Wildfires raise caution for outdoor activities
With its mild weather, fitness-minded population and ample trails for running, hiking and cycling, the Bay Area is one of the best places to exercise outdoors. But recent years have ushered in increasingly long and acute wildfire seasons, with fires from as far away as the Oregon border leading to poor air quality in the Bay Area — including the Spare the Air alert that started Wednesday.
So how should you think about the risks and benefits of exercising outdoors when the air is smoky? Is some exposure to smoke, in exchange for the physical and mental health benefits of moving your body outdoors, worth it?
The Chronicle interviewed five local experts — an immunologist, an air pollution researcher, a sports medicine doctor and two pulmonologists — on how they decide whether to exercise outdoors and what time limits or other adjustments to consider.
“It’s hard because there are clear benefits to exercising,” said Dr. Nick Kenyon, a critical care doctor at UC Davis Health who specializes in pulmonology. “Many people are used to exercising outdoors and want to continue to exercise outdoors. The best recommendation is to follow the Air Quality Index to get a sense of how bad it is.”
The Air Quality Index, or AQI, is the federal air quality measure that ranges from green (good), yellow (moderate), orange (unhealthy for sensitive groups), red (unhealthy), purple (very unhealthy) to maroon (hazardous) based on the concentration of air pollution, including fine particulate matter known as PM2.5.
In the short term, exposure to wildfire smoke is linked to higher rates of pneumonia, exacerbation of asthma and chronic obstructive pulmonary disease, airway inflammation and related infections, and other respiratory problems. Visits to emergency rooms for these conditions go up shortly after wildfire events.
In the long term, there aren’t many studies on the health impacts of exposure to wildfire smoke for the general population who aren’t firefighters. But research on particulate matter in other types of air pollution, like diesel and cigarette smoke, have found that chronic exposure to high concentrations of PM2.5 — which can get into the deepest parts of the lungs and into the bloodstream — is linked to higher risk of heart and lung disease. It can also weaken the body’s immune system by causing chronic inflammation throughout the body.
“That’s very much a concern for all of us,” Kenyon said. “Now that we’re exposed to wildfire smoke for a month, year after year, what are the cumulative effects? We’re worried about the development of lung diseases, which is asthma people don’t have before, and the development of cardiovascular disease.”
Experts generally agree that when the AQI is below 100 (green, 0-50; or yellow, 51-100), it’s safe to do rigorous outdoor exercise. They also agree that when AQI is 200 or above (purple, 201300; maroon, 301 and higher), people should not exercise outside, even if they’re healthy and can limit their time, because the potential damage to the heart and lungs from exposure to toxins isn’t worth it. Most think the cutoff should be 150, when the AQI reaches the red tier (151-200).
“Once it gets to red, purple or maroon …it’s really not safe,” said Dr. Michael Fredericson, a Stanford sports medicine doctor. “The potential negative outweighs the positive at that point.”
Where there’s more wiggle room for individual choice — depending on your health, age, appetite for risk, and duration and intensity of your workout — is in the 101-150 (orange) zone. Most experts say it’s probably OK for healthy adults to exercise outdoors under these circumstances. But sensitive groups, such as young children whose lungs are still developing, elderly people, and anyone with underlying respiratory or heart conditions, should avoid it. The following guidelines mostly apply to healthy adults who are considering exercising outdoors when AQI is in the orange zone.
Some experts are comfortable exercising outdoors when AQI is at the orange level. UCSF pulmonologist Dr. John Balmes, for instance, regularly runs, hikes, bikes and plays golf when air quality is in the yellow (moderate) tier, and continues doing so when it’s orange (unhealthy for sensitive groups) because he is healthy and doesn’t have chronic respiratory or cardiovascular disease. But he recommends thinking about less intense workouts, like a less strenuous hike instead of a run. He draws the line for vigorous exercise when AQI is above 150 (red).
“Over 151, the beginning of red, I wouldn’t advise doing exercises where you’re breathing through your mouth,” Balmes said. “Walking might be OK. But with running, cycling and heavy hiking, you’re going to breathe through your mouth so you bypass the filtering mechanism of your nose and you’ll get higher exposure. The nose is pretty good at filtering stuff out.”
Dr. Gina Solomon, who studies toxic chemicals and environmental health at the Public Health Institute, a nonprofit group that researches and advocates on public health issues, has done moderate exercise outdoors even when the air quality is poor — but only while wearing a well-fitting N95 mask. She doesn’t recommend doing so without an N95, which filters out most particulate matter including wildfire smoke.
“I have to confess I’ve been known to put on an N95 mask and take a walk even when air quality is pretty horrible,” she said. If you’re set on going outdoors when air quality is poor in your area, Solomon recommends checking the AQI on AirNow or California Smoke Spotter and heading to a nearby area where the air quality is better. During previous wildfire events, she drove from San Francisco to coastal Marin to take an outdoor walk.
“There are microclimates so you do wind up with differences, especially in the Bay Area,” Solomon said. Kenyon, of UC Davis, suggests working out at a different time of day. Ozone levels and AQI are sometimes better in the morning than in the afternoon.
If you decide to work out outside when AQI is orange, Fredericson, of Stanford, recommends limiting your time to 20 or 30 minutes. Studies have shown that when exposed to particulate matter in diesel exhaust, healthy young male cyclists who did a higher-intensity ride for 30 minutes had fewer markers of inflammation in their bloodstream than cyclists who rode at lower-intensity for longer periods of time.
Even though they were exposed to diesel exhaust, not wildfire smoke, Fredericson said the principle probably applies to wildfire smoke as well.
“You’re better off doing something more high-intensity for a shorter period than something low-intensity for a longer period,” he said.
Fredericson also recommends monitoring your heart rate to not go over 75% to 80% of your maximum heart rate. You can do that by wearing a device like an Apple Watch, or “a simpler way is to make sure you’re not gasping for breath,” he said.
Fredericson, who runs and swims outdoors, checks the AQI before heading out for a workout. He also pays attention to how he feels, like if his eyes are watering, he’s coughing or his throat feels irritated.
“Looking at those AQI values is helpful because potentially you might tolerate something better than other people,” he said. “But you’re still getting exposure to that particulate matter that can do damage long term and it might take a while before you realize it.”
Afterward, drink extra water to help flush out toxins and keep mucus membranes moist, and eat antioxidant-rich foods like leafy greens, berries and fish oil, he said.
Those who can’t avoid exposure — such as professional athletes who practice outdoors, or people who work outdoors — can take precautions before and after, said Dr. Tina Sindher, a Stanford immunologist and allergist who treats patients with asthma.
“If they have asthma, be mindful this will be an asthma trigger. Do things ahead of time to maximize lung function with (inhaler asthma medication) albuterol, make sure your medications are up to date, do a follow-up checkup soon after exposure with your primary care doctor,” she said. “Tee your body up for success if you can’t avoid the exposure.”
If you move your workout indoors, close the windows, put your air conditioning on recirculate mode, and use an air cleaner or air purifier with a HEPA filter.