How Bad Is Wildfire Smoke for Your Health?

[Originally published: Jun 26, 2023; Updated: Jun 28, 2023.]

It hasn’t been that long since the threat of COVID-19 drove people outdoors to avoid infection. Now, people living in the Northeast and Midwest are encouraged to do the opposite as wildfire smoke from Canada creates poor air quality hundreds of miles from the flames.

Stay inside. Wear masks. Get an air purifier. The advice from public health and medical experts has been consistent. And, as with the COVID-19 variants that caused surges followed by periods of relative calm, air quality has gone back and forth between healthy and unhealthy levels.

As long as there are wildfires, experts expect these shifts in air quality to continue. Below, Yale Medicine’s Carrie Redlich, MD, MPH, who is trained in internal medicine, pulmonology, and occupational and environmental medicine, discusses air quality and how we can stay safe.

The United States Environmental Protection Agency (EPA) established an Air Quality Index (AQI) to measure air pollutants. A higher AQI, with color codes and corresponding numbers (ranging from 0 to 500), means a greater health concern. (Local AQI information is available on various apps and websites, including www.airnow.gov.)

Particle pollution, also known as particulate matter (or PM), is a type of air pollutant made up of tiny particles of solids or liquids suspended in the air. It’s one of the main components of wildfire smoke, which is a mix of gases and fine particles from burning vegetation, as well as building and other materials.

Particulate matter includes PM10, inhalable particles that are 10 micrometers and smaller in diameter, and PM2.5, inhalable particles with diameters of 2.5 micrometers and smaller. PM2.5 poses a greater health risk than PM10 because the particles are so small (30 times smaller than the diameter of a human hair) and can get deep into the lungs and bloodstream.

Although air pollution is not good for anyone, certain groups are more sensitive to it than others, including those with heart or lung disease, older adults, infants and children, and pregnant women. As the AQI levels increase, the risk of health effects increases, especially among these more sensitive groups.

“The advice to limit strenuous activities is because when your respiratory rate is higher, you inhale more particulates,” says Dr. Redlich.

When the AQI is 201 and higher, everyone should be concerned about health risks and limit physical activity outdoors as much as possible, she adds.

For context, with the recent wildfires in Canada, the PM2.5 AQI climbed above 400 for a brief period in New York City in early June.

PM2.5 particles are so tiny that they get through the usual defense mechanisms of the upper airway and can penetrate deep into the lungs, where they can impair lung function, cause illnesses, such as bronchitis, and increase asthma attacks. The particles can also pass into the bloodstream and travel to other organs, where they can cause damage. In addition to respiratory problems, PM2.5 exposure has been linked to an increased risk of heart attack, stroke, lung cancer, and a decline in cognitive function.

“The health effects extend beyond respiratory issues and include the cardiovascular system,” Dr. Redlich says. “There is more extensive literature on particulate air pollution, in general, than forest fires specifically, but the indication is that wildfires have similar health effects. And there has been an explosion in research and understanding that even relatively low levels of air pollution can impact your lungs and heart, especially if you have asthma, chronic obstructive pulmonary disease [COPD], or cardiac disease.”

The reason particle pollution has such systemic effects, Dr. Redlich explains, is that when you inhale these tiny particles, “they get everywhere through the bloodstream and trigger inflammatory pathways, which can exacerbate a number of underlying cardiac and respiratory conditions.”

Furthermore, even if you don’t see or smell smoke in the air, it can still affect you, she adds.

The EPA has an AQI for five major pollutants: ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. However, the two air pollutants of greatest health concern in the U.S. are particles and ozone.

Ground-level ozone is created by pollutants from cars, power plants, refineries, and other sources reacting chemically in the presence of sunlight.

“Ozone levels are generally highest on hot, sunny days, often in the summer in the late afternoon and evenings,” Dr. Redlich says. “High ozone levels can also aggravate lung diseases, such as asthma, bronchitis, and COPD.”

For many people, the symptoms of inhaling particulate matter are similar to what someone with allergies experiences: stinging eyes, scratchy throat, runny nose, coughing, sinus irritation, wheezing, and shortness of breath. Breathing in smoke can also cause headaches, fatigue, and a fast heartbeat.

If the above symptoms are minor, there’s no reason to seek medical care, Dr. Redlich explains. However, if you have asthma and the outdoor air quality causes an exacerbation that you can’t manage at home, such as with a rescue inhaler, you should contact your doctor, she adds.

“Or, if you are having chest pain or trouble breathing, you should contact your medical provider,” Dr. Redlich says.

Children are more likely to be affected by air pollutants because their airways are small and still developing, and they breathe in more air relative to their body weight than adults do, according to the Centers for Disease Control and Prevention (CDC). Plus, kids typically spend more time outside than adults, which places them at higher risk.

Through its color and number system, the AQI spells out recommendations on when everyone should avoid being outdoors. But what if the AQI is “unhealthy” and you aren’t considered high risk? Is it OK to go for a run outside—or even a brisk walk?

Dr. Redlich doesn’t have a firm answer to that question. “I would be more concerned if someone has a pre-existing heart issue, and this might be the thing that tipped the balance,” she says. “It’s harder to say what the risk to any one person is of, say, three days of poor air quality. Still, even at low levels of air pollution, studies have shown adverse health effects across a large population.”

However, if someone comes to the hospital with a cardiac event, it typically is not associated with high air pollution levels, she adds.

The best type of mask to wear for protection against wildfire smoke is a well-fitted N95 or P100 respirator with two straps that go around your head. The “95” and “100” refer to the percentage of particles filtered out by the mask. They are not specially made for children.

“A surgical mask probably does some good, but the N95 or even a KN95 is better,” Dr. Redlich says. “KN95s may be easier to find and may come in sizes that fit children better.”

The EPA provides a one-sheet with information on how to choose the right mask for wildfire smoke.

When the air quality is poor, the general advice is to go inside, shut the windows, and use an air conditioner (with a clean filter and the fresh-air intake closed). But, not every home has air conditioning or can be tightly sealed to keep the bad air out, Dr. Redlich explains.

“It’s not as though you go inside and the level drops to zero. Yes, going inside is usually a good idea, but you can also store poor air quality levels—or even air pollutants—in your home,” she says. “Plus, you can generate air pollutants inside by cooking, smoking cigarettes, and burning candles.”

These, Dr. Redlich says, are all things we have control over and can be avoided or mitigated with steps like using a vent over your kitchen stove.

Another step people can take to improve particulate air quality or reduce particulate air pollution in their homes is to use a portable air purifier with a HEPA (high efficiency particulate air) filter. The air purifier should be sized appropriately for the size of the room.

And if none of these protective measures can work for you, seek emergency shelter if the smoke is affecting your health.