As smoke billows into cities such as San Francisco and Oakland from multiple wildfires, the air is no longer safe to breathe outside. But because of the pandemic, the N95 masks that public health experts recommend for protection aren’t available to buy. Can the cloth masks that you’re already wearing help filter the smoke?

Probably not. Cloth masks were first recommended to help slow the spread of COVID-19 because they stop droplets coming out of your mouth from infecting others, rather than because they filter what’s coming into your mouth. (Though further study has found that your own mask does protect you from others a little, because wearing a mask can reduce the “dose” of the virus, meaning that the wearer might get less sick.) “[A cloth mask] is more of an outward protection rather than an inward protection,” says Albert Rizzo, chief medical officer for the American Lung Association. “So having said that, that’s exactly the opposite of what wildfire masks are designed to do. You want to try to protect yourself from inhaling the particles as a result of a wildfire. Unfortunately, those particles are small enough that facial coverings are not designed to be protective at that level as compared to an N95.” The CDC makes the same point, saying that cloth masks offer little protection against smoke.

The shortage of N95 masks is still a problem for doctors and nurses treating COVID patients, and that means that the masks aren’t available now as wildfires dramatically increase in California and other locations. As of August 19, 367 fires were burning in California. N95 masks can block 95% of tiny particles as small as 0.3 microns; that’s enough to catch most of the dangerous particles found in smoke. “We’ve been hearing all along, save those for the frontline workers because they’re scarce,” says Rizzo. “But now we have another reason that they need to be used, in a wildfire situation.”

Wildfire smoke can cause health problems, particularly in people with underlying conditions such as asthma. The CDC warns that because smoke from fires can irritate and inflame the lungs, it can also put people at greater risk of getting sick from COVID-19. (The fact that some people have to evacuate and stay in shelters with others who may have the virus doesn’t help.) People don’t have good options now, Rizzo says, other than to try to stay inside with the windows closed or stay away from the smokiest areas.

Still, it’s possible that some non-N95 masks may help more than others. A surgical mask, made from similar material, might help if it’s hacked to fit as tightly as possible. Some fabrics can filter out virus particles more effectively than other fabrics, and they might also give a little more protection than something loosely woven. But there’s also a clear argument that more masks should have been available to begin with, and companies need to ramp up production of N95 masks even more than they already are. 3M alone plans to produce more than a billion masks by the end of the year, but we still don’t have enough yet.