Jenny Edwards didn’t want to go back home to Canberra, the Australian capital. She added seven days to a five-day family vacation “specifically to stay out of the smoke.” But it didn’t matter.

Within a day of returning, her eyes were irritated, her chest felt tight, her head hurt and a small but persistent cough couldn’t clear a tickle in her throat. Three massive fires were still burning about 60 miles away, and even though the heaviest smoke had momentarily lifted, the misery of living in a brownish haze remained. Air quality in Canberra on New Year’s Day was among the worst of any major city in the world.

Australia’s bush fires have blanketed parts of the continent with pollution, affecting hundreds of thousands of people who are not in immediate danger from the flames. Government agencies and medical officials say distress calls, ambulance runs and hospital emergency room visits have surged. Even some federal departments in the capital had to temporarily shutter offices and tell nonessential staff to stay away.

Stores have seen an overwhelming demand for smoke filtration masks, and in recent days government officials have begun rationing them to particularly vulnerable people, including pregnant women, the elderly and those with chronic heart and lung conditions. On Facebook, residents have posted pictures of doors and windows sealed with thick tape in an effort to keep smoke out their houses. And 7News Sydney posted a “Ciggie Index” — the equivalent number of cigarettes each resident consumes daily from inhaling smoke. In east Sydney, it’s 19.

A key question lingers as the fires that began last year continue to burn, in some cases merging into megafires: What are the long-term health implications of so many people exposed to thick smoke for so long?

Wildfire smoke that lingers for weeks doesn’t just get into people’s eyes and the pores of their skin, researchers say. It enters their minds, settles in their thoughts and affects their mental health. That was a finding from studies following the deadly Black Saturday fires in Victoria in 2009, when both firefighters and residents suffered from post-traumatic stress.

“I’m predicting that the effect is going to be far greater than before because the fires have been burning for such a long time,” said Mirella Di Benedetto, a researcher and clinical psychologist at RMIT University in Melbourne. The 2009 fires were isolated to Victoria, but the current fires are burning nationwide, near Australia’s largest cities. “Even where there are no fires, smoke is moving down to these areas,” Di Benedetto said. “The air quality is really bad in Sydney. I think the mental health and physical health impact will be huge in the months to come.”

Little research exists about the long-term consequences of exposure to wildfire smoke, but Kari Nadeau and Mary Prunicki, scientists at Stanford University, are working to change that.

They’re closely following hundreds of people affected by devastating wildfires in California, taking blood samples and asking them about everything from their use of air filters to their psychological responses to the experience. Earlier research has linked air pollution from wildfires to a range of acute conditions, including asthma, heart ailments and strokes, but Nadeau and Prunicki hope to solve a deeper mystery.

“Are there irreversible consequences over time?” said Nadeau, director of Stanford’s Sean N. Parker Center for Allergy and Asthma Research.

The work is urgent, Prunicki said, not only because existing research is limited, but also because the rapidly warming climate is likely to make the unprecedented fires in Australia only more common there and elsewhere around the globe.

“They are not going to go away,” she said.

In Australia, the smoke is affecting cities in unexpected ways. At one of Canberra’s public hospitals, workers kept the hospital’s exterior doors shut to keep smoke from clouding the hallways and patient rooms, said David Caldicott, an emergency room physician.

Some nurses wore breathing masks, and the smoke temporarily incapacitated some local MRI machines, he said. At his own house, the smoke detector kept blaring one day until Caldicott finally muffled it with a towel at 3 a.m.

In an arid country where residents are accustomed to a wildfire season, he said, the past weeks have been unlike any he has experienced. “It’s sort of like medicine meets ‘Mad Max,’” Caldicott said, referring to the vintage Australian action movie about a dystopian, post-apocalyptic future.

In the state of New South Wales, home to Sydney, health officials said emergency room visits for asthma and breathing problems increased more than 34 percent in the period from Dec. 30 and Jan. 5 compared to a year earlier. Ambulance calls for respiratory issues were also higher, about 2,500 compared to the five-year average of about 1,900. Similarly, hospital admissions increased to more than 430, surpassing the five-year average of 361.

Four of Australia’s five largest population centers are experiencing the effects of the fires. At least 25 people have died, nearly 2,000 homes have been destroyed and more than 14 million acres have burned. So much smoke has been produced, there’s evidence that some is circumnavigating the planet and has reached South America, according to the National Oceanic and Atmospheric Administration.

Bush fires are a known trigger for asthma attacks, said Bruce Thompson, dean of the School of Health Sciences at Swinburne University of Technology in Melbourne. “This is a very significant health concern. Here in Australia, we’re making sure people are moving themselves from the outdoors as best they can,” Thompson said.

Inside bush-fire smoke, water vapor intermingles with tiny particles measured in micrometers. It also contains gases such as carbon dioxide, nitrogen oxides and carbon monoxide. Wood dust from exploded trees and chemicals from melted tires and scorched steel also hitch a ride.

Particles as large as 5 micrometers “stick in your nose; you wake up with a runny nose and itchy eyes,” Thompson said. Particles as small as 2.5 micrometers — known by researchers as PM 2.5 — are scarier, he said. “They can get to the very edges of the lungs,” Thompson said. “We had a coal mine fire a few years ago and it’s been demonstrated that four years after, children close to the plume had worse lung function. So this is bad.”

Smaller particles in smoke can hinder cardiac function in adults. Thompson said the developing lungs of children can be permanently damaged in varying degrees.

“The lung becomes inflamed, and you cough as the lung tries to adjust,” Thompson said. “The lung is bad at repairing itself. It tries to get rid of particles by making you cough, but it produces scar tissue, and you don’t want that in the lung because it changes the efficiency of the lung.”

Fay Johnston, an environmental health professor at the University of Tasmania’s Menzies Institute for Medical Research, said most people exposed to the smoke won’t be harmed — as long as the fires end soon.

“If the smoke goes away, a healthy person can withstand it,” said Johnston, who specializes in the health effects of bush-fire smoke. “Healthy people will come through it without any long-term harm.”

But relief from the yearly rainy season isn’t expected until February. Like other researchers, Johnston worries about what will happen if the fires continue, particularly for old and young asthma sufferers. “What’s the long-term legacy of it?” she said. “We really don’t know.”

Few studies have delved into the consequences of long-term exposure to bush fires. Johnston and other researchers conducted the study Thompson referenced, on health impacts on children and mothers in the wake of a 2014 fire at a Victoria coal mine that burned for more than a month, blanketing the nearby town of Morwell with smoke.

Young children exposed to the smoke were more likely to get an antibiotic prescription in the year after the fire, and pregnant women were more likely to develop gestational diabetes, Johnston said.

Bin Jalaludin, a professor at the University of New South Wales and chief investigator at the Centre for Air Pollution, Energy and Health Research, said government officials and academics in Australia already have been brainstorming ways to study the long-term health implications of the “truly unprecedented” fires.

“What we want to look at is things like ER visits, deaths, hospitalizations, ambulance call-outs for respiratory problems, birth outcomes — do women who are pregnant and exposed to high levels of smoke, does it have an impact on the newborn?” he said. “It will take time, although we are trying to expedite it and get some of this work done quickly.”

Meanwhile, south of Sydney in Bowral, Peggy Stone said she’s fighting off feelings of depression. “We haven’t seen the sun for weeks,” she said. The sky is sometimes fiery orange, sometimes smoky gray. The day she spoke, she said, “The sun is trying to penetrate the smoke. Occasionally it might try to get through and we get a little ray.”

Farther south in Canberra, Jenny Edwards, who has asthma, made an appointment to see a doctor.

“I’m quite worried about the next couple of months,” Edwards said. “Air quality is so hard to predict with so many large fires in our region and the possibility of new ones starting.”

She’s thinking of leaving Canberra — again. But she knows that option is also risky because it’s hard to escape the reach of the fires.

“I am considering returning to stay with my mother-in-law near Lake Macquarie,” she said. “Mind you, there are big fires inland from there, and while staying there last week we had three small fires break out within 10 kilometers of us.”