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What science says about masks

Multiple studies show how well different types of masks can block both big and small particles that can carry the SARS-COV-2 virus.

MINNEAPOLIS — Facemasks have become a potent political statement in the U.S., like a scarlet letter showing how you voted in recent elections. 

But mask use is not political dogma, it’s science, and an imperfect one at that.

After reading through most available studies on the efficacy of masks and interviews with several top medical and infectious disease experts, the question really isn’t ‘Do masks work?’ but rather, ‘Which ones work the best?’

Below, you will find multiple studies that show how well different types of masks can block both big and small particles that can carry the SARS-COV-2 virus. The results vary widely based on material and how the mask is worn.

“In the end, there won't be any blue states or blue counties, red states or red counties,” said Dr. Michael Osterholm, infectious disease expert at the University of Minnesota Center for Infectious Disease Research and Policy. “They will all be COVID colored. And that's what we are seeing.”

Osterholm has taken heat for questioning how well homemade masks work against the virus. He talks about the latest available evidence for and against the efficacy of masks regularly in his weekly podcasts.

He made it clear to us he was not anti-mask.

“I'm not only not anti-mask, I'm saying wear it. I wear one. I owe it to the public to tell them what I know and don't know. This is where it has been very hard because in public health nothing is necessarily yes or no. It's not right or left,” said Osterholm.

Full interview with Dr. Michael Osterholm:

The problem with a 'perfect' answer on masks

Here's the hiccup preventing a perfect answer on masks.

Osterholm says when we sneeze, cough, sing, or talk, larger-sized droplets come out of our mouths (>5 microns), potentially carrying a bunch of virus with them. He calls those "boulders."

And when we simply breathe, much smaller, microscopic particles about the size of the virus (.1 micron) come out as well. He says think of these as "marbles."

Recently, 239 scientists sent a letter to all public health departments worldwide saying enough studies have "demonstrated beyond any reasonable doubt that viruses are released during exhalation," or just breathing.

So, the big question here: do homemade masks block the "boulders" and the "marbles?"

“In terms of masks, I'm saying we have a growing amount of evidence that masks reduce risk,” said Dr. Sheree Schwartz, an infectious disease epidemiologist at Johns Hopkins University.

She says not all homemade masks are equal. And while evidence shows they can work, there's a lot of complexity to how well they work.

“How many layers does that mask have? How tight is it to your face? What are the openings? All of those things are going to matter,” said Schwartz.

Florida Atlantic University study

This study from Florida Atlantic University shows us through lasers how effective masks can be.

A normal cough with no mask projected droplets up to 12 feet, remaining in the air for minutes.

Folded bandanas and folded cotton handkerchiefs stopped up to half the distance of smaller droplets in the cough, but proved least effective.

Two layers of stitched quilting-cotton cut the distance of the droplets in the cough to 3 inches but also had droplet leakage on the sides.

It still performed better in this case than a store bought, cone shaped mask.

“If everybody wore a mask, I think we could beat the pandemic pretty quickly,” said Dr. Manhar Dhanak, professor of fluid mechanics at Florida Atlantic University who helped conduct the study.  

A more in-depth look at mask fabrics

Another study, used by the CDC and published in American Chemical Society, used a machine to run simulated breathing through different mask materials.

Here's what it found:

Cotton is a great filter, but it depends on the quality.

Two layers of low thread count cotton, like in t-shirts, allowed more than half of big and small particles to pass through.

But high, 600-thread count cotton, like those expensive bed sheets, blocked out 99.5% of the "boulders" and 82% of "marbles."

This study claims the absolute best of homemade masks are a hybrid of high thread count cotton with four layers of silk in between. The mask blocked out 98% of big droplets and 94% of smaller ones.

But there’s a caveat, and it’s a point Dr. Osterholm has made for some time: none of this data rings true if you aren't wearing your mask correctly.

The study took that same exact high performing hybrid mask but allowed for some gaps or leakage on the sides.

In that scenario, the mask blocked only roughly 35% of all particles.

“I would say I agree that masks are not a silver bullet. This one intervention isn't a perfect solution, but it is one of several tools that we have that if used in combination can have a really substantial impact on the epidemic,” said Schwartz.

Epidemiological studies show masks can be effective   

Another study, published in The Lancet and commissioned by the World Health Organization, conducted a meta-analysis of 172 studies on SARS-COV-2, and SARS and MERS.

While none of the studies examined the effectiveness of homemade masks, the meta-analysis claims N-95 rated masks reduce the odds of infection for all three viruses by 96%. The analysis showed surgical masks (or 12-14 layer cotton equivalent) reduced the odds of infection by 67%.

One common critique of this review is only seven of the studies examined SARS-COV-2 and only two of the studies were in a community setting.

Another study from the Annals of Internal Medicine shows the importance of mask wearing, among other precautions, for people who don’t feel any symptoms.

It showed asymptomatic people appear to account for about 40 to 45% of SARS-COV-2 infections, and it claims they can transmit the virus, without symptoms, for potentially longer than two weeks.

This epidemiological study from China traced back 41 pre-symptomatic COVID-19 carriers who returned to their homes after visiting Wuhan in January.

According to the study, those 41 people had close contact with 197 people.

Pre-symptomatic people who wore a mask spread the virus to 8.1% of people in close contact.

Pre-symptomatic folks who did not wear a mask spread the virus to 19% of people they had close contact with.

You can read more studies for yourself and find out what experts have to say about the quality of those studies at the Johns Hopkins Novel Coronavirus Research Compendium.

RELATED: Where are face masks required in Minnesota?

RELATED: Coronavirus under control in 8 weeks if everyone wears masks, CDC director says

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The state of Minnesota has set up a data portal online at mn.gov/covid19.