Do face shields offer better protection from coronavirus than masks?

For several weeks, citizens from Victoria in Australia have been required to wear a face covering when they leave home. And while we now have a clearer path out of lockdown, it is likely masks will be around for a while.

Meanwhile, people in other states with outbreaks have been encouraged to wear masks, and some people are simply choosing to wear one as a precaution.

But some people in the community, instead of opting for a traditional mask, are instead wearing a face shield.

This might offer some degree of protection – but it is probably not as good as a mask in preventing the spread of Covid-19.

What is a face shield?

A face shield is a film made from plastic or other transparent material designed to be worn like a visor. It is attached using a band that goes around the top of your head.

Think of a visor a welder wears to protect themselves from sparks and injury. Health-care workers use face shields to block bodily fluids from coming into contact with their face and potentially causing infection.

It is likely many people are choosing face shields during Covid-19 because they are experiencing discomfort wearing a mask – whether glasses fogging up, irritation around the ears or just that extra layer.

The term “face covering”, as per the Victorian government’s guidelines, is notably vague. It can include a face mask, a face shield, or a scarf or bandana.

The department of health does, however, recommend a mask over a face shield.

How effective are face shields?

A letter, published recently in the journal Physics of Fluids, reported on a laboratory experiment where scientists put face shields to the test.

They simulated coughing by connecting the head of a mannequin to a fog machine and then using a pump to expel the vapour through the mannequin’s mouth.

They found that while face shields stopped the droplets being propelled forwards, aerosolised droplets – those much smaller in size – lingered at the bottom of the shield and floated around at the sides. They eventually spread approximately 90 centimetres from the mannequins.

This is an interesting laboratory experiment, but not conclusive evidence face shields offer less protection than masks in the community.

A lack of research on the effectiveness of face shields means it is not possible to make any strong recommendations for or against their use.

Where does this leave us?

There is a lot we still do not know about this virus and how it spreads.

At present, we believe the virus is spread generally through close contact with an infectious person, contact with the droplets emitted when they sneeze or cough, or contact with surfaces these droplets have contaminated.

To establish an infection the virus enters your body through portals of entry: the mouth, nose and eyes.

Wearing a mask is intended to protect others if you have the infection, by blocking the droplets coming out of your mouth and nose. We call this source control. To a degree – though we have less evidence on this front – it is also likely to protect you, the wearer, by providing a physical barrier to your portals of entry.

A face shield may offer an advantage in that it provides a physical barrier over all your portals of entry – your eyes as well as your mouth and nose. Shields may also reduce the frequency of the wearer touching their face, and have the added benefit of allowing the person’s face to be seen (if they are not wearing a mask as well).

However, as they are not tight-fitting, aerosols may still enter and exit around the outside of a face shield, where it is not fitted in the same way a mask is. And we are continuing to accumulate evidence about the possible role of aerosolised transmission in the spread of Covid-19, which the World Health Organisation is closely monitoring.

Correct use is important too

Whatever face covering you choose, you must use it properly, and it must fit correctly.

Having masks slung under the chin, hanging off one ear, or your nose poking out over the top of the mask will make them markedly less effective. And of course, frequently touching and re-adjusting the mask means we are possibly contaminating our hands too.

If you do not intend to wear a mask properly or you are unable to, then a face shield is a better option. You can also wear a mask and a face shield together, should you wish to.

Like masks, there are a variety of face shields available, varying in quality and size. The department of health advises if you wear a face shield it should cover “the wearer’s forehead to below the chin area and wrapping around the sides of the wearer’s face”.

You should not share a face shield. If they are labelled disposable, do not reuse them. And if they are reusable you need to clean them regularly following the manufacturer’s instructions.

The upshot

Masks worn correctly are the best option. When wearing a mask is not possible, then a face shield is better than nothing. Neither will work well if not used properly and importantly, they do not replace physical distancing and hand hygiene.

Philip Russo is an Associate Professor, Director Cabrini Monash University Department of Nursing Research at the Monash University. Brett Mitchell is a Professor of Nursing, the University of Newcastle.

This article first appeared on The Conversation.