Can Face Shields and Masks with Valves Really Spread COVID-19?

    Can Face Shields and Masks with Valves Really Spread COVID-19?

    Late in August 2020, the government announced that aside from the use of face masks, plastic face shields for COVID-19 will become mandatory, too. But some people are finding it hard to wear both, forcing them to remove either their shield or their mask. But are plastic face shields for COVID-19 effective in reducing risk of infection?

    The problem is, a visualization study published in the journal of Physics of Fluids revealed that a face shield alone may not help prevent the spread of the coronavirus. Moreover, the research also showed that masks with a valve are ineffective in protecting the people around the wearer.

    Alarmingly, the investigators further discovered that different brands of masks offer different “degrees of leakage” no matter how similar they may seem.

    Simulating the Droplet Spread

    In the study, the researchers prepared a mannequin with a fog machine connected to its mouth. When activated, the fog machine will release a vapor of water and glycerine. This will simulate what happens when we cough.

    The investigators then used a laser to give a green glow to the vapor. This allows them to visualize how the vapor travels after the mannequin “coughs.”

    Afterward, they made the mannequin wear a face shield that’s similar to the plastic face shields that healthcare workers use against COVID-19. In the other setups, they used an ordinary N95 mask and another one with an exhale port (valve). Lastly, they also checked 2 different brands of commercially available plain surgical masks.

    Results of the plastic face shields for COVID-19 simulation

    When the mannequin “coughed,” the droplets initially deflected to the ground. However, some of the vapor remained suspended at the bottom of the shield. And just seconds after the simulated coughing, the droplets had floated to the front and sides of the mannequin, reaching a distance of about 0.9 meters.

    Furthermore, some of the droplets spread backward.

    Results of N-95 Mask with Valves Simulation

    In their next setup, the researchers visualized how the vapor will travel if the mannequin is wearing a regular N-95 mask with valves.

    Immediately after coughing, some of the droplets escaped through the gaps (top of the mask and bridge of the nose). But what’s alarming is that the majority of the vapor escaped through the valve. Initially, the droplets deflected downward, but soon after, they spread over a wide area.

    Now, to compare, the researchers then made the mannequin wear a regular N-95 mask without exhalation valves. The visualization test showed that after coughing, some of the droplets escaped through the gaps as well. However, the researchers stated that “the extent of exposure will be lower compared to that for either face shields or masks with valves.”

    Even the CDC recommends that we do not use masks with valves because, while it can protect the wearer, it does a poor job of protecting the people around the wearer. This is because the one-way valve releases the exhaled air, unfiltered. This can allow exhaled respiratory droplets to spread to others.

    plastic face shields for COVID-19

    Results of Surgical Masks Simulation

    After their simulation with plastic face shields for COVID-19 and mask with valves, the researchers proceeded in testing commercially available surgical masks.

    In this setup, they used 2 different brands of plain surgical face masks. Both of which, according to the manufacturers, were “not recommended for medical use.”

    As these masks are widely available to the public, researchers wanted to know the extent by which they can reduce COVID-19 spread.

    Brand A seems to be highly effective in stopping the “forward progression” of the vapor. There was leakage from the gaps, but it was “not excessive.” In fact, the researchers noted that “it is comparable qualitatively to leakage from the regular N95-rated mask.”

    Brand B, on the other hand, didn’t fare too well. Not only did the vapor escape through the gaps, but there was also significant leakage through the material itself.

    The conclusion is that while many masks appear to be superficially similar, there are still underlying differences. And these differences could affect their overall quality. The findings of this study hopefully help to enlighten the public about the wearing of masks and plastic face shields for COVID-19.

    The Study’s Conclusion

    After assessing the effectiveness of plastic face shields for COVID-19 and masks with valves, researchers came to the conclusion that face shields or masks with valves may not be as effective as a regular face mask when it comes to reducing the spread of aerosolized droplets.

    plastic face shields for COVID-19

    Face Shield Over a Face Mask: Is it More Effective?

    If plastic face shields for COVID-19 are not effective, should we continue using it? According to experts, yes, we should.

    Since it covers the whole face, it could block the entrance of the coronavirus through the nose, eyes, and mouth.

    In fact, a 2014 study revealed that at an 18-inch distance and a face shield can reduce the exposure from influenza-infused aerosol by up to 96%.

    Furthermore, medical institutions emphasize that when worn together with a properly-fitted face mask, face shields offer protection to the wearer. They even advise that when you know that you’ll be in “sustained close contact” with other people, it’s best to wear a mask underneath a face shield.

    Final Reminders

    So do plastic face shields for COVID-19 work? Wearing both a face shield and face mask can help us protect ourselves from the virus and reduce its spread. However, remember that unlike masks, plastic face shields for COVID-19 do not absorb the droplets. That’s why it’s important to regularly clean and disinfect it thoroughly after use.

    Clean it using alcohol wipes or wash it with soap and water. If the face shield sustains a crack or becomes damaged, don’t use it anymore as the quality has already been compromised.

    Learn more about COVID-19 here.

    Hello Health Group does not provide medical advice, diagnosis or treatment.

    Medically reviewed by

    Regina Victoria Boyles, MD


    Written by Lorraine Bunag, R.N. · Updated Dec 18, 2022