International health chiefs last week declared a ‘global emergency’ and the first two cases of the deadly coronavirus, inevitably, emerged in the UK.

A further 83 Britons have now been evacuated from Wuhan – where the virus was first recognised – and are being held in quarantine in a Merseyside hospital.

NHS bosses reassured the public about ‘robust measures’ already being in place to prevent the spread of the illness. With the number of confirmed cases soaring worldwide, as well as the toll of deaths, an increasing number of people want to know: what can I do to best protect myself?

Desperate measures: Masks in China made of tin foil and tape, left, and a grapefruit skin, right. Last week there were mask shortages, with people resorting to makeshift protection

In many Asian countries, face masks – the reusable cloth ones, or the disposable surgical type worn by doctors and nurses – have been a common sight on commuters for decades, often as protection from pollution.

The spectre of successive health outbreaks since SARS in 2002 – including H1N1 ‘swine’ flu, ‘avian’ or bird flu, and MERS – all of which could kill, also means the public are on high alert.

Last week in China, amid nationwide shortages of masks, people began resorting to using bras, plastic bags and containers over their heads as makeshift protection.

The new virus has so far proved fatal in about three per cent of infected patients. This doesn’t sound high, but it is about the same death rate as the 1918 ‘Spanish’ flu that killed millions worldwide.

And that number may well rise.

So concern is understandable. But are masks – which, except for being worn by a few supermodels and celebrities, have never really caught on in the UK – a good idea?

Some masks could be worse than useless

There are three basic types of face mask you can buy. First are washable cloth masks – often sold in bright colours. They’ve become something of a fashion item in Asia.

Then there is the light, loose surgical mask, made of a type of paper and other fibres. These are designed to be thrown away after each use.

Finally, there are close-fitting masks worn by hospital staff – and some London cyclists and builders – called the N95 or FFP3 ‘respirators’. These are also single-use.

The effectiveness of each type in any given outbreak will depend on how the virus spreads.

Home-made: Others used plastic bottles (right) and even lettuce leaves (left). You can buy washable cloth masks, light, loose surgical masks or close-fitting masks

People wearing protective face masks walk in a commuter train station in Bangkok, Thailand

Some viruses travel in larger ‘droplets’ of saliva or mucus. These are coughed or sneezed out by an infected person, propelled forward, and don’t float in the air. They can be either directly inhaled or, commonly, picked up from surfaces by the hands, and then transferred when someone touches their face.

Other viruses are airborne or ‘aerosol’, and exist in tiny particles of moisture – in our breath and floating in the air – and spread more easily. Despite their popularity, there’s not much evidence that surgical masks are an effective way to stop infection, although they may provide a physical barrier, protecting against any significant spray of saliva or mucus.

Viruses and other pathogens can live on surfaces. People then touch these surfaces with their hands, and then touch their mouth or nose – infecting themselves. Surgical masks may have a use in preventing this kind of transmission.

However, we don’t yet know how the coronavirus spreads. If it travels via the ‘droplet’ method, as SARS and MERS mainly did, surgical masks may help protect you from particles expelled from coughs or sneezes. But viruses aren’t always one or the other, according to researchers.

Both SARS and MERS also spread, occasionally, via fine aerosols.

And because most masks do not fit closely around the face, tiny airborne particles could still get through to the mouth and nose.

As Professor Raina MacIntyre, of the University of New South Wales in Sydney, Australia, says: ‘The effectiveness of surgical masks against airborne infections is low, because they do not provide a seal around the face and do not have good filtration.’

A girl, left, with an orange-peel mask and a man, right, wearing a large plastic bottle over his head, with his mouth also covered by a face mask

Some viruses travel in larger ‘droplets’ of saliva or mucus. These are coughed or sneezed out by an infected person, propelled forward, and don’t float in the air (file photo)

And the cloth masks popular in Asia (and make-shift bra masks, in case you were considering one) may be worse than useless.

Prof MacIntyre led the only scientific study of them so far, in 14 hospitals in Hanoi, Vietnam.

‘Cloth masks have no efficacy at all, and may even increase your risk of infection – especially if they are not washed regularly,’ she says.

However, fellow University of New South Wales researcher Dr Abrar Chughtai says: ‘Something is better than nothing.’

If the mask fits, it will protect you

Most effective, research suggests, is the close-fitting mask. Doctors and nurses are advised to wear these against germs that are properly airborne, in tiny particles that float on air currents and go deep into your lungs – like measles, the most contagious virus known.

A tight fit is essential (they don’t work with a beard) to keep out these particles.

Doctor Li Zhang, of Wuhan’s Jinyintan Hospital, is fighting the new coronavirus at the epicentre.

Writing this week in the British medical journal The Lancet, he was clear: medical staff need the disposable close-fitting masks that stop fine aerosols.

Workers produce masks at the Thai Hospital Product Company in Bangkok. Doctors and nurses are advised to wear the close-fitting mask, which research suggests is the most effective

But do ordinary people? They are uncomfortable to wear – not to mention expensive, working out at about £1.50 each on online sites.

And, according to Dr Abrar Chughtai and Prof Raina MacIntyre, the tight-fitting kind should be reserved for medical responders anyway. They are at the greatest risk, to themselves and others – and were key in spreading SARS.

Prof David Heymann, of the London School of Hygiene and Tropical Medicine, who led the fight against SARS while at the World Health Organisation, is more dubious about the value of wearing a mask.

‘In general they are not known to be effective in protecting against infection,’ he says.

Viruses invade eyes, too, and masks don’t cover those.

Surgical masks can, however, stop someone from infecting other sick people. At the Beijing United Family Hospital last week, all visitors were required to wear surgical masks – to protect patients.

The best defence? Washing your hands

Despite questions over the effectiveness of masks, worried Chinese are buying them – with retailers selling out and reports of prices soaring ten-fold.

The World Health Organisation advises wearing washable or disposable gloves in public, and washing hands regularly with soap or alcohol-based cleaner (file photo)

With most medical protective equipment made in China, that shortage could spread. Some European countries are also warning of shortages. You could improvise, of course, with some in China even resorting to orange rinds and plastic bottles cut in half.

‘You can use bras as masks – which is what people did during SARS 17 years ago when masks sold out,’ says Julian Tang, of the Leicester Royal Infirmary.

But there are, perhaps, more useful things you can do.

The World Health Organisation advises wearing washable or disposable gloves in public, and washing hands regularly with soap or alcohol-based cleaner. Avoid touching doorknobs and other public surfaces. Stand 3ft from sick people and cough and sneeze into a tissue – then throw it away and wash your hands. Don’t share towels.

Asked what single thing he would advise, Prof Heymann doesn’t hesitate. ‘Handwashing,’ he says.

So maybe you don’t need to worry about masks after all.