Can cloth masks keep us safe? Hamilton researchers studied data over a century

While there is still no direct clinical evidence that proves exactly how protective homemade masks are, one recent literature review from Hamliton researchers suggests they may help more than they will hurt.

Hamilton Public Health and researchers say masks — even ones made at home — may protect people

A literature review from Hamilton researchers suggests homemade masks could be useful against COVID-19. (Andrew Vaughan/The Canadian Press)

As Hamilton moves toward a new "post-peak" normal of living with COVID-19, public health officials say wearing masks in the community will be one of the most important ways to protect against the spread of the virus.

Dr. Elizabeth Richardson, Hamilton's medical officer of health, said homemade cloth masks might even be enough.

"If we have a mask that's about 60 per cent effective and 60 per cent of people are wearing them, it looks like that's enough to control the pandemic, to get to the point where it's not just continuing on but starts to die off as we go forward," she explained to city council on Wednesday morning.

While there is still no clinical trial that proves exactly how protective the masks are, one recent literature review from Hamilton researchers suggests they may help more than they will hurt.

"The cloth is really quite good," Catherine Clase, an associate professor of medicine at McMaster University and a nephrologist of St. Joseph's Healthcare Hamilton, said.

"The point is not that some particles can penetrate the mask, but that some particles are stopped, particularly outwardly, from the wearer," said Clase in a release about the research.

"We acknowledge we don't have the clinical evidence, we don't know whether it reduces transmission or illness, but given the pandemic is difficult to control, it is likely to be a good intervention."

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She and her team looked through a century of research on cloth masks to find out how effective they have been in the past.

Some of the articles dated back to the Spanish Flu, which hit Canada between 1918 and 1920, while others looked at health-care workers and surgeons in the 60s and 70s. 

Clase said the results surprised her. While there's no perfect face covering, masks with a layer of flannel sandwiched between muslin were extremely effective. Cotton was also found to be a strong material. Multiple layers of cloth seem to even be enough.

"It's not intuitively obvious cloth is going to block aerosol particles, when you hold cloth up to the light, you can see the holes through it, but several layers of cloth will reduce a proportion of particles, even aerosol particles," she explained.

"Anybody who is making a cloth mask, particularly if it is a multi-layer mask, is probably doing a good thing."

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Clase noted people with respiratory problems and anyone under the age of two should not wear a mask.

The researchers acknowledge the lack of direct evidence is a factor in the sometimes conflicting messages from Canadian public health officials on use of masks.

She also emphasized the masks alone won't be as effective without physical distancing and proper handwashing.

"We don't know for sure whether masks are going to protect the wearer, we don't know for sure whether it's going to protect other people, but if people are wearing it out of kindness and altruism, I think that's a great spirit of togetherness we can have," Clase said.

"That kindness, that willingness to try something in case it helps somebody else, that's really the best we can be in this pandemic."


Bobby Hristova is a journalist with CBC Hamilton. He reports on all issues, but has a knack for stories that hold people accountable, stories that focus on social issues and investigative journalism. He previously worked for the National Post and CityNews in Toronto. You can contact him at bobby.hristova@cbc.ca.