Public health officials have recommended that people wear masks when social distancing is not possible for mitigation of the spread of the COVID-19 virus. Some governors are now mandating it. Science has indicated that mask-wearing helps prevent the spread, but what kind of masks actually work?
For many people, the idea that a mask is a good defense against COVID-19 coronavirus is a no-brainer. For other people, those who wear masks have no brain. Arguments will rage back and forth well after the pandemic ends. For now, however, mask wearing is becoming mandatory in certain circumstances.
But what kind should you wear? Well, if you’re one of those who wants their mask to actually work, you would do well to listen to the science folks at the University of Arizona. A team from U of A’s Mel and Enid Zuckerman College of Public Health have just reported their findings on this subject in the Journal of Hospital Infection, and they say not all masks are worth wearing.
Amanda Wilson, who is a candidate for a PhD in environmental health sciences, led a study assessing the infection-prevention capabilities of a variety of non-traditional mask materials. The findings may make you change your choice of mask. Or maybe not.
The team took a look at how various materials could protect you from infection after exposure times ranging from 30 seconds to 20 minutes while in a highly contaminated environment.
Their first finding was that wearing a mask during 30-second and 20-minute exposures to the virus that causes COVID-19 reduced the risk of infection by 44-99 percent and 24-94 percent, respectively. Mask material was a key variable. The risk reduction provided by any mask material was reduced as the duration of exposure lengthened, according to their findings.
“N99 masks, which are even more efficient at filtering airborne particles than N95 masks, are obviously one of the best options for blocking the virus, as they can reduce average risk by 94-99% for 20-minute and 30-second exposures, but they can be hard to come by, and there are ethical considerations such as leaving those available for medical professionals,” Wilson said.
If you can’t get your hands on N99 masks, all is not lost. Other options are available and effective. N95 and surgical masks fared well in terms of preventing infection.
One big surprise was vacuum cleaner filters. Yes, you read that right. Apparently, these can be slid into the pockets of masks to increase protection. Vacuum cleaner filters reduced the risk of infection by a whopping 83 percent during a 30-second exposure and by 58 percent during a 20-minute exposure.
While a vacuum cleaner filter may seem a pretty non-traditional mask material, there were other non-traditional materials tested as well. It seems antimicrobial pillowcases fared pretty well, as did cotton-blend fabrics and tea towels.
That scarf you have wrapped around your head to cover your nose and mouth? Not so great, say the researchers. You’ll get a 44 percent risk reduction at a 30-second exposure and only 24 percent at the 20 minute mark. Those people who thought they were cool by cutting off cotton t-shirt sleeves are also out of luck. According to the researchers, they may as well be mask-less.
“We knew that masks work, but we wanted to know how well and compare different materials’ effects on health outcomes,” said Wilson, who specializes in quantitative microbial risk assessment. Her job sounds like a barrel of laughs, doesn’t it?
Wilson and the other science folks involved drew their data from a variety of studies of mask material efficacy. They then used a computer model to simulate the risk of infection which incorporated a variety of factors in assessing effectiveness.
“One big component of risk is how long you’re exposed. We compared risk of infection at both 30 seconds and 20 minutes in a highly contaminated environment,” she said.
Of course, there are other conditions and factors which are difficult to build into models like this. How many people you are around, either in the immediate or over the course of time, as well as how far those people are from you plays a role in infection risk, regardless of mask material.
Another unpredictable variable is the size of respiratory droplets being spewed from an infected person. Larger virus-carrying droplets fall to the ground quicker than lighter, smaller ones. It’s a key reason why distance helps cut your exposure.
It’s also why one key research area right now is whether and/or how SARS-CoV-2, the virus which causes COVID-19, is spread through aerosol exposure. Based on previous research, the common belief was that the virus didn’t remain suspended in the air for very long. While that’s still likely the case, research is ongoing.
“Aerosol size can also be affected by humidity,” Wilson said. “If the air is drier, then aerosols become smaller faster. If humidity is higher, then aerosols will stay larger for a longer period of time, dropping out faster. That might sound good at first, but then those aerosols fall on surfaces, and that object becomes another potential exposure route.”
While it’s possible to get infected by touching a contaminated surface and then touching your nose or mouth, several studies have shown this to be a far less likely means of transmission than respiratory droplets.
Masks help reduce the risk of infection from respiratory droplets. This study found that time of contact impacts risk as well. The longer you spend in an environment where the virus is present, the higher your risk of infection.
“That doesn’t mean take your mask off after 20 minutes,” Wilson said, “but it does mean that a mask can’t reduce your risk to zero. Don’t go to a bar for four hours and think you’re risk free because you’re wearing a mask. Stay home as much as possible, wash your hands often, wear a mask when you’re out and don’t touch your face.”
There are a variety of ways in which masks protect the wearer and those with whom they come into contact. Wilson discussed two “intuitive” ways that masks filter larger aerosols and droplets. She referred to them as mechanical interception and inertial impaction.
“The denser the fibers of a material, the better it is at filtering. That’s why higher thread counts lead to higher efficacy. There’s just more to block the virus,” she said. “But some masks (such as those made from silk) also have electrostatic properties, which can attract smaller particles and keep them from passing through the mask as well.”
Both the inhalation rate of the mask wearer – the volume of air inhaled over a specific time period – and the concentration of the virus in the air were parameters included in the model developed by Wilson and her team.
“We took a lot of research data, put it into a mathematical model and related those data points to each other,” Wilson said. “For example, if we know people’s inhalation rates vary by this much and know this much virus is in the air and these materials offer this much efficiency in terms of filtration, what does that mean for infection risk? We provide a range, in part, because everyone is different, such as in how much air we breathe over time.”
Something that many mask wearers often ignore seems to be a very important aspect of mask effectiveness, according to Wilson. She noted that a mask with a solid seal on the face and that pinches at the nose will inevitably do a better job, regardless of material used. She also stated that you shouldn’t wear your mask below your nose or tuck it away beneath your chin when not in use.
“Proper use of masks is so important,” Wilson said. “Also, we were focusing on masks protecting the wearer, but they’re most important to protect others around you if you’re infected. If you put less virus out into the air, you’re creating a less contaminated environment around you. As our model shows, the amount of infectious virus you’re exposed to has a big impact on your infection risk and the potential for others’ masks to protect them as well.”
Whatever your thoughts about wearing masks, either indoors or outdoors, it looks like they are becoming a staple in our lives. That being the case, it’s good to know which materials are best suited for filtering out the COVID-19 virus. After all, if you’ve got to wear one, it might as well do its job well!
Keep the faith and keep after it!
Related Content –
Study Says Wearing Masks May Reduce COVID-19 Coronavirus Transmission
Nearly Half Of All COVID-19 Coronavirus Infections May Come From Asymptomatic People
Was The Early COVID-19 Coronavirus Infection Rate 80 Times Higher Than Estimated?
Journal Reference – Amanda M. Wilson et al. COVID-19 and non-traditional mask use: How do various materials compare in reducing the infection risk for mask wearers?, Journal of Hospital Infection (2020). DOI: 10.1016/j.jhin.2020.05.036