Does a mask protect you from Covid when nobody else is wearing one?

If I am the only person wearing a mask in a store or other indoor location, am I really protected from infection?

It's true that masks work best when everyone in the room is wearing one. This is because when an infected person wears a mask, a large percentage of their exhaled infectious particles will be trapped, preventing the virus from spreading at the source. And with fewer virus particles floating around the room, the masks others wear would likely block those who escaped.

But there is also plenty of evidence that masks protect the wearer even when others around them are mask-free. The level of protection depends on the quality of the mask and its fit. In the event of a hotel breakout in Switzerland, for example, several employees and a guest who tested positive for the coronavirus only wore face protection (without masks); those who wore masks were not infected. And a study in Tennessee found that communities with mask requirements had lower hospital stays than areas that didn't require masks.

“Healthcare workers, scientists working with nasty pathogens, and workers who are exposed to potentially dangerous airborne particles at work rely on special masks like N95s Marr, a professor of engineering at Virginia Tech and one of the companies, for protection world leaders in virus transmission.

A number of laboratory studies have also documented that a mask protects the person wearing it, although the level of protection can vary depending on the type of mask, material, test setup and measurement of particle exposure.

Updated

9/21/2021, 6:34 p.m. ET

But the bottom line of all studies is that a mask reduces the potential exposure of the person wearing it. Here are some of the results.

• A study by the Centers for Disease Control and Prevention found that a standard surgical mask only protected the wearer from about 7.5 percent of the particles produced by a simulated cough. But knotting the loops and tucking in the sides of the medical mask reduced exposure by nearly 65 percent. (Watch this video to see the "knot and tuck" method.) Covering the surgical mask with a cloth mask, a technique known as double masking, reduced exposure to the simulated cough particles by 83 percent.

• A study by Virginia Tech looked at how well homemade masks, surgical masks, and face shields protected the wearer based on particle size. Research showed that most masks can block very large particles, such as when sneezing. However, when the researchers looked at the smaller aerosol particles, which are the hardest to block, protection ranged from near zero with a face shield to about 30 percent protection with a surgical mask. (The percentages in the study cannot be directly compared to the CDC Knots-and-Bisen Study because the test methods were different.) Based on the results, Dr. Marr and her colleagues concluded that a two-layer fabric mask made of flexible, close-knit fabric in combination with a filter material (such as a coffee filter or a face mask) could provide good protection by reducing 70 percent of the most penetrating particles and 90 percent or holds back more of the larger particles. They also found that headbands or straps offered a better fit than ear loops.

• A study from Tokyo tested how well different types of masks protect the wearer from actual coronavirus particles. The study showed that even a simple cotton mask offered the wearer some protection (17 to 27 percent). Medical masks performed better, including a surgical mask (47 to 50 percent protection), a loosely fitting N95 (57 to 86 percent protection), and a tight fitting N95 (79 to 90 percent protection).

• While many laboratory studies test masks with mannequin heads, a 2008 study in real people measured how well masks can protect the wearer from a respiratory virus. Study participants wore different types of masks that were equipped with special receptors that could measure the particle concentration on both sides of the masks. In this study, cloth masks reduced exposure by 60 percent, surgical masks by 76 percent, and N95 masks by 99 percent.

While the laboratory studies all show that a mask can protect the wearer, the performance of the masks in the real world depends on a number of variables, including consistent use of the masks, whether a person is in high risk situations, and the rate of infection in the community . A Danish study of 6,000 participants, half of whom were asked to wear masks, showed no benefit in wearing masks, but the study was widely criticized for its poor design.

The laboratory studies have shown that a high quality medical mask, such as an N95, KN95, or KF94, works best. While vaccinations are the best protection against Covid-19, even those who have been vaccinated are advised to avoid crowds or large groups indoors if the vaccination status of others is unknown. Since the Delta variant is far more contagious than other variants, Dr. Marr also to wear the best quality mask possible when you can't keep your distance or be outdoors – or when no one is masking themselves around you.

"If I am in a situation where I only have to rely on my mask for protection – unvaccinated people may be present, it is full, I don't know anything about the ventilation – I would wear the best mask in my closet, it's an N95, ”said Dr. Marr. "Because Delta has proven so much more easily transferable and can transfer vaccinated people, we need to wear the best possible masks in high-risk situations."