Smoke from Canadian wildfires traveled across the border to the east coast Tuesday evening, engulfing the sky in an eerie, yellowish haze. Even with the fires hundreds of miles away, east coast residents reported smelling the smoke.

“It’s so intense that it stings your eyes,” one tweet read Tuesday about what it was like in New York City.

The air quality index (AQI) surpassed 200 Tuesday evening, according to IQair, a level deemed “very unhealthy”—putting the major metro at the top of the list for worst air quality in the world. New York City officials ordered a poor air quality alert, and now, up to 100 million people are under similar warnings across the Northeast and beyond. As of Wednesday midday, the AQI in New York City is 166—still nearly 17 times the WHO’s appropriately deemed value.

Wildfires can spread harmful particles into the air, seeping into people’s lungs and harming the respiratory system.

With climate change, the United Nations Environment Programme warns wildfires will become more common and even more aggressive as time goes on, begging the question of how poor air quality will affect people’s health in the future—even when this week’s apocalyptic-esque sky dissipates.

Here is what to know about staying safe during poor air quality alerts

What is the health risk of poor air quality?

Those at high risk for health problems due to poor air quality include the very young, older adults, and those with lung diseases like asthma or chronic obstructive pulmonary disease which trigger breathing problems. Poor air quality can exacerbate these symptoms and inflame the lungs.

The longer you are outside during this time, the more severe the risk, says Dr. Eric Costanzo, the chief of critical care at Jersey Shore University Medical Center.

For those at high risk, limit time outdoors as much as possible and carry your rescue inhaler with you, he says. “If your eyes are inflamed and watering, then you can only imagine what that does to the lungs.”

For those without underlying conditions, it’s trickier to tell the direct impact of poor air quality, Costanzo says. Still, the air quality seen this week in predominantly the Northeast was deemed harmful for everyone.

“Your body gives you warning signs,” he says. “If you have that itchy, watery sensation in your eyes, if you feel a little bit of difficulty taking a deep breath in, I adhere to as little time outside as possible when the air quality is bad.”

Should I wear a mask?

In New York City, officials recommended high-risk individuals mask up when going outdoors so damaging particles can be filtered out.

“If you are an older adult or have heart or breathing problems and need to be outside, wear a high-quality mask (e.g. N95 or KN95),” per a statement from Mayor Eric Adams Tuesday evening.

What can you do indoors?

Indoors, it’s important to keep windows and doors shut and circulate air as much as possible.

“For people with allergic asthma, an air purifier with a HEPA filter helps to filter small particles,” says Dr. Jorge Mercado, associate chief of pulmonary, critical care, and sleep medicine at NYU Langone Hospital in Brooklyn.

Central air conditioning can help circulate particles indoors if on recirculate mode. However, portable air conditioners “typically vented out of a window” can cause smoky particles to enter a home, according to the United State Environmental Protection Agency. Still, you can use them if the setting circulates only indoor air and the outdoor duct is closed.

If you have concerns about your indoor air, using fans indoors also helps to stay cool.

You can learn more about indoor air quality at the EPA’s website.

Can I exercise outdoors during poor air quality alerts?

While movement is important for physical and mental health, poor air quality can affect performance and do more harm than good to the body.

“You have to transition your athletic activities indoors and limit your time outside because it can even affect healthy lungs,” he says. “That effect can be sort of an irritant that causes a lot of inflammation in the lungs.”

Despite June 7 being National Running Day, New York Road Runners, an NYC nonprofit, recommended runners adhere to their city’s guidelines and take the day off the trails.

“If you’re in NYC or any affected area, please read and follow your city’s health advisory regarding air quality, and consider running another day,” their tweet read Tuesday.

June 7 is Global Running Day, but if you’re in NYC or any affected area, please read and follow your city’s health advisory regarding air quality, and consider running another day. pic.twitter.com/YPYfgr284b

— New York Road Runners (@nyrr) June 6, 2023

For short-term symptoms, are there any medications to take?

For those who feel irritation in their airways, an over-the-counter antihistamine can help, Costanzo says.

For more severe symptoms, it’s important to consult with your doctor.

The office of the New York City mayor warns conditions may get worse throughout Wednesday afternoon and evening.