if your n95 mask has a valve, you could be spreading covid-19

this story was originally published on april 1 and has been updated on july 22 to include information about n95 masks with valves.the message to canadians over the last few weeks has changed: wear face masks.dr. theresa tam, canada’s chief public health officer, advised that non-medical masks help prevent the spread of covid-19 by people who don’t know they have it.the most effective masks — n95s — are in such short supply that dr. tam said in another briefing that officials are looking at whether or not they can be disinfected and reused for frontline health workers.yet masks of varying kinds have been declared mandatory for the general public by the governments of austria, the czech republic and slovakia. and in many parts of asia there is social pressure to wear them.“in asia, it’s more like a civic duty for people. people who don’t wear face masks are criticized,” says dr. elaine shuo feng, an epidemiologist and statistician at the oxford vaccine group in the u.k. who authored a paper on the rational use of face masks in the lancet last week. “in hong kong, face masks are recommended for anyone who uses public transportation or goes to crowded areas.”so which mask should you use? here’s a shorthand to the options — and how effective they are.

n95 respirators: the gold standard for health workers

first things first: n95 is a designation, meaning they are approved for medical use by health canada. masks with that name, in varied shapes including cups, flatfold or duckbill, must be able to filter out at least 95 per cent of very small particles.to do that, n95s require fabric with pores no more than 0.3 microns in diameter, or 300 nanometres. manufacturers use what’s called “melt-blown” fabric made from interlaced polypropylene fibres (think a cotton candy maze trapping particles as they travel) that are notoriously hard to produce.however, all this hard work goes to waste if the mask is not fitted properly. n95 wearers often have to remove any jewellery and facial hair, and healthcare workers are fit-tested for n95 respirators before actually using them to make sure they are completely sealed against their faces — otherwise, viruses will still sneak in the sides. during fit tests, sweet or bitter solutions are sprayed to see if the wearer can taste them.health canada also notes that “both respirators and masks need to be used in combination with appropriate eye protection (e.g., face shield, goggles) to achieve full protection of the eyes, nose and mouth.”should you see n95s for sale, also note that they have a “best before date.” reuters recently reported on the millions of masks ontario had stockpiled — but were now expired.lastly, not all n95 masks are created equal. masks with exhalation valves are not recommended for covid-19. n95s with valves are designed for construction workers to prevent dust and other particles from getting in, but it does not prevent an infected person from spreading droplets. masks with valves have good filtration for air coming in because they’re one-way and does not allow air in through the valve — outside air is forced to go through the mask itself (the filter). but the valve opens up when the user breathes out, which makes it easier for the user to breathe, but it doesn’t prevent their droplets from transmitting to others around them. in san francisco, masks with valves have been banned because it doesn’t stop source control and puts others at risk.

 

surgical masks: the next best thing

in many east asian countries, these loose-fitting face masks — made from fabric or polypropylene — have been in widespread use for many years. they offer protection against 80 per cent of tiny particles, and block out air pollution. given the challenges of fitting medical-grade face masks, a 2016 cmaj review found they were nearly as effective as n95s. (they are also a convenient way to mask identity; google any photo of the hong kong protests last year.)although surgical masks are not designed protect the wearer — they are made to protect patients from any droplet contamination from a doctor during surgery — they are being used as a contingency tool even in hospitals. troubling for many healthcare workers, that means reusing masks that are meant for single use.as of march 31, the canadian government had dedicated $2 billion to producing surgical masks in canada (as well as face shields, gowns, ventilators, test kits and swabs).

homemade: a last (and sustainable) resort

there is not a lot of evidence about the effectiveness of homemade masks. in a small 2013 study, researchers found masks made from cotton t-shirts (which had been tested to fit properly) were better than no protection but “should only be considered as a last resort.”that last resort has arrived in many jurisdictions, however: in toronto, michael garron hospital has made a plea for donations of as many as 1,000 homemade masks — every week. they even uploaded a simple face mask sewing pattern that can made from bedsheets, t-shirts, or tea towels.you’ll need elastics and a sewing machine for that pattern, but the new york times has also posted a pattern that can be hand-sewn.can’t sew? unfortunately, there’s no substitute for an n95 with any home-sourced material, says dr. jason kindrachuk, a medical microbiologist and the canada research chair in molecular pathogenesis of emerging and re-emerging viruses at the university of manitoba.masks have tiny pores that can capture viruses and keep any particles bigger than the pores out, says kindrachuk. but anything smaller passes through. the material scarves are made of are not effective. even if you stacked multiple scarves, the pores are still not small enough, and viruses can still pass through.“there is precedent for using things like cloth masks or tea cloths for making homemade masks,” he says. “at the end of the day, those types of homemade products work better than nothing but they are much less effective than surgical masks or n95s.”

the downside of face masks

no mask will be perfect against the virus. coronavirus particles are actually smaller than the regulation pores of even n95 masks.masks can also lead to a sense of “false security,” said canada’s top doctor, chief public health officer dr. theresa tam in a media briefing march 30th. you may be touching your face more. (never touch the front of the mask.)feng adds that many people wear a mask with their nose or even mouth exposed, rendering it completely useless.a dirty mask might even become the source of an infection. “when someone gets home, how are they taking the mask off without touching their face? how are they ultimately disinfecting them and sanitizing them?” says kindrachuk.there’s also the potential this virus can be transmitted through the eyes. “how much false security do you give to people by having them use masks? unless they’re physical distancing, there is still the potential for transmission even though the mouth and the nose are covered.”

the bottom line

for all of their flaws, masks are a useful tool to prevent infection — if combined with staying at home, physical distancing, and washing your hands with soap.no matter what type, masks are not a catch-all, says kindrachuk. he stresses that physical distancing is still the absolute primary point the general population needs to be doing — since healthcare workers can’t.“i don’t think one single policy is effective during this outbreak. we should combine all the public health measures and consider the rational use of the masks, if possible,” says feng.“stay at home as much as possible and do your best with physical distancing because these are more important. if you have to go outside and talk and interact with other people, i think it would be helpful to wear a face mask.”any companies that have n95 masks can donate them to health canada at hc.mdel.application.leim.sc@canada.cadiana duong is a writer and editor at healthing. follow her on twitter @dianaduo.dduong@postmedia.comdon’t miss the latest on covid-19, reopening and life. subscribe to healthing’s daily newsletter covid life