BBC News that "routine surgical masks for the public are not an effective protection against viruses or bacteria carried in the air" because they are too loose, have no air filter and leave the eyes exposed.

A study of reusable cloth masks carried out in Vietnam involving more than 1,600 healthcare workers found that "moisture retention, reuse of cloth masks and poor filtration may result in increased risk of infection".

In the same study published in the British Medical Journal in 2015, even some in the group wearing surgical masks got infected. These results were from healthcare workers who saw an average of 36 patients a day, over a four-week period.

The United States' Mayo Clinic said using masks and hand sanitisers to protect against influenza is more effective than wearing masks alone. This is partly because people who wear masks may be touching them with unclean hands, for example when they want to eat or drink.

A behavioural observation study of 23 medical students at the University of New South Wales found that they touched their faces an average of 26 times an hour, and 44 per cent of the times that they touched their faces involved contact with mucous membrane including in the eyes and nose.

Another problem with surgical masks is the longer you wear one, the less effective it becomes, especially if it gets damp from your breath.

So wearing masks may give a false sense of security, and people may become lax about taking other protective steps, such as washing their hands frequently.

Q Is washing my hands more important than wearing a mask?

Speaking in Parliament last Monday, Health Minister Gan Kim Yong said that based on what is known so far, "the virus is carried within droplets emitted from an infected person over a short distance, such as when the person coughs or sneezes".

He added: "If these droplets come into contact with the eyes, nose or mouth of an individual, directly or indirectly through hands that have come into contact with these droplets, the individual may become infected."

It is not certain yet, but the current belief is that the virus could remain infective on surfaces for two to three days.

Mr Gan said: "As such, medical professionals both overseas and in Singapore have advised that the most effective way that we can protect ourselves is to practise good personal hygiene."

Since the coronavirus is now known to be transmissible through faeces, it is even more important to have good hand hygiene.

The World Health Organisation and the United States Centres for Disease Control and Prevention are also telling people not to use face masks if they are not sick.

Instead, they advise people to wash their hands thoroughly and regularly throughout the day and to avoid touching their eyes, nose and mouth with unwashed hands.

Q To wear a mask or not?

If you are sick, wear a mask to prevent spreading your germs.

Dr Vasoo said masks "provide a barrier to large particles expelled by the wearer", thus reducing the risk to others.

Better still, stay home if you are sick.

If you are well and want to wear a mask for protection, make sure you wash your hands before putting it on and every time you touch it as you could transfer germs from your dirty hands to the mask.

Also ensure that you are wearing the mask properly: It should fit snugly against your face with no gaps to allow the viruses to get through.

Change the mask when it becomes soiled or damp as this reduces its effectiveness.

Be prepared to wear masks for at least a few weeks, as the coronavirus problem is not likely to disappear any time soon.