Wildfires are increasingly causing destruction and illness around the world, but the smoke drifting southward from eastern Canada this week is a new experience for the tens of millions who live in the U.S. Northeast.

Many in those states are wondering what they need to know about a first-time wildfire smoke event.

Are health risks lower during a first-time wildfire smoke event?

People in the Northeast may like to think they are not at risk from the wildfire smoke drifting down from Canada because research on health effects comes largely from regions where people are exposed to wildfire smoke for weeks at a time, year after year.

“The bad news is, there’s no safe level” of inhaled particles from wildfire smoke, said Doug Brugge, a public health researcher at the University of Connecticut School of Medicine. “The higher the exposure, the worse the risks, but even at levels below the national safety standards, these particles can make people sick.”

Any amount of inhaled particles will trigger inflammatory responses in the body. Children, the elderly and people with chronic cardiac, respiratory and other illnesses are most vulnerable. People with long COVID may also be more vulnerable, because many of them have persistent lung damage.

But even in healthy adults, some effects of exposure — such as sore throats, excessive phlegm, coughing, headaches and brain fog – can appear immediately and often persist long after the smoke plume is gone, said Keith Bein of the Air Quality Research Center at the University of California, Davis.

Are people safe indoors?

Particulates from wildfire smoke enter most buildings in high concentrations, experts say.

The problem is greater in older structures, which tend to have windows and vents that are less well sealed than in newer buildings.

On average, when you are indoors, the concentration of wildfire pollutants is about half of what it is outdoors, according to Dr. Jasvinder Singh, a lung medicine specialist at Medstar Franklin Square Medical Center in Baltimore.

If a building is not well sealed, the concentration may be up to 70 percent of what it is outside, he said.

The U.S. Environmental Protection Agency advises that during wildfire smoke events, people avoid indoor activities that put more fine particles into the air, such as smoking cigarettes, frying or broiling food, burning candles or incense, and vacuuming without a HEPA filter.

Bein of UC Davis compared indoor wildfire smoke exposure to second-hand tobacco smoke exposure.

“The particles penetrate your home,” he said. “They end up everywhere – on your clothes, on your walls, on surfaces and they’re still outgassing” – being released into the air – “after the smoke plume is gone.”

Experts recommend indoor use of air purifiers that can trap particles smaller than 2.5 microns, especially for those at risk. For those who cannot afford to buy one, researchers at UC Davis offer simple instructions for building one.

Should healthy people stay inside?

Even healthy people should avoid being outside when the air quality is dangerously low and in particular they should avoid outdoor exertion. The longer you are outside and the harder you breathe, the more pollution you inhale, Singh said.

Are there any special considerations in the U.S. Northeast?

Compared to Western regions of the United States, Northeastern and Middle Atlantic states may have more old buildings, which means people may be exposed to greater amounts of pollution through drafty windows and doors.

The Northeast also has more urban areas with higher population density, which has been linked with higher rates of heart disease, asthma and other respiratory diseases.

– Reuters. Edited for style.