Fact check: Masks can keep out COVID-19 particles even though smaller than dry wall dust

Devan Patel

The claim: If masks cannot keep out drywall particles, they cannot keep out coronavirus, which is smaller

As the pandemic has persisted, social media posts have questioned the effectiveness of some masks to stop coronavirus because of their inability to stop the transmission of larger particles.

“The average size of drywall dust particles is 3 microns,” a Facebook post on July 7 states. “The average size of a coronavirus particle is .3 microns. If masks can’t prevent drywall dust getting through, how can they possibly prevent something 10x smaller from getting through?”

The post includes two images of a person with an ear-loop surgical mask resting underneath his chin and lines of white dust on the sides of his nose and around his eyes, above where a properly worn mask would sit. To date, one post has more than 20,000 shares and over 1,300 comments, and many other versions appear on Facebook.

USA TODAY has reached out to the user who posted the viral meme for comment.

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What are the mask recommendations?

With more than 5 million cases and 162,000 deaths from COVID-19 in the United States, according to Johns Hopkins University data, infectious disease experts still recommend wearing a mask in public and physical distancing.

The Centers for Disease Control and Prevention began recommending the use of masks in April.

“Wear cloth face coverings in public settings where other social distancing measures are difficult to maintain, such as grocery stores, pharmacies, and gas stations. Cloth face coverings may slow the spread of the virus and help people who may have the virus and do not know it from transmitting it to others,” guidance from the CDC states.

More than 30 states have instituted a statewide order requiring masks in public places. In states without a mandate, local governments have stepped in and instituted their own orders to slow the spread even at the risk of facing litigation.

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In Florida, where the number of cases continues to balloon, more cities and counties are issuing local mandates as Gov. Ron DeSantis has resisted issuing a statewide order, despite Florida becoming the second state to surpass half a million cases.

“I would have liked to see mask orders earlier. Unfortunately, there have been a lot of mixed messages from many places about transmission and whether masks are useful,” Cindy Prins, Master of Public Health Program Director at the University of Florida, told Fort Myers News-Press.

Only California has experienced more cases in the U.S than Florida.

While there are significant differences in the filtration capabilities of cloth, surgical and N95 masks, all aid in preventing the transmission of coronavirus droplets to some degree, researchers say.

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On COVID-19 particle size

Dr. Amy Price, a research scientist at Stanford University who was involved in changes to World Health Organization mask guidelines, told Stanford Medicine that masks could impact how far viral particles can travel. The droplets that carry the viral particles are also larger in size than the virus itself, she noted.

“Many people argue that cloth masks can’t be effective because they can’t filter out viral particles, which are extremely tiny,” she said. “Most of these particles leave the mouth and nose in much larger droplets that become smaller through evaporation as they move away from the body. Trapping droplets with the mask means not nearly as many viral particles escape. So, when all parties in a gathering are wearing well-constructed, well-fitting masks, it provides an extra layer of safety for everyone.”

The COVID-19 particle is indeed around 0.1 microns in size, but it is always bonded to something larger.

“There is never a naked virus floating in the air or released by people,” said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech who specializes in airborne transmission of viruses.

“Breathing and talking generate particles around 1 micron in size, which will be collected by N95 respirator filters with very high efficiency,” said Lisa Brosseau, a retired professor of environmental and occupational health sciences who spent her career researching respiratory protection.

Surgical and cloth masks do not protect the wearer from COVID-19 particles as well as medical N95s. (The type of N95 masks used in construction are not effective against the novel coronavirus because they have valves.)

But the CDC does note, “A cloth face covering may not protect the wearer, but it may keep the wearer from spreading the virus to others.” By wearing a cloth covering in public, the spread of the virus can be slowed by lessening the transmission to others.

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Evidence shows masks help slow the spread of COVID-19

A study published in June in the Proceedings of the National Academy of Sciences by researchers from Texas A&M University, University of Texas, California Institute of Technology and University of California, San Diego found that masks were instrumental in lowering the number of infections in hot spots like Italy and New York.

“We conclude that wearing of face masks in public corresponds to the most effective means to prevent interhuman transmission, and this inexpensive practice, in conjunction with extensive testing, quarantine, and contact tracking, poses the most probable fighting opportunity to stop the COVID-19 pandemic, prior to the development of a vaccine,” the scientists wrote.

People wearing masks on July 18, 2020, in Charleston, South Carolina.

A study by University of Iowa researchers published in Health Affairs Journal in June found similar results.

“The study provides evidence that US states mandating the use of face masks in public had a greater decline in daily COVID-19 growth rates after issuing these mandates compared with states that did not issue mandates,” researchers wrote.

That study notes there is contention surrounding the recommended use of masks and concedes that a large-scale study has not been done, but cites asymptomatic cases as a strong reason to encourage face coverings.

"Because mask wearing by infected people can reduce transmission risk, and because of the high proportion of asymptomatic infected individuals and transmissions, there appears to be a strong case for the effectiveness of widespread use of face masks in reducing the spread of COVID-19. However, there is no direct evidence thus far on the magnitude of such effects, especially at a population level."

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Our ruling: False

While not all masks are 100% effective in stopping transmission of coronavirus droplets, studies show masks have been beneficial in slowing the spread of disease and have had a greater effect when comparing areas with and without mandates. The average COVID-19 particle may be smaller than drywall dust but is transmitted in droplets that are larger, allowing them to be caught by face coverings. We rate this claim as FALSE because it is not supported by our research.

Our fact-check sources:

Devan Patel is a public safety enterprise reporter for the Naples Daily News. Reach him at Devan.Patel@naplesnews.com or via Twitter at @DevanJPatel

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