Breathing Poison: You Can’t Outrun Wildfire Smoke

On Sept. 6, 2020, San Francisco hit 100 degrees — a rare event in the city’s recorded history.

Eight months pregnant, Alana Semuels baked in her west-facing apartment. The air outside smelled like a campfire. The haze swallowed the sun and blurred the outlines of Alcatraz Island and the Golden Gate Bridge.

“It was like an oven,” she recalled. “One night, I got so desperate that I went outside to sleep on our deck chairs. It felt like the only place I could go to really breathe. I remember waking up with a fine layer of grit on the chairs and on me.”

A few weeks earlier, a barrage of dry lightning sparked hundreds of wildfires across the Bay Area. For 30 straight days, officials urged locals to stay inside because the air was so unhealthy. Tiny specks of soot and ash exceeded the safety guidelines set by the federal Environmental Protection Agency. It was even worse in the Sierra Nevada, the Sacramento Valley, and parts of Southern California.

The month-long haze has become a grim preview of California’s new reality. Wildfire smoke is now three to six times worse than it was a decade ago. Scientists have linked exposure to higher risks of heart disease, cognitive decline, and pregnancy complications. The evidence for these health effects is now stronger and more wide-ranging than many experts anticipated back in 2020.

Before long, Semuels began coughing. Concerned for her baby’s developing lungs, she called her doctor.

“You just worry, is this gonna hurt my baby somehow?” she said. “That’s just really unnerving because there’s really nothing you could do about it.”

A nurse told Semuels to find an air-conditioned space. But it was the pandemic, so restaurants and theaters were closed. She tightened her mask and wandered through a Target, buying nothing.

“It was like, this is the new paradise,” she said. “The inside of a box store.”

It was a smart move. Pregnant people are more likely to suffer from heat exhaustion or heat stroke because their bodies have to work harder to cool themselves. And, there’s growing evidence that wildfire smoke can increase the risk of preterm births, lower birth weights, and even hinder healthy development.

“The placenta doesn’t fully protect the fetus from these kinds of stressors,” said Carlos Gould, environmental health scientist at UC San Diego. “There’s quite strong evidence that a bad wildfire smoke day can increase these risks by five to 10%.”

Children are also vulnerable to smoke exposure because they breathe faster than adults and their lungs are still developing. It can worsen asthma, trigger respiratory infections and limit lung growth.

The most at risk, Gould said, are older adults. In 2020 alone, he estimated, wildfire smoke killed tens of thousands of people across the country,  most of them seniors. And because smoke can travel thousands of miles, the danger isn’t limited to those near the flames.

“Where the wind blows, so too goes smoke,” he said.

Scientists are learning that wildfire plumes can trigger surprising medical issues like rashes, stomach aches, and raise a person’s risk of developing dementia. Even suicide rates rise when it’s smoky. Emerging research suggests that tiny particles in wildfire pollutants may weaken the immune system, even just weeks after a fire.

“This chronic short burst exposure can have some lasting effects on the immune cells,” said Sharon Chinthrajah, an asthma specialist at Stanford. “These are your first lines of defense.”

Today wildfire smoke accounts for roughly half of the state’s air pollution, yet it’s classified as an “exceptional event” under the Clean Air Act — meaning much of the toxic air people breathe goes unrecorded by local air districts.

To protect yourself, Dr. Chinthrajah advised checking local air quality regularly and avoiding outdoor activity on hazy days. She also recommended investing in air filters.

For  Semuels the stress of the 2020 smoke event — pregnant, overheated, and surrounded by toxic air — was too much – even though she says, ‘San Francisco is her favorite place on the planet.’

“It’s just a place that kind of makes my chest relax and I just love it,” she said. But I just felt like we couldn’t do that summer after summer after summer.”

Her family moved to New York’s Hudson Valley after her child was born, a healthy baby boy. But a few years later, smoke from Canadian wildfires drifted into the region, turning skies an eerie orange and sending air quality readings into the hazardous territory. And the wildfire smoke was back again this summer, too.