Running, bicycling, tennis. Under normal circumstances, exercising outdoors is healthy. And then there are times like right now when parts of L.A. County are so addled with wildfire smoke that the air is considered unhealthy or even hazardous to breathe. According to the U.S. Environmental Protection Agency Air Quality Index, much of Northeastern L.A. County currently falls in that category, due to the Bobcat Fire raging through Angeles National Forest.

Yet many Angelenos are continuing to exercise outside, despite the risks. We reached out to University of Southern California Environmental Health and Preventative Medicine Professor, Ed Avol, to find out more about the health effects of exercising in smoky air.

What You Need To Know

  • Exercising in smoky air has short- and long-term health effects

  • Coughing, shortness of breath, and eye irritation are common short-term effects, but longer-term smoke exposure has the potential to affect most other organ systems in the body

  • To protect against wildfire smoke, masks that fit around the face securely are most beneficial

  • The U.S. Environmental Protection Agency's Air Quality Index can help exercisers understand whether the air is healthy enough for strenuous exercise

What happens when a person exercises in air that is so smoky you can see and smell it?

In the short term, it could be immediate irritation: coughing, eye irritation, difficulty breathing. For those that have pre-existing disease, like asthma, you could potentially trigger an event where you’d have to take medication or have more severe difficulty breathing. The bigger issue is the potential impact on your health over the course of repeated exposures. There are a number of negative health problems associated with long-term exposure to particles and gases that begin with the lungs and respiratory system and extend to most other organ systems in the body.

How much exposure does it take to produce those sorts of long-term effects?

There isn’t any line in the sand because we each vary in terms of our own susceptibility, health status, and receptivity to exposures. Pre-existing conditions and inheritable traits play a factor. It’s hard to say absolutely that this will happen because of that. Short-term effects happen in hours or days or maybe weeks. For long-term effects, we’re talking more about months to years.

How does fire smoke damage the respiratory system?

It has to do with what’s in the air. Smoke is composed of particles and gases, and the particles come in all sizes. In the case of wildfires, we have wood smoke, but the problems also include the conflagration of buildings and power lines and solvents and cars and everything else that goes up into the air. Think about what’s in your garage in terms of cleaners and solvents and paints. All that is burnt, so there's a tremendous amount of chemicals in the air in addition to just the wood smoke. And all those things can potentially challenge your health because you breathe those in. 

How does that affect the human body?

Your body has an amazing array of defense mechanisms, but they’re not 100 percent effective, and they don’t always work. It depends on your individual variability, your general health. You can breathe in certain size particles, and your body will get rid of most of them, but not all of them.

Some will get past all the defensive mechanisms and get down to the air-blood exchange located in the extreme smallest parts of your lungs where the blood-air barrier exists. Once those materials cross over into the bloodstream, they can then potentially go anywhere in your body that the blood system circulates, which is virtually everywhere in your body. 

Similarly, with gases in the air, some of the chemicals in those gases will get through as well. So over the course of time, your body may not be able to systematically, continuously fight off the challenges. Initially, inflammation is a pretty common response. Your body has a natural defense mechanism that things swell up and try to flood the area to protect portions of your body.

There are many things your body can do to try to sequester or close off the particle from coming into contact with other parts of your biological system. There are ways it can detoxify some of the chemicals that come into the system, but none of them are 100 percent, never-fail operations.

As a health professional, and someone who also exercises regularly, how are you changing your behavior to deal with these smoky air conditions?

I’m a regular runner. I’ve missed a couple of days here, which is frustrating because under these stay-at-home orders, you don’t get outside much anyway, so I’m trying to take care of myself by not exercising. We have to be mindful of trying to decrease the exercise levels that affect our ventilation rates -- how much air we breathe and process. I keep windows and doors closed to the extent feasible. I also try to take care of myself by getting adequate rest, sleep, water, liquids, foods, and as challenging as it is, I try to keep a positive attitude.

People exercise for their mental health as well as their physical wellbeing, especially now, with so many people cooped up because of COVID. Should the mental health benefits of exercise factor in at all?

I agree that too often we overlook the importance of the mental health aspect in all of this, and that has been a significant issue with stay-at-home directives. It’s difficult to be away from friends and not have social contact. I see it among many of the students I work with because now all of our classes are on Zoom. It is challenging for us to maintain a positive mental health outlook, and that is an often overlooked aspect of our entire health. To do that we need to acknowledge these are stressful times, reach out to friends, let people know you're thinking of them and that you’re not alone. There’s a sense of loneliness and isolation here that is difficult, so to get past that is a challenge for us all.

What gauge should people use to learn if the air is too unhealthy for exercise?

A number of gauges are available to the public because of the internet. The Air Quality Index is a color-coded indicator that takes into account multiple pollutants and gives you a composite number on air quality in your area. You can find that easily by going to The AQMD has a color-coded ranking for regional air quality. Here in Southern California, we’re challenged even without the smoke. We have occasionally poor air quality days that are in violation of federal and state air quality standards for ozone and particulates (PM 2.5), so even without the smoke, we occasionally have days that are unhealthy to be out and exercise. With the smoke, we have this compounding condition. Search for AQI and see what the estimate is.

Is it possible to tell if it’s too unhealthy just by smell or sight?

That's also an indicator. If you can smell it or see it, chances are reasonable that you’re in fact in the middle of it, and use that as an indicator that maybe I shouldn't exercise in quite the manner I would otherwise. But many pollutants we’re concerned about, like ozone, are clear and colorless, and levels can be high even though you can’t see it. So don’t just rely on your sense of smell and sight.

Is it still OK to walk outside?

Yes, it depends on how vigorous you walk and for how long, but it’s important to appreciate that exercise is good for us. We all need more exercise. We don’t get enough. There’s an epidemic of obesity, diabetes, cardiovascular disease, so going out for a walk is a good idea. Doing so requires some thoughtfulness, such as wearing a mask, staying socially distanced, choosing when and where you walk so it is not during busy times or on busy streets because that exposes you to higher levels of pollution even without the smoke.

A lot of people are already wearing face coverings because of COVID. Do they provide enough protection from fire smoke, or is an N95 mask preferable?

Using a cloth mask helps a little bit but is not as effective to screen out particles as an N95. Masks are typically used to protect yourself from things you’re breathing in from the air. N95 masks are excellent because they essentially take out all the smaller particles. That’s exactly what they’re made for. The problem right now, of course, is many of them are needed for first responders for the COVID pandemic, so there’s not as much access to them. 

Generally all face coverings will do a little bit of good, but a bandanna over your face doesn't help much. If you have a mask, you should use it, but a mask only works if it seals around your face so you breathe through it instead of letting the air get in around the edges. That's usually accommodated by that metal strip or piece of wire in the top to help follow the contours of your face and nose. If the mask doesn’t fit over your face well, it doesn’t matter what kind of mask it is because the air will go around the edges and go in through the leaks.

What advice do you have for people who want to exercise even though the air is smoky?

Unfortunately, the best thing we can do under these smoky conditions is to stay indoors, keep the doors closed, set your air conditioning on recirculation. Try to take it a little easier. Generally, slow it down for a while and give the first responders a chance to deal with this.

This interview has been edited for brevity.