University of Arizona
July 20, 2020 AP News
It's intuitive and scientifically shown that wearing a face covering can help reduce the spread of the novel coronavirus that causes COVID-19. But not all masks are created equal, according to new University of Arizona-led research.
Amanda Wilson, an environmental health sciences doctoral candidate in the Department of Community, Environment and Policy in the Mel and Enid Zuckerman College of Public Health, is lead author on a recent study published in the Journal of Hospital Infection that assessed the ability of a variety of nontraditional mask materials to protect a person from infection after 30 seconds and after 20 minutes of exposure in a highly contaminated environment.
When the researchers compared wearing masks to wearing no protection during 20-minute and 30-second exposures to the virus, they found that infection risks were reduced by 24-94% or by 44-99% depending on the mask and exposure duration. Risk reduction decreased as exposure duration increased, they found.
"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.
The next best options, according to the research, are N95 and surgical masks and, perhaps surprisingly, vacuum cleaner filters, which can be inserted into filter pockets in cloth masks. The vacuum filters reduced infection risk by 83% for a 30-second exposure and 58% for a 20-minute exposure. Of the other nontraditional materials evaluated by the researchers, tea towels, cotton-blend fabrics and antimicrobial pillowcases were the next best for protection.
Scarves, which reduced infection risk by 44% after 30 seconds and 24% after 20 minutes, and similarly effective cotton t-shirts are only slightly better than wearing no mask at all, they found.
"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.
Wilson and her team collected data from various studies of mask efficacy and created a computer model to simulate infection risk, taking various factors into consideration.
"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.
Other conditions that impact risk of infection are the number of people around you and their distance from you, she said.
The size of virus-transporting droplets from sneezes, coughs or even speech is also a very important factor. Larger, heavier droplets carrying the virus drop out of the air faster than smaller, lighter ones. That's one reason distance helps reduce exposure.
"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."
The study also showed that the more time a person spends in an environment where the virus is present, the less effective a mask becomes.
"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."
Masks protect the wearer and others in a number of different ways. Wilson said there are two "intuitive ways" that masks filter larger aerosols: 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."
The model developed by Wilson and her colleagues included parameters such as inhalation rate -- the volume of air inhaled over time -- and virus concentration in the air.
"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."
Wilson also said it's important for a mask to have a good seal that pinches at nose, and she noted that people shouldn't wear a mask beneath the nose or tuck it under the 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."
Materials provided by University of Arizona. Original written by Mikayla Mace. Note: Content may be edited for style and length.
How to Choose the Best Cloth Face Mask for You
UPDATED SEPTEMBER 11, 2020
Any mask is better than no mask to help slow the spread of the coronavirus, and now that everyone and their grandparents are selling cloth face masks, you have options. Tens of thousands of them. (Around 15,000 listings on Etsy alone.) As with regular cloth face masks, the key is to create multiple layers and a good seal. We consulted a range of authorities, from fashion designers and textile experts to aerosol scientists and infectious disease specialists, to zero in on the small but crucial design details that have an outsize impact on how a mask fits and feels, and—by extension—how it helps prevent person-to-person viral transmission.
Because how well a mask works involves myriad factors (the size of a person’s head and facial features, their behaviors and environment), we couldn’t possibly identify the most effective mask for every person and every situation. Based on extensive research and preliminary fit and comfort testing, however, we do have a few recommendations for adjustable masks that we think will cover most faces comfortably and work well when worn properly. After all, the “best” cloth face mask is the one you will wear and not fuss with. (For advice on the best cloth face masks for children, see our buying guide just for kids.)
Adjustable ear loops, stretchy fabric
The slim elastic ear loops on this mask are gentler on ears than most thicker varieties. Cord stoppers, a sturdy nose-bridge wire, and a swimsuit-material-like outermost layer mean this mask should mold easily to most faces. Its two-ply construction is already quite dense, but you can insert an additional layer (not included) into its filter pocket. The easy-on, easy-off design is great for quick errands, but the fabric can feel hot with extended wear.
May be out of stock
*At the time of publishing, the price was $30.
Ear loops and headband options in one
This triple-layer poly-cotton mask is lingerie-material light but office-appropriate sleek. With cord stops on the ear loops, and a soft but effective nose-bridge wire, you can easily get a good fit before running out the door. Use the enclosed back-of-the-head hook, if you like, to relieve ear pressure. An easy-access pocket in this mask accommodates a filter (not included).
Heavy and lightweight options, secure headbands
The solid-color versions of this two-ply cone mask have the substantive, tight-weave feel of cotton-canvas painter’s pants; the plaids are made of the lighter performance fabric used in the cycling apparel the company is known for. Each has a pocket for a filter (two included). The elastic headbands stay put on hair better than most, and together with the pliable nose-bridge wire and a choice of three sizes, they allow for a nice, close fit.
Lots of options and a tall silhouette
This two-layer cotton mask offers more options than most—not only in color, but also in fit, fasteners, and layers: Choose from small or large sizes as well as designs with adjustable ear loops or around-the-head elastic bands; plus, a washable filter (included) slips in easily when you need it. The nose-bridge wire keeps its shape, the chin coverage is better than most, and the cinched sides of this mask allow the fabric to tent up higher off the face, providing more breathing room. (If you're between sizes, size up and adjust the fasteners to achieve a better seal.)
Generous pleats, adjustable drawstrings
This all-cotton, two-layer mask feels like a denim shirt. Thanks to pleats and a spaghetti tie looped into a drawstring system, it can adjust to fit most heads and facial features, including those more generously sized. (A tester with a full beard found this mask fit him best.) A filter pocket accommodates additional layers of your choice (none included), and there’s a sturdy nose-bridge wire.
Understandably, most people would prefer a mask that fits like a proverbial glove, traps all incoming and outgoing viruses, lets you gulp in fresh air with abandon, and feels as if it isn’t even there. Unfortunately, that mask doesn’t exist. Shopping for a cloth face mask is an exercise in compromises. Generally speaking, the better a mask blocks respiratory droplets, the harder it is to breathe through, said Bryan Ormond, an assistant professor of textile engineering at North Carolina State University’s Textile Protection and Comfort Center. Conversely, the easier it is to breathe through a mask, the less potentially protective it is. The best a non-medical mask can do is align closely to the curves of your face, cover your nose and mouth, and feel comfortable enough that you won’t fuss with it as you go about your day. In this guide, we’ll walk you through the latest research on cloth face coverings, help you build a collection of masks that suit your various needs, and explain how prioritizing fit and comfort can lead to better protection—for others and even, possibly, for yourself.
Shopping for a cloth face mask is an exercise in compromises.
Above, we’ve linked to in-stock masks with design details that the experts we interviewed said they looked for when shopping for themselves, and that we found greatly impacted fit and comfort. These features include moldable nose-bridge wires; cord stoppers, adjustable headbands, or ties; and filter pockets. We’ll continue to take notes as we slog through supermarket runs and workouts in the thick heat of summer, throw the masks into the wash, and field feedback from our long-term testers and our readers. We’ll also keep searching for promising options based on the latest science and people’s evolving needs as the seasons change. As long as masks remain a staple in daily life, we’ll be here with updates.
The Best And Worst Face Masks For COVID-19, Ranked by Their Level of Protection
ARIA BENDIX, BUSINESS INSIDER
16 JULY 2020
The science is clear: Face masks can prevent coronavirus transmission and save lives.
A preliminary analysis of 194 countries found that places where masks weren't recommended saw a 55 percent weekly increase in coronavirus deaths per capita after their first case was reported, compared with 7 percent in countries with cultures or guidelines supporting mask-wearing.
A model from the University of Washington predicted that the US could prevent at least 45,000 coronavirus deaths by November if 95 percent of the population were to wear face masks in public.
But not all masks confer equal levels of protection.
The ideal face mask blocks large respiratory droplets from coughs or sneezes – the primary method by which people pass the coronavirus to others – along with smaller airborne particles, called aerosols, produced when people talk or exhale.
The World Health Organisation recommends medical masks for healthcare workers, elderly people, people with underlying health conditions, and people who have tested positive for the coronavirus or show symptoms.
Healthy people who don't fall into these categories should wear a fabric mask, according to WHO. The Centres for Disease Control and Prevention also recommends cloth masks for the general public.
But even cloth masks vary, since certain types are more porous than others.
"It depends on the quality," Dr. Ramzi Asfour, an infectious-disease physician in Marin County, California, told Business Insider.
"If you're making a cloth mask from 600-thread-count Egyptian cotton sheets, that's different than making it from a cheap T-shirt that's not very finely woven."
Over the past few months, scientists have been evaluating the most effective mask materials for trapping the coronavirus. Here are their results so far, from most to least protective.
Two medical-grade masks, N99 and N95, are the most effective at filtering viral particles.
There's a reason agencies recommend reserving N99 and N95 masks for healthcare workers first: Both seal tightly around the nose and mouth so that very few viral particles can seep in or out. They also contain tangled fibres to filter airborne pathogens.
A study published in the Journal of Hospital Infection last month evaluated more than 10 masks based on their ability to filter airborne coronavirus particles.
The researchers found that N99 masks reduced a person's risk of infection by 94 to 99 percent after 20 minutes of exposure in a highly contaminated environment. N95 masks offered almost as much protection – the name refers to its minimum 95 percent efficiency at filtering aerosols.
Another recent study also determined that N95 masks offered better protection than surgical masks.
Disposable surgical masks are a close second.
( Sebastian Condrea/Moment/Getty Images)
Surgical masks are made of nonwoven fabric, so they're usually the safest option for healthcare workers who don't have access to an N99 or N95 mask.
An April study found that surgical masks reduced the transmission of multiple human coronaviruses (though the research did not include this new one, officially called SARS-CoV-2) through both respiratory droplets and smaller aerosols.
In general, surgical masks are about three times as effective at blocking virus-containing aerosols than homemade face masks, a 2013 study found. But healthcare workers should still have access to them first.
"The official guidelines are cloth masks because we don't want to take those masks away from medical workers who might need them more," Asfour said.
"Hybrid" masks are the safest homemade option.
In a recent paper that hasn't yet been peer-reviewed, researchers in the UK determined that "hybrid" masks – combining two layers of 600-thread-count cotton with another material like silk, chiffon, or flannel – filtered more than 80 percent of small particles (less than 300 nanometres) and more than 90 percent of larger particles (bigger than 300 nanometres).
They found that the combination of cotton and chiffon offered the most protection, followed by cotton and flannel, cotton and silk, and four layers of natural silk.
The researchers suggested that these options may even be better at filtering small particles than an N95 mask, though they weren't necessarily better at filtering larger particles.
The team also found that two layers of 600-thread-count cotton or two layers of chiffon might be better at filtering small particles than a surgical mask.
Three layers of cotton or silk are also highly protective.
WHO recommends that fabric masks have three layers: an inner layer that absorbs, a middle layer that filters, and an outer layer made from a nonabsorbent material like polyester.
A University of Illinois study that's still awaiting peer review found three layers of either a silk shirt or a 100 percent cotton T-shirt may be just as protective as a medical-grade mask. Silk in particular has electrostatic properties that can help trap smaller viral particles.
Vacuum-cleaner bags are a DIY alternative to surgical masks.
The Journal of Hospital Infection study found that vacuum-cleaner bags (or vacuum-cleaner filters inserted in a cloth mask) reduced infection risk by 83 percent after 30 seconds of exposure to the coronavirus and by 58 percent after 20 minutes of exposure in a highly contaminated environment.
The material was almost as good at filtering aerosols as surgical masks, the researchers found.
That could be enough protection to stop an outbreak. A May study found that universal mask-wearing would bring an epidemic under control even if the masks were only 50 percent effective at trapping infectious particles.
Tea towels and antimicrobial pillowcases aren't ideal materials, but they're better than a single layer of cotton.
Tea towels and antimicrobial pillowcases were the next-best alternatives to vacuum-cleaner bags or filters, the same study found.
Tea towels need to be tightly woven to confer protection, the researchers said.
Antimicrobial pillowcases (usually made of satin, silk, or bamboo) were preferable to a standard cotton pillowcase, they found.
Wrapping a scarf or cotton T-shirt around your nose and mouth isn't particularly effective at filtering the coronavirus, but it's still better than nothing.
The UK researchers found that a single layer of 80-thread-count cotton was among the least effective materials at blocking coronavirus particles both large and small.
Scarves and cotton T-shirts reduced infection risk by about 44 percent after 30 seconds of exposure to the coronavirus, the Journal of Hospital Infection study found. After 20 minutes of exposure in a highly contaminated environment, that risk reduction dropped to just 24 percent.
But that's better than zero.
Even a loosely fitted cotton mask "substantially decreases" the spread of viral particles when an infected person coughs or sneezes, researchers in India recently determined.
They found that infectious droplets travelled up to 16 feet when a person wasn't wearing a mask, compared with just 5 feet when particles leaked out the sides of a face mask.
Single-layer cotton masks are preferable to single-layer paper masks.
The UK researchers found that people who wore cotton masks had a 54 percent lower chance of infection than people who wore no masks at all. People who wore paper masks had a 39 percent lower chance of infection than the no-mask group.
Unlike a surgical mask, which is typically pleated and made of three layers of fabric, paper masks are thinner, so they confer less protection.
How you wear your mask matters too.
(Andreas Solaro/AFP/Getty Images)
The protectiveness of a mask – including N95 and surgical masks – declines considerably when there is a gap between the mask and the skin.
"It's about the seal of the mask," Asfour said. "You have to make sure there's no air leak."
Even so, research has suggested that wearing masks improperly or sporadically could still reduce transmission.
In an editorial published Tuesday in the Journal of the American Medical Association, CDC Director Robert Redfield predicted that the universal adoption of face masks could bring the US's outbreak under control in as little as four weeks.
This article was originally published by Business Insider.