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Parts of US face poor air quality as wildfire smoke lingers. What are the health effects?

Smoke from Canadian wildfires continues to drift into the United States, causing poor air quality for millions. Experts discuss the health effects and how to stay safe.
/ Source: TODAY

As smoke from ongoing wildfires in Canada continues to sweep across parts of the United States, millions of Americans are facing hazy skies and poor air quality for the second time this month.

Just three weeks ago, the Northeastern U.S. became engulfed by plumes of smoke from uncontrolled blazes raging in Nova Scotia and Quebec. Air quality advisories went into effect for millions and a thick haze blanketed areas like New York City, Boston, and Philadelphia, the TODAY show previously reported.

On June 28, about 87 million people are again at risk for poor air quality due to drifting smoke from the Canadian wildfires and ozone impacts, with alerts in place for parts of the upper Midwest, Great Lakes region, mid-Atlantic and Southeast, NBC News reported.

As of June 28, Chicago, Detroit and Minneapolis were among the top cities with the worst air quality in the world, according to the tracking service Residents in some cities were warned to stay inside as air quality remained at unhealthy levels.

Eery images of hazy skylines — reminiscent of those from a few weeks ago — are circulating again social media, prompting concerns about the health effects.

The hazy skies and poor air quality are expected to linger this week and worsen for the New York City region as smoke continues to drift from the wildfires, prompting health warnings from officials, NBC New York reported.

In other parts of the country, including the Midwest and South, high concentrations of ground-level ozone or smog continue to cause poor air quality. Additionally, millions of Americans are facing severe storms and heat advisories.

What causes poor air quality?

The most common causes of poor air quality are high levels of ground-level ozone and particulate matter, according to the National Weather Service, which result from a mix of natural and human activities that cause air pollution.

Fine particulate matter are tiny airborne particles in smoke, soot, dust, and dirt emitted from things like vehicles, factories, and fires, per the NWS.

Air quality is measured with something called an Air Quality Index or AQI, which ranges from 0 to 500, according to, which collects data and provides the public with air quality conditions.

The higher the AQI, the higher the level of air pollution and public health concern. An AQI value below 50 is considered good, any AQI over 100 is considered unhealthy for sensitive groups, any AQI over 150 is unhealthy for all groups and any AQI over 150 is very unhealthy, per AirNow.

Once the AQI reaches 300, it is considered hazardous which is the most severe level of concern. Earlier this month, the AQI in New York City neared 400 — currently, it remains at an unhealthy or very unhealthy level in many parts of the Midwest.

What are the possible health effects of poor air quality caused by wildfire smoke and how can people stay safe?

What are the health effects of poor air quality from wildfire smoke?

“When we inhale, the particles (from smoke) stimulate our airways to become inflamed to not function normally,” Dr. Ronald Crystal, a pulmonologist and the chair of genetic medicine at Weill Cornell Medicine, tells

Wildfire smoke can affect everyone, but certain groups are at higher risk of breathing difficulties and other health issues.

In healthy individuals, poor air quality isn't much of a concern in the short term, but it can cause irritation. "You may cough a bit or feel a little tickle in your throat ... but it's not a permanent problem," says Crystal, adding that these symptoms should resolve as air quality improves.

Other common short-term effects include: burning in the eyes, eye irritation, cough, wheezing, chest tightness, fatigue and headaches, Dr. Roshini Rajapaksa of NYU Langone told TODAY in a segment aired June 8. (If any of these symptoms feel severe or concerning, seek medical attention.)

"The risk is for individuals who have preexisting lung disease, particularly asthma, chronic obstructive pulmonary disease, and people who have post-COVID respiratory problems," says Crystal.

The particles can actually stimulate the airways to constrict, he adds. "These individuals already have a problem of constricted airways — for example, patients with asthma wheeze — so the inhalation of the particles can exacerbate the problem."

Over time, the fine particulate matter from smoke can cause inflammation and damage the lungs, which can impact lung function or increase the risk of other issues, Dr. Purvi Parikh, an allergist and immunologist with the Allergy & Asthma Network, a leading advocacy group for people with asthma and allergies, tells

In addition to worsening underlying respiratory conditions, inhaling these particles also increases the risk of infection, and it can worsen allergies, Dr. Natalie Azar, NBC News Medical Contributor, said on TODAY in a segment aired June 8.

Children, especially those who are immune-compromised, and the elderly are also at higher risk, as well as people with underlying heart disease. “Anything that stresses the lung can stress the heart," says Azar.

While it's unclear exactly how many more days the latest wave of wildfire smoke will linger and how long air quality will remain unhealthy in parts of the U.S., Crystal explains that the rain and wind can help dissipate the air pollution.

The experts recommend checking the AQI or air quality reports (which are available on most weather apps and websites) if you live in an affected area to get the latest information.

Signs to seek medical attention

Parikh advised seeking medical attention if you experience any of the following:

  • Coughing (more than a light, dry cough)
  • Wheezing or whistling sound when breathing
  • Chest tightness or pain
  • Trouble breathing
  • Headaches
  • Sore throat (more than slight irritation)
  • Dizziness

Itchy eyes, a light, dry cough, or an irritated throat are not usually reason to worry about your health in poor air quality, Azar said.

How to stay safe when air quality is unhealthy

When the air quality is considered unhealthy or you're impacted by events like the current wildfire smoke, there are a few steps you can take to protect yourself and minimize the health effects.

The most important thing you can do is stay indoors as much as possible, the experts note. This advice applies to everyone but especially to individuals with preexisting lung diseases such as asthma, COPD and post-COVID respiratory conditions, says Crystal.

You should also consider driving instead of walking to wherever you need to do, Rajapaksa advised.

"Anybody with pulmonary problems should be very, very careful and stay indoors as much as possible," says Crystal. The same goes for pregnant women, says Parikh, as they are also high risk because they are already in a "stressed" state.

When you're inside, make sure to keep all doors and windows shut to reduce the amount of outside polluted air getting indoors, says Parikh. "If you have a HEPA air purifier, you can run it in your home, as well," she adds.

If you're air purifier is too small to service your entire home or an entire large room, Rajapaksa suggested using it in a smaller room and trying to spend most of your time there.

It's generally safe to use air conditioning when the air quality is bad outside. However, the AC should be set on recirculating air mode, says Azar, so that the unit is not pulling in air from the outside and bringing in fine particulate matter.

"If you have fans, turn them all on, (but) watch out for bathroom fans and also vent hoods if they blow in air from the outside," Azar adds.

Even if you’re very careful, some pollution will likely make its way into your home, so Rajapaksa also suggested limiting vacuuming and cooking, as these activities can worsen air quality indoors. For similar reasons, don't burn essential oils or vape or smoke inside when outdoor air quality is bad, Azar advised.

If you have to go outside when the air quality is bad, wear a mask, the experts emphasize. "Medical grade masks are best, such as N95s, KN95," says Parikh. Make sure the mask is worn correctly and covers the mouth and nose, fitting snugly on the face.

“Make sure you have enough of your preventative and controller medications if you have lung issues,” says Parikh. If you use a rescue inhaler, for example, keep it with you at all times.

According to Azar, asthmatics who use a rescue inhaler such as albuterol can use it 15 minutes before going outside.

All exercise and sports should be indoors when the air quality is considered unhealthy for all groups or worse, says Parikh.

“If you’re running, for example, you’re going to be breathing in more because you’re exercising, so you’re inhaling more air and exposing your lungs to more irritants,” says Crystal, adding that this may make breathing uncomfortable or cause phlegm production.

You can use the AQI or reports to find out when the air quality is no longer considered unhealthy and it’s safe to exercise outside again, but always talk to your health care provider if you have questions.