We get it. Wearing a mask can be uncomfortable. They’re hot. They get damp if you exert yourself. The elastics may hurt your ears. So it can be tempting to try using a face shield instead – a clear plastic shield that covers your face from your forehead down. But shields were never meant to be used alone when trying to prevent the spread of airborne infections. They should be used together with masks for optimum protection, which is why you see images of hospital staff and people in high-risk areas wearing both together.
Here is why face shields should not be used alone.
On one hand, face shields are rigid or semi-rigid clear plastic sheets that curve around your face, but they do not sit next to your skin on the cheeks or below your mouth. Their original use was to protect the wearer from splashes of body fluid that could hit their eyes and face. On the other hand, masks, when worn correctly, fit around the nose, cheeks and chin to keep your airborne droplets in and to keep outside droplets out.
Researchers from Florida Atlantic University College of Engineering and Computer Science performed experiments to look at how droplets acted when a person sneezed or coughed while wearing a face shield without a mask. Would the shield protect the people around them? The answer was no. What the researchers found was that although the shield did stop the initial spray of droplets after a sneeze or cough, the droplets then moved across the shield and spread out the sides and bottom of the shield, entering the surrounding environment.
In addition, while masks can filter out droplets as you breathe in, the open spaces around the face shields allow a flow of possibly contaminated air underneath the shield that you would then breathe in. Therefore, there is little protection from someone who may be speaking nearby, or coughing or sneezing.
In the same study, the researchers looked at masks that are sold with exhale valves, which manufacturers claim are more comfortable for breathing and just as safe as regular masks. These should not be confused with the official N-95 masks, which are specially designed for optimum safety. The valves on the other masks allow your breath to push through the mask every time you exhale. In other words, they do not filter out any viruses. Thus every time you breathe, if you have the virus, it is sent outside the mask into the open.
“Our observations suggest that to minimize the community spread of COVID-19, it may be preferable to use high quality cloth or surgical masks that are of a plain design, instead of face shields and masks equipped with exhale valves,” the researchers concluded.