Wildfire smoke contains a complex mix of gases, hazardous air pollutants, water vapor and particulate matter (or particle pollution), which pose the greatest threat.
Some of those particles, including dust, dirt, soot or smoke, are so large or dark that they can be seen with the naked eye. But the tiniest of them — microscopic particles that are about one-fifth to one-thirtieth as wide as a human hair — can travel deep into your lungs and even into your bloodstream. There, they can cause inflammation and dampen your immune system.
While ash and soot from burning wood are some of the most concerning types of particle pollution, wildfire smoke can also contain other toxic and cancer-causing substances, including chemicals, heavy metals and plastics. Indeed, said Dr. John Balmes, a pulmonologist and professor of medicine at the University of California, San Francisco: Smoke from fires is “pretty much like tobacco smoke without the nicotine.”
Breathing in wildfire smoke can make anyone cough, wheeze and struggle for air. It can irritate your eyes, nose and throat, and cause headaches.
Those with certain conditions like asthma, chronic obstructive pulmonary disease or heart disease are especially vulnerable, as are those who are very young, very old or who are pregnant. Even short-term exposures may have long consequences: One 2021 study, performed in California, concluded that just one week of exposure to wildfire smoke was associated with a 3 percent increase in premature births.
Lower income regions and communities of color may also be at greater risk of health threats from wildfire smoke, since they are more likely to breathe in daily pollution from cars, trucks and power plants, said Keith Bein, an atmospheric scientist at the Air Quality Research Center at the University of California, Davis. “It puts you behind when a wildfire comes,” he said, adding that simultaneous exposure to smoke and smog is an environmental justice issue that “adds insult to injury.”
If a wildfire is close enough that you can see flames or if your community is blanketed in smoke and ash, you should be prepared to evacuate if you’re instructed to do so, according to the Environmental Protection Agency.
Even if you’re far from flames, but the smoke is darkening your skies, your safest choice may be to leave, Dr. Prunicki said. If that’s not feasible, the likely next best thing is to stay inside and take steps to limit your smoke exposure.
According to the E.P.A., vulnerable people like older adults, children and those with heart or lung conditions should avoid going outside when the air quality index — a numerical value from 0 to 500 that indicates air pollution and health risk levels — goes over 100. Anything over 150 means it’s unhealthy for anyone to be outside without a high-quality mask.
You can consult AirNow’s interactive fire and smoke map, a federally-run tracker for air quality conditions. PurpleAir can also offer a more local picture of air quality, as can other products and apps, like IQAir and BreezoMeter.
For children, safety concerns arise when the air quality index is even lower. Because breathing smoke can increase the risk of asthma in children and might even have irreversible consequences for their immune cells, experts recommend that, when the air quality index is above 50, caregivers should start thinking about keeping children inside, especially if they already have asthma.
That’s not always easy. Public health experts acknowledge that parents must give children space to move around. So one trade-off “is to have the kid wear a mask outside,” Dr. Balmes said. But keep in mind that dust masks, surgical masks and bandannas won’t be enough to protect your child from smoke, according to the Centers for Disease Control and Prevention. And higher quality masks, like N95s, typically only come in adult sizes, so children may not be fully protected when wearing them. In all cases, outdoor playtime should be limited.
By some estimates, a good air filtration system can cut smoke pollution indoors by about 50 to 80 percent. When skies grow hazy, if you have central air and heating, close your windows and switch your system’s filtration settings to recirculate. Adding a higher efficiency filter, like one with at least a Minimum Efficiency Reporting Value (MERV) 13 rating, to central air systems makes them even more effective at removing small particles from smoke. If you don’t have central air, portable air purifiers with HEPA filters can work well in smaller spaces.
Experts caution that you should avoid using air purifiers that rely on and emit ozone, which can be harmful even at low levels and can irritate the lungs. Check with your local public agencies to see if they provide guidance or financial support for buying air filters. Low-income people with certain respiratory conditions who live in the Bay Area, for instance, are eligible for free portable air filters.
If you can’t find an affordable air purifier, you can make one out of a box fan, some tape and some high efficiency filters.
Thick smoke can sneak into your home through loose seals and cracks; closing those up can help. Simply shutting windows can cut pollution by about 30 percent. If it still smells like a barbecue inside on a smoky day, placing wet towels around cracks under doors and around windows can slow smoke’s entry into your home.
The E.P.A. also recommends avoiding activities like cooking, vacuuming or smoking on smoky days, which can stir up pollutants already inside your home. And the American Lung Association recommends using a good welcome mat to wipe your shoes on, or taking shoes off altogether when you’re walking around inside your house, to avoid tracking in contaminants.
If your indoor space is larger than an air purifier can filter, the E.P.A. recommends dedicating one room as a “clean room” to use as a refuge on smokier days. But avoid using rooms where you create smoke or other particles indoors, like the kitchen, or any room with a lot of windows and doors.
Health experts say that it might. Air pollution can cause stress and inflammation in your brain as it fights off invading particles, according to Dr. Robin Cooper, an associate clinical professor of psychiatry at the University of California, San Francisco. And that can compromise executive functioning, or the cognitive skills that help direct your choices, including working memory and self-control, she added.
“It interferes with your ability to think clearly,” Dr. Cooper said. “Headaches are a part of that.”
Direct exposure to a wildfire can raise your risk for certain mental health conditions, including post-traumatic stress disorder and depression. And there’s some preliminary evidence to suggest that some people may also have heightened anxiety, fear and stress during or following an exposure.
Dr. Cooper, who has been in private practice for more than 40 years, said that she has seen elevated anxiety among her patients who have dealt with wildfire smoke in the past. One mother in the Bay Area, she remembered, was so concerned about being able to protect her child from wildfire smoke that she worried that she shouldn’t have become a parent at all.
But making sure you’re prepared for the hazards of wildfire smoke before a fire occurs can help, Dr. Cooper said. That may include setting aside good N95 masks for smoky days, gathering supplies like bottled water, nonperishable food, personal hygiene products and flash lights if you have to hunker down indoors, or having a “go-bag” ready if you need to evacuate.
Not to mention, Dr. Cooper added, talking with your friends and neighbors about how you’re feeling about climate change and how to prepare for smoke when it comes. “Collective engagement with other people diminishes a sense of isolation,” she said. “It builds resilience.”
Limiting your time outside is a good start. There is no safe distance from smoke, and its health effects can accumulate. So if you must go outdoors, wearing a high quality mask, such as an N95 respirator, is essential.
Reporters at Wirecutter, a New York Times Company that reviews and recommends products, suggest choosing a mask that filters exhalations as well as inhalation air. You want to check to make sure the mask has a good seal around your nose and mouth. Cloth masks are less effective.
And keep in mind that no mask will protect you 100 percent. “Wearing an N95 reduces your exposure, but if you have to go out, you will get exposed,” Dr. Balmes said.
There’s also some evidence that you may want to protect your skin when you go outside. In a first-of-its-kind study published in 2021, researchers found associations between short term smoke exposure and health care visits for itchy skin and eczema.
Some skin care creams and products with labels like “antipollution” or “pollution protection” probably won’t help much. Though applying a lotion with emollient properties — like shea butter, lanolin or petroleum jelly — before you go outside may help create an artificial barrier on your skin. Dermatologists advise that you avoid smoke if you can, cover up with long sleeves and pants if you have to go outside, and cleanse your skin after spending time outdoors to remove any pollutants.