Updated 8 a.m. on January 9, 2025
Californians have become familiar with masks in recent years.
First we learned about the power of N95 and N100 masks to protect ourselves from wildfire smoke. And during the COVID pandemic, masks of all kinds became a part of our daily wardrobe.
When COVID levels rise in Bay Area wastewater, many people choose to put those masks back on in crowded indoor spaces like the grocery store or rush-hour BART. But as wildfires continue to threaten California — most recently with the devastating fires in Los Angeles County that have claimed at least five lives, prompted mass evacuations and destroyed homes and landmarks across the region —just what should you cover your nose and mouth with if wildfire smoke and COVID collide again?
The short answer is: That collection of N95 or KN95 masks you may still have in your home is the best choice for protecting yourself against both COVID and wildfire smoke.
Keep reading for what you need to know about masking for different reasons in 2024.
“The best mask for protecting oneself from wildfire smoke is an N95. That’s also the best mask for protecting oneself from coronavirus,” UCSF pulmonologist and professor of medicine Dr. John Balmes said.
The Centers for Disease Control and Prevention (CDC) say that well-fitting respirators that are approved by the National Institute for Occupational Safety & Health (NIOSH), like N95s, offer you the “best” kind of protection against hazards in the air, including the droplets that spread COVID. (A note that you’ll usually see the CDC officially using the word “respirator” to refer to these kinds of face coverings that are highly effective against particles, and “masks” to refer to the types of face coverings that are less effective, like cloth masks and surgical masks — more on those below.)
The “95” in N95 also indicates that these respirators “achieve a minimum of 95% filtration efficiency” against dangerous particles, according to the CDC. Read more about how N95 masks work and why they’re so effective.
A caveat: Some public health officials say N95s aren’t for everyone, because of the potential for user error when it comes to fit — and for causing the kind of discomfort that makes some folks less likely to wear them consistently.
Veronica Vien, a public information officer for the San Francisco Department of Public Health, said masks like N95 can be uncomfortable to wear for long periods of time and must “provide a tight seal around the wearer’s mouth and nose” to work effectively. “If an N95 respirator makes you feel better, wear it. If you feel worse, please don’t,” Vien said.
UCSF’s Balmes also said some types of KN95 masks, which are similar to N95 masks, but made in China, are also good. The CDC calls these kinds of masks “International filtering facepiece respirator,” because they are tested to international standards and not NIOSH standards, meaning they “may not have the rigorous quality assurance requirements meeting those [masks] that are NIOSH Approved.”
These types of face coverings work well for wildfire smoke, but are less effective at stopping the spread of diseases like COVID — even with tape over the valve.
That’s because while these valves stop particles from reaching your mouth, they can allow you to breathe air out of your mask without filtering it. So if you have COVID, you’ll be breathing infectious particles out at others through those valves in a way that a no-valves N95 doesn’t permit.
Surgical masks are “actually somewhat protective with regard to wildfire smoke because they’re standardized,” Balmes said. He estimated surgical masks can reduce exposure to wildfire smoke by roughly 20%.
As for COVID, the CDC says that “well-fitting disposable surgical masks” are only the second-best mask to protect yourself from the virus, along with KN95s — behind N95 masks.
Wearing a cloth mask was one of the primary ways people tried to limit the spread of the virus in the earliest days of the pandemic. But at this stage, the CDC has advised that while these kinds of masks “may block droplets,” they don’t protect against small particles — so they’re not a good choice to protect against COVID.
And a cloth mask doesn’t filter out wildfire smoke. As the CDC notes, neither cloth masks nor surgical masks “have the type of filter media that will filter out the smoke particle”.
While masks are a good option, public health officials say the most effective way to keep yourself safe from wildfire smoke is to stay inside as much as you can.
Below is an interactive, crowdsourced air quality map from the private company PurpleAir. Read more information on air quality and how it’s measured.
This advice to stay indoors may not feel particularly helpful or possible during a heat wave, or with impending evacuation orders if you live in an area directly affected by wildfires. The Bay Area Air Quality Management District recommends that “when wildfires are affecting air quality, staying indoors with windows and doors shut is the best way to protect your health”, if heat allows:
On June 17, 2024, the Air District launched an air quality incident notification system. You can now sign up to receive notifications about incidents impacting air quality for any (or all) of the Bay Area’s nine counties. You can choose to receive notifications via email, SMS text or both.
The California Air Resources Board (CARB) also recommends mechanical air cleaners with a high efficiency particulate air (HEPA) filter that collects very small particles and does not emit harmful substances. These air cleaners can dramatically reduce indoor particle levels, in some cases by more than 90%. See a list of CARB-certified air cleaning devices.
If you don’t have air conditioning — which makes closing doors and windows especially difficult during a heat wave — consider getting some battery-operated fans and reducing activities that increase indoor air pollution, like burning candles, cooking on gas stoves or vacuuming. We also have instructions on how to make your own low-cost air purifier.
An earlier version of this story was originally published on Aug. 21, 2020.
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