Chelsea Holtsoi lives on the Navajo Reservation, in a home with five of her kids, near the town of Many Farms. They don’t have indoor plumbing or central heating. There’s an outhouse 50 yards away, on the field of hard-packed dirt where their cabin sits.

Her son Ethan, 10, likes playing football with his friends, and his favorite subject at school is math.

When he was 3, Ethan got a terrible fever.

“He’s burning up,” Holtsoi remembered. “I started getting scared, and ice water we got. We put a rag in it. We rung it out. We’re just wiping his body down. Pretty soon, the water was warm from just wiping him down.”

When the ice water didn’t help, Holtsoi gave her son ibuprofen, but his temperature just kept going up, she said.

“It’s really a scary experience, especially when they’re that small,” Holtsoi said. “It just hurt, just looking at him.”

Holtsoi rushed him to the nearest clinic. There, the doctors told her Ethan didn’t just have a fever — he was having an asthma attack, and his oxygen levels were alarmingly low. They told Holtsoi they wanted to send him to an intensive care unit in Phoenix, which would be a five-hour drive.

Instead, Holtsoi and Ethan boarded a medevac plane, and off they went.

Asthma is on the rise across the United States, and the problem is particularly grave on reservations. There, asthma rates are high. Kids are more likely to have asthma attacks, and more likely to die from the condition. And emergency rooms are far away.

The Navajo Reservation is a vast desert landscape the size of West Virginia. It’s dry, dusty, and windy. It’s bitterly cold in the winter. Rock formations and red and brown dirt stretch for miles, dotted with sparse shrubs. It takes hours to drive between towns, and there can be miles between houses. Many roads are unpaved, and hardly anyone has an address.

Holtsoi remembers the night she and Ethan took that medevac plane to Phoenix, “I just kept looking at him and I was scared,” Holtsoi said. “And I just kept praying and praying and praying when we were in the plane. No parent should ever experience that.”

Ethan had to spend about a week in the ICU before he was well enough to leave.

Since the 1980s, asthma has been increasing across all ages and ethnic groups in the U.S., but it’s a bigger problem among Native Americans. People living on the Navajo Reservation, for example, are 1 ½ times as likely to have asthma as people living elsewhere in the country.

“The environmental exposures here are impossible to control,” said Diana Hu, a pediatrician who’s been working on the Navajo Reservation for 35 years.

Some of the causes of asthma on the reservation are old, she said: “We have, you know, Russian thistles or tumbleweeds everywhere. We have elms everywhere. We have cottonwoods everywhere.”

Those are all plants that can set off kids’ allergies, which can trigger asthma attacks. There’s some evidence that climate change is increasing the amount of pollen in the air, which some researchers say is contributing to the rise of asthma.

Other factors that contribute to asthma are new. There are fossil fuel projects, like coal mines, on the Navajo Reservation. Air pollution from coal mines is associated with increased asthma.

There are daily one-to-two-hour drives on diesel school buses from far-flung houses to the towns where the schools are located. Diesel fumes can both cause and exacerbate asthma.

And there’s something else.

“We always had a wood stove,” Holtsoi said. “That’s one thing I didn’t really want to use as a heating source, but it’s all we could afford.”

About two-thirds of families on the Navajo Reservation heat their homes with wood stoves.

The Holtsois’ stove is black, with a little door for putting wood in and a wide stovepipe coming out of the back. It has no filter to keep smoke and ash out of the cabin, the way more expensive wood stoves do.

Holtsoi said wood costs her $100 for a truckload. Wood pellets burn cleaner but would cost $20 for a small bag. She can’t even consider electric heat, though she wishes she could. When it’s smoky, it triggers Ethan’s asthma.

“He gets really mucusy,” she said. “It’s like boogers, and it’s like you can hear it. You can hear those boogers, and he’ll try to spit it out and sounds congested.”

To try to keep Ethan healthy, Holtsoi makes sure the stovepipe is always clean, so smoke won’t blow back into the cabin. And she always has a pot of water on the stove, so there’s steam in the air.

“The doctors told us to make sure you always have a pot of water to keep the air kind of humid, not dry,” she explained.

When federal agencies like the Centers for Disease Control and Prevention have tried to help lower asthma rates on the reservation, the efforts have often been met with resistance.

That’s why, on some reservations, researchers and health care providers are trying new, community-based approaches.

“Our main goal is really to educate the Navajo Nation: first the hospital staff, and also the schools,” said Stevick Jim, project manager of a program run by the University of Arizona working on community asthma education.

“We want to educate: This is what asthma is, these are what triggers are, before it gets to that extreme level,” he said.

Educating the community has been challenging, Jim said. For one thing, older generations on the reservation aren’t always familiar with the condition.

There isn’t even a word in Navajo for asthma, so it’s hard to explain to grandparents, who are often the caretakers, that it’s a chronic condition that needs regular medication.

Jim said his goal is prevention: teaching caregivers how to help avoid medical crises. The aim is to make minor changes that can help prevent asthma attacks, like staying inside when the pollen count is high, or rolling up school bus windows so kids aren’t exposed to so much diesel exhaust.

Ethan’s doing better. Holtsoi said the doctors put him on a new medication, and he hasn’t been to the emergency room since.