researchfinds that while wearing a surgical face mask can provide protection against airborne infection, face shields offer little or no protection. Evidencesuggests that SARS CoV-2, the virus that causes COVID-19, is transmitted when people expel virus-containing droplets when they sneeze or cough. Studieshave found that breathing and talking can expel droplets containing the virus. These particles remain airborne and may spread widely through a room.
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Throughout the COVID-19 pandemic, people have used plastic visors and face shields for protection against potential infection in shops and other places where crowds gather.
The study, conducted by researchers at Philipps University Marburg in Marburg, Germany, compared 32 types of masks intended for use in hospitals, including cloth and surgical masks, respirators, and face shields.
“To protect against airborne pathogens, a mask that [needs to] fit well around the nose and mouth and also have the ability to filter or prevent pathogens from crossing the material,” Dr. David Hirschwerk, an attending physician in infectious diseases at Northwell Health in New York, told Healthline.
The first experiment measured the filtration efficacy of different mask materials.
Each mask was attached to an air-collecting tube placed inside an airtight tank. An aerosol of a chemical called di(2-ethylhexyl) sebacate (DEHS) was pumped into the tank and aerosol particles caught in the collecting tube were counted with a particle counter.
According to the study findings, average filtration efficacy was lowest for the cloth masks at 28 percent, followed by noncertified surgical masks at 63 percent, and certified surgical masks at 70 percent. Unsurprisingly, KN95 respirator material filtered out 94 percent of particles, and FFP2 mask material was slightly better at 98 percent.
The second experiment measured air pressure on either side of the mask. Researchers found that surgical face masks had the lowest drop in pressure, providing the least resistance to breathing. Respirator-type masks had the highest pressure drop.
The last experiment checked the filtration efficacy of the masks as worn on a face.
This time the masks were placed on a “dummy head” outfitted with an artificial windpipe, instead of an air-collecting tube. The artificial head was the average size of someone in the United States and had a coating resembling skin for a more realistic mask fit.
The cloth masks and the noncertified surgical masks performed the worst, only filtering out between 11.3 and 14.2 percent of particles. Surprisingly, a type II surgical face mask had similar “as worn” filtration results at 47 percent as KN95 respirators at 41 percent. The FFP2 respirators showed the best filtration, blocking 65 percent of particles.
Face shields were found to have no significant effect at all.
“Members of the public should wear certified surgical face masks of good quality rather than cloth masks or face shields, which performed poorly in our study. Respirators should be reserved for medical staff,” said Dr. Christian Sterr, one of the study authors, in a statement.
Like many other respiratory infectious diseases,
Hirschwerk pointed out that although face shields are protective, they’re not enough to prevent infection in a high-risk environment.
“A surgical mask provides some protection to the wearer, but not as much as an N95 respirator,” he said. “Since there is the potential for a pathogen like SARS-CoV-2 to cause infection via the membranes associated with the eyes, the face shields can help reduce that risk. But, by themselves, face shields are insufficient in high exposure situations,” he said.
“The use of N95 for the general public is most likely unnecessary, especially if social distancing can be maintained,” said Dr. Teresa Murray Amato, chair of emergency medicine at Long Island Jewish in Queens, New York.
According to Murray, N95 masks are best in a healthcare setting for providers who will be in close proximity for an extended period with a patient who has COVID-19.
She added that as long as a surgical mask has not gotten soiled, wet, or damaged, it can be reused. However, the advice about using cloth masks will have to be reconsidered based on this study’s findings.
“The decision to wear a cloth versus a surgical mask had been made on personal preference, as the thought was that they appeared to have equal efficacy,” she said. “However, the recent study suggests that certified surgical masks may have better efficacy.”
Murray pointed out that the good news is that vaccines will continue to decrease the need for masking, and that, “we would encourage anyone who has not been vaccinated to talk with a trusted healthcare professional about any vaccine hesitancy.”
She also advised anyone with concerns about the type of mask they should be wearing to consult with their doctor.
Recent research finds that among many types of masks, surgical face masks are the best option for preventing infection with SARS-CoV-2. When used alone, plastic face shields offer mostly ineffective protection.
Experts say while the decision to use cloth or surgical face masks was left to personal preference, that advice may need to change according to the study findings.
They also say that thanks to COVID-19 vaccines, the need for masking will decrease in time. Those who are hesitant about the vaccine or have questions about masking should speak with a trusted healthcare professional.