Coronavirus: How well do face masks protect against viruses, droplets and dust? | Science| In-depth reporting on science and technology | DW | 08.02.2020
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Coronavirus: How well do face masks protect against viruses, droplets and dust?

Fearing coronaviruses, many people try to protect themselves with a surgical face mask. In many Chinese cities it is already compulsory to wear them. But do they really help stave off the virus?

The simple mouth and nose protector — a mask made of a rather thin paper fleece, which is knotted behind the head with ribbons - was formerly used almost exclusively in operating theaters.

Doctors and assistants wear this mouthguard primarily to prevent their patients on the operating table from being infected with germs and pathogens. If the wearer of the mask coughs or sneezes, for example, most of the droplets from the mouth and throat get caught in the mask. 

In the long run, however, this only works if the mask is changed regularly and disposed of hygienically and safely. In surgery, doctors must change their mask at least every two hours. If, on the other hand, a mask of this type is worn repeatedly, it quickly loses its effectiveness. 

Read more: Coronavirus, cold or flu? How to tell the difference

How much protection does the mask provide?

The wearer of the mask can protect himself against droplet and smear infections, but only to a very limited extent. Although the virus usually enters the body through the mouth or eyes — if there are no open wounds — the hands play the most important role in transporting the virus.

If you decide to wear a mask, you should probably also opt for protective goggles. The surgical masks, albeit less effective in keeping the viruses out, merely function as a constant reminder not to touch your nose with your hands when it itches. Neither should you rub your eyes.

Half masks offer better protection

In addition to surgical masks, which look more like multi-layer disposable kitchen towels, there are also half masks with a real filter effect. These are more familiar to thsoe who work in dusty environments or with aerosols. They are available either as disposable masks, usually made of strong pressed cellulose with a filter element and an exhalation valve, or as plastic masks in which a suitable filter is then inserted. 

Read more: Coronavirus vaccine — a race against time

A woman, wearing a FFP 3 protective mask. (picture-alliance/dpa/R. Weihrauch)

Only a FFP 3-grade mask will filter out enzymes and viruses.

In the European Union these types of masks are divided into threeFFP protection classes (filtering face piece). Although masks of protection level FFP1 are still better than surgical masks, they do not offer the desired protection against viruses. They are intended for carpenters, for example, who work at a band saw with an vacuum extraction system. Workmen may wear them to catch the coarser dust, which the vacuum cleaner is unable to catch. Or a bricklayer can put them on before mixing cement with a trowel, kicking up some dust.

Only FFP-3 class masks effectively protect the wearer from droplet aerosols, protein molecules, viruses, bacteria, fungi and spores, and even from highly dangerous dusts such as asbestos fibres.

If a mask is needed - then it needs to be the right one

Such high-quality filter masks can protect the wearer - unlike simple surgical masks - from infection due to their design. In other words, also from a highly infectious pathogen such as measles or tuberculosis. 

Read more: The power of masks

A Polish military officer, wearing a complete body suit and a military gas mask is caring for patients, who arrived in Wroclaw from Wuhan. (picture-alliance/AP Photo/A. Rataj)

Effective but not suitable for just everybody: Military gas mask and complete body protection.

But here too, protection only works if many other protective measures are taken at the same time: Strict hygiene when putting on a mask, protective goggles, gloves and plastic apron or overall, proper disposal of possibly contaminated disposable items and regular hand washing. In addition, the surroundings must always be systematically disinfected. 

These masks - together with all other protective clothing - are therefore used in quarantine stations, for example, where patients who are already infected are cared for. The medical staff has to put on and take off all the protective clothing, including the protective mask, at considerable expense.

For travelling in public transport or working at a keyboard at alternating workstations, which happen to be among the worst germinators of all, this effort would be completely disproportionate.

And what about tear gas?

The demonstrators in Hong Kong also wore a variety of different protective masks - from simple surgical masks to half masks with filters.

Surgical masks are probably only effective in conceiling the demonstrators' identity. However, when the police fire tear gas grenades that spray an aerosol, only FFP-3 filters can provide some protection. To prevent the tear gas from getting into the eyes, airtight protective goggles are absolutely necessary. 

Read more: Proof of poison gas: Circumstantial evidence is key

Proteste in Hongkong (picture-alliance/dpa/Zuma/C. Long Hei)

Only the man in the center has effective protection against tear gas.

However, occupational safety filters from the hardware store do not offer any real protection. A proper full face gas mask with a military NBC filter would do the job.

And of course this also provides good protection against viruses. But in everyday life nobody wants to walk around like this.

Best protection: Don't forget to wash your hands

All masks and goggles are of little use if the most important hygienic principles are neglected. For example, if you come home after a long bus or train ride, where you touched handrails and handles, take off the mask and scratch your nose, You could have left out the protective mask just as well.

It's the same at work: if you have been typing on the computer keyboard all morning and then go to lunch without washing your hands first, you take a considerable risk. Then, wearing a mask at the computer workstation would have been of little use either.

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