The air the you inhale shapes your health, exercise safety, and endurance potential
I’m writing this from an unfamiliar place. The wildfires sweeping through California forced me to evacuate my home in Los Angeles. I’m thankful to be safe. It’s been a strange and unsettling time. Daily life has been turned upside down—normal routines disrupted, my community fractured, and a tragic sense of loss and desperation in the air.
And yet, despite the chaos, I’ve found myself still seeking moments of relief. The familiar rhythm of movement—whether a walk or a run—feels grounding in a time when everything else is uncertain. But even then, there’s the lingering question: Is it safe to be outside when the air feels heavy with smoke?
For many of us, running is a lifeline. An escape. It’s how we clear our heads and reclaim some normalcy. But in moments like these, what’s in the air we breathe can no longer be ignored.
Is It Safe to Exercise Outdoors When Air Quality Is Poor?
The first concern for any runner or outdoor exerciser should be safety. The Air Quality Index (AQI) is a helpful tool for determining whether it’s safe to be outside. The AQI ranges from Green (Good) to Maroon (Hazardous), with each tier representing progressively worse air quality. Understanding these levels can help runners make informed decisions about when to exercise outdoors and when to stay inside. Here’s a quick breakdown of AQI levels and what they mean for outdoor activity:
(Photo: American College of Sports Medicine)
Most healthy individuals can safely exercise outdoors in Orange conditions for 30 to 60 minutes. However, once the AQI hits Red or higher, it’s best to move your workout indoors to avoid potential health risks. Prolonged exposure to polluted air can cause respiratory irritation, fatigue, and reduced performance, particularly during endurance activities.
Timing your run wisely is another key factor. While we often run early in the morning or late at night to avoid the heat, these are also times when pollutants tend to settle closer to the ground. Consider adjusting your routine to mid-morning or early afternoon when pollution levels may be lower. Checking local AQI reports before heading out is essential for protecting your health during outdoor workouts.
Managing Air Quality Risks
While masks became synonymous with safety during the pandemic, most of the masks we relied on for virus protection are not effective at filtering out wildfire smoke or PM2.5 particles. Cloth and surgical masks are designed to block larger droplets but are too loose and porous to trap the fine particulate matter that lingers in smoky air. These particles are especially concerning because they can penetrate deep into the lungs and enter the bloodstream, contributing to inflammation and a range of health risks, including respiratory and cardiovascular problems. N95 masks offer more protection, as they filter out up to 95% of airborne particles, but they are impractical for endurance athletes due to their tight fit and restricted airflow, which makes breathing difficult during strenuous exercise. For runners, wearing an N95 while running outdoors would feel stifling and could impair performance due to oxygen restriction.
So, what should runners and outdoor athletes do when air quality is compromised? The key is to reduce your overall exposure to pollutants. Research suggests that shorter, high-intensity workouts are less harmful than prolonged, steady-state efforts because they limit the amount of time spent breathing polluted air. Instead of logging long miles in smoky conditions, consider swapping your endurance run for intervals, hill sprints, or a tempo workout. These shorter, more intense sessions can provide an excellent cardiovascular boost while minimizing your time outdoors.
Additionally, if your schedule allows, plan your runs for early morning hours when air quality is often better. You can also check local AQI reports before heading outside. If conditions are particularly bad, head indoors to a treadmill or cross-train with indoor activities like cycling or rowing. Keeping a few masks in your workout bag can also be useful if conditions change while you're out. Your lungs—and your long-term performance—will thank you.
The Problem with Particulate Matter
One of the most dangerous components of polluted air is PM2.5, a term that refers to fine particulate matter with a diameter of 2.5 microns or smaller. To put that into perspective, a human hair is about 50 to 70 microns in diameter, meaning these particles are microscopic. Because of their small size, PM2.5 particles can bypass the body’s natural defenses, like the mucus and hairs in your nose, and travel deep into the lungs. Once inhaled, PM2.5 particles can enter the bloodstream, triggering inflammation and oxidative stress that increase the risk of conditions like asthma, heart disease, diabetes, and even lung cancer. For people who are exposed to these particles regularly, including athletes training outdoors, the long-term health consequences can be significant.
Wildfire smoke is a primary source of PM2.5 pollution. For endurance athletes, the danger is amplified. Exercise increases air intake by up to 20 times compared to rest, and mouth breathing during exertion bypasses the nasal filtration system, allowing more pollutants to enter the lungs. Let that sink in: exercise increases exposure to these contaminants by 20 times. This means more PM2.5 particles settle in the respiratory tract, increasing the likelihood of health complications. The result? A decrease in oxygen availability for working muscles, causing fatigue, reduced performance, and impaired recovery. The effects of PM2.5 pollution don’t stop at physical health. Emerging research suggests that long-term exposure can also impact cognitive function, memory, and mood. For athletes who rely on sharp focus during competition, this could be another risk factor to consider. Minimizing exposure to PM2.5 is critical for both short-term performance and long-term health.
How Does Air Pollution Affect Runners?
The relationship between air pollution and athletic performance is complex, but studies show a clear link between airborne pollutants and endurance performance declines. A recent study from Brown University and published in Sports Medicine found that higher levels of PM2.5 had a direct impact on marathon times. For every 1 microgram per cubic meter increase in PM2.5, male marathoners ran 32 seconds slower, while female marathoners ran 25 seconds slower. These delays might sound minor, but over the course of a full marathon, they add up. For example, participants running in high-pollution years may finish nearly ten minutes slower than those running in low-pollution. This can be a significant difference for competitive runners chasing personal bests or qualifying times.
What makes this finding even more concerning is that performance declines were noticeable even when pollution levels were below the EPA’s safety threshold. This suggests that the current standards for what constitutes “safe” air may not fully account for the risks posed to athletes who breathe more deeply and frequently during exercise. When runners breathe heavily during prolonged exercise, they inhale more pollutants than they would at rest. These fine particles settle deep in the lungs and can cause inflammation, reduce oxygen transport to muscles, and impair cardiovascular function. The effects of air pollution may be subtle during training but become more apparent in competition, when athletes push themselves to their limits. In addition to slowing runners down, polluted air can contribute to respiratory irritation, coughing, and difficulty breathing—all of which can make it harder to maintain pace and intensity. It’s important for runners to monitor air quality before heading outside and to adjust their training plans accordingly to avoid long-term damage to their lungs and overall health.
Why Are Some Runners More Affected Than Others?
Interestingly, not all runners experience the same performance decline in polluted air. The Brown study found that mid-pack endurance athletes—those finishing marathons in four to five hours—showed the greatest slowdown. The fastest finishers were less affected, likely because they spent less time on the course and, therefore, had shorter exposure to polluted air. Slower participants, on the other hand, may breathe more lightly, reducing the amount of particulate matter they take in. But mid-pack runners, pushing themselves close to their limits for longer periods, appear to be the most vulnerable to the negative effects of air pollution.
There are several possible explanations for this U-shaped curve in performance impact. One theory is that elite athletes may have adapted to training in polluted environments, building a tolerance over time. They may also spend more time training indoors or at higher altitudes with cleaner air. Recreational runners, however, may not have the same fitness level or physiological adaptations to offset the effects of air pollution, making them more susceptible to the harmful impact of airborne pollutants. Another explanation could be the duration of exposure. While elite runners complete marathons faster, mid-pack runners are on the course for longer, increasing their time spent breathing polluted air. This prolonged exposure, combined with intense physical effort, may amplify the effects of pollutants on the body.
Ultimately, these findings suggest that the impact of air quality depends on both exposure time and intensity of effort. Understanding how pollution affects different types of runners can help individuals tailor their training and race strategies to minimize risk.
Making Sense of Air Pollution's Impact on Your Runs
The idea that air pollution affects athletic performance isn’t new. Recall the 2008 Beijing Olympics, when U.S. athletes wore masks to protect their lungs from the city’s infamous smog. But what’s different about the Brown study is that it shows performance declines at much lower pollution levels than previously thought. The current EPA safety standard for 24-hour PM2.5 exposure is 35 micrograms per cubic meter, and the annual limit was recently lowered to 9 micrograms per cubic meter. However, the study found that even when pollution levels were well below these thresholds, runners still experienced significant slowdowns. This raises questions about whether current air quality standards are adequate for protecting athletes.
For runners, this means air quality is an important factor to consider when planning races or training sessions. Choosing to run on a day with poor air quality could cost you several minutes—an eternity if you’re chasing a personal best or a qualifying time.
There are practical steps runners can take to mitigate the impact of air pollution. Monitoring AQI levels, adjusting workout intensity, and planning routes in less polluted areas are all effective strategies. Additionally, indoor training options, such as treadmills or stationary bikes, can help athletes maintain fitness when outdoor conditions are poor. Ultimately, being aware of air quality and taking proactive measures to reduce exposure can help runners protect their health and performance in both the short and long term.
Breathing Through the Chaos
Being evacuated from my home has made me reflect on the hidden forces that shape our lives—from the fires burning through communities to the air we breathe. Even as the flames move on, the impact lingers. It’s in our routines, in our lungs, and in how we move through the world. We adjust, often without realizing it, to what we can’t control. And just like the smoke in the air, that disruption feels both immediate and long-lasting—reshaping how we think about safety and what it means to simply step outside.
In moments like these, knowing when to be outside, for how long, and how the air we breathe affects our bodies is essential. It’s about awareness—understanding that our surroundings shape more than just our performance. Whether we’re exercising or simply going about daily life, the air we breathe impacts our health, our choices, and our well-being.
What we’re all realizing now is that resilience isn’t about pushing through at all costs. It’s about adapting to what’s around us, adjusting our pace, and protecting ourselves when we need to. Because endurance is about finding a way to keep going—even when the world feels upside down.