Sydney residents are taking precautions against air pollution Bloomberg/Getty Images

Smoke from the bushfires raging near Sydney in Australia has been blanketing the city in recent weeks, reaching a crisis point on Tuesday when air pollution in parts of the city rose to over 10 times the level deemed hazardous.

Health authorities are warning the public to be careful. Children have been forced to stay indoors during lunchtime at school, ferries were cancelled and office workers were evacuated from buildings as the smoke triggered fire alarms.

These unprecedented conditions have prompted questions over what effect they could have on the population’s long-term health.


Bushfires are so dangerous because they billow fine particulate matter, known as PM2.5, into the air. When this is inhaled, it can go deep into the lungs, where it causes inflammation, and enter the bloodstream to affect other parts of the body.

The link between several hours or days of poor air quality and health problems is well-established. Such exposure can worsen asthma and lung conditions, such as chronic bronchitis, and lead to heart attacks in people with heart disease.

People who are hospitalised or die as a result of poor air tend to have pre-existing respiratory and cardiovascular diseases. Last week, health authorities recorded a roughly 30 per cent increase in ambulance call outs across New South Wales, and hospitalisations for respiratory issues in the area rose by 25 per cent.

Less severe but longer-term exposure, such as the circumstances in Beijing or New Delhi, has been linked to heart, lung and kidney disease, strokes, type 2 diabetes, sepsis and urinary tract infections. It is also associated with smaller babies, miscarriage and stillbirth.

But this isn’t necessarily true of people in Sydney, who typically enjoy relatively unpolluted air.

Fay Johnston at the University of Tasmania, Australia, says that research on a fire in an open-cut coal mine in the south-east of the country in 2014 may shed some light on what to expect.

A community near the mine was exposed to levels of smoke similar to those experienced by the worst-affected parts of Sydney for six weeks. In the years since, Johnston and her colleagues found that children who were more exposed to the smoke while in the womb or in their first two years of life had more respiratory tract infections than those who were less exposed.

Those exposed to more smoke before the age of 2 had stiffer lungs than those who were less exposed, they found.

“But it was a subtle change,” says Johnston. “If there was a kid who was already at high risk – because they had a family history of asthma, or they also lived with smoker, or they had other risk factors – then it might be what tips the balance in getting symptoms.”

A 2017 study of infant rhesus macaque monkeys living near the 2008 California wildfires found something similar: those who were exposed to the smoke had worse lung and immune health at 3 years of age than those who weren’t exposed.

Read more: Measures to reduce air pollution quickly result in big health benefits

Neither study found much evidence that the smoke exposure had lasting effects on the respiratory health of adults, which backs up research suggesting air pollution is worse for developing children.

It may not just be physical health that is affected. The study of around 4000 people living near the coal mine fire found that air pollution exposure was linked to more symptoms of post-traumatic stress disorder in adults two and a half years later.

Calls to the Australian mental health charity Lifeline also spike on days when the bushfires are worst, The Sydney Morning Herald reports.

Linda Selvey of the Royal Australasian College of Physicians says that research on quitting cigarette smoking may help reassure Sydney residents worried about short-term exposure to poor air. “For lung cancer, the risk is never completely eliminated – but gradually the risks [of other health conditions] return to similar levels to people who never smoked,” she says.

The World Health Organization recently found that improving air quality can have quick and dramatic health benefits.

Nevertheless, the air quality in Sydney may continue to be poor in the coming weeks or even months, with the Bureau of Meteorology predicting a longer, hotter summer than normal and fire experts fearing the worst is yet to come.