You’re ready to swap your old cloth masks for N95s as some experts recommend, but the higher price tag and two little words – “single use” – are giving you pause. How long can you really wear an N95 and still protect yourself and others from Covid-19 risk? “I wear mine for a week,” said Linsey Marr, a professor of civil and environmental engineering at Virginia Tech. An N95 mask’s material and filtration ability aren’t “going to degrade unless you physically rub it or poke holes in it,” Marr said. “You’d have to be in really polluted air … for several days before it lost its ability to filter out particles. So, you can really wear them for a long time. “People have been talking about 40 hours – I think that’s fine. Really, it’s going to get gross from your face or the straps will get too loose or maybe break before you’re going to lose filtration ability,” she added. The reason why N95 masks are designated as single use is because they’re categorized as medical masks, said Erin Bromage, an associate professor of biology at the University of Massachusetts Dartmouth. In medical settings, health care workers change masks more frequently to avoid “cross-contaminating a patient room with equipment that was worn in a room of an infectious person and then moving to the next room and bringing that infection with you,” he said. “When you then take a medical-grade thing that’s single-use and put it in the general public, we’re not worried about you cross-contaminating different environments you’re being in. It’s really about providing protection to you.” N95s “used to be only $1 or so each,” Bromage added, but prices have recently spiked as public demand for these masks has increased amid Omicron variant concerns. If you safely reuse N95s, you’re getting at least two or three days of use from one mask, Bromage added, but “I realize that it still adds up to an expense.” Some local public health departments, such as the Maryland and Milwaukee health departments, are offering free N95 masks. Here’s what else you should know about safely wearing and reusing N95 masks. Why N95s? Compared to cloth masks, properly fitted N95s better prevent tiny particles from getting into your nose or mouth thanks to certain materials – such as polypropylene fibers – acting as both mechanical and electrostatic barriers to shared air, the primary driver of coronavirus infection. The difference between N95 and KN95 masks is where the mask is certified, according to Oklahoma’s state health department. The US certifies N95s, whereas China approves KN95s. Around 60% of KN95 respirators sold in the US are counterfeit and don’t meet the requirements of the National Institute for Occupational Health & Safety, according to the US Centers for Disease Control and Prevention. “If they’re made to the standard and certified by the appropriate boards in their country like NIOSH here, they all do basically the same thing,” Bromage previously told CNN. “But there is a ton of knockoffs that are not certified in the KN95 side of things, that may meet the standards but they’re not certified to meet it. And there’s others that clearly don’t.” N95 masks “are not made for kids,” Marr said. “For larger kids, my 10-year-old wears an N95 that comes in a small size (intended for adults).” “If you see an N95 as marketed for children, that should raise a red flag,” Marr added. “There will be KN95 and KF94s that are designed for and marketed for children. With those, it’s the same issue as we discussed for adults, which is to make sure you’re getting them from a trusted, reputable source, because there’s a problem with fake KN95s that are not nearly as protective as they should be.” Project N95, the National Clearinghouse working to provide equitable access to personal protective equipment and coronavirus tests, is a reputable source for N95 and KN95 masks, Marr said. KF94s are Korean-standard masks. “Certainly, for children, a KN95 or KF94 will provide better protection on average than a surgical mask or cloth mask,” Marr said. You might have to try a few different brands or shapes of KN95s, KF94s or small N95s to find one that fits well and is comfortable for your child, Marr said. If you still have trouble fitting the mask to your child’s face, you can tie the ear loops or use toggles or cord lock adjusters to ensure the mask fits tightly enough, she suggested. This CDC video on the knot and tuck method might also help. Reusing an N95 mask – and when not to To reuse N95 masks as safely as possible, avoid touching the front outer part of the mask when putting it on, Marr said. Instead, try to handle it by the edges or straps. “Definitely avoid the part right in front of where you breathe, like right in front of your nose and mouth,” she added. Even after wearing an N95 in a crowded indoor setting – such as a subway – Marr said “these masks are really designed to handle a lot of particles and will continue to work.” However, a known exposure should affect your approach. If “I was working in an office and I was wearing an N95 and someone in my office had tested positive, I’d know I was well-protected,” Bromage said. “But I’d probably throw out that mask. Because that mask has done its job of trapping the virus and I don’t even want to take the risk of it being there and getting on my hands or whatever.” That you could have unknowingly been near an infected person in any other public space – such as a subway or grocery store – while wearing an N95 mask is possible. Staying at least 6 feet away from others as much as possible can help reduce Covid-19 risk. If the mask becomes damp, visibly dirty, bent, creased or otherwise damaged – including from wearing makeup – you need to replace it since these conditions could decrease the mask’s effectiveness, Marr and Bromage said. “The longer you wear it, the more it’s actually trapping material – which means that the breathability, the resistance of the mask, starts to decrease,” Bromage said. “One of the first indicators of being able to change it if it looks nice and clean is that it just feels a little harder to breathe through. There appears to be more resistance with every breath.” How to sanitize N95 masks The longer and more frequently you wear an N95 mask, the more contaminated it can become. But particles will die off over the course of a few to several hours, Marr said, and even faster if you set the face covering aside in sunlight. “Things like temperature and sunlight have an effect, but you don’t want to be throwing it in an oven or microwave,” Bromage said. “I used to stick mine on the dashboard of my car in summer, and that would do more than enough in regards to the heat and the direct light that it was getting. But in reality, there’s nothing you can really do to extend its life through cleaning that is accessible to an average person.” Because N95 masks have that special static charge that helps filter out viruses, you shouldn’t wash the masks, as water will dissipate the charge, Marr said. Overall, the contamination risk in reusing N95 masks is “lower, much lower, than the risk of you not wearing an N95 and breathing in particles,” Marr said. “I don’t want people to avoid wearing an N95 because they’re worried about contamination on an N95. The N95 is going to provide a major net benefit.” This story has been updated with additional detail about children’s masks.