What are the long-term health effects of bushfire smoke?

8 minute read

While prolonged exposure to bushfire smoke is certainly harmful, the extent of that health damage is as hazy as the skies

Australia has faced unprecedented bushfires this summer. Millions of hectares have been burnt, thousands of houses razed and an estimated one billion animals may have been killed.

Tragically, dozens of people have died in the fires already. As smoke turns the sun red and blankets towns and cities, many may be wondering whether they, too, will suffer health consequences down the track.

The dangers of bushfire smoke inhalation are clear in the short-term. For the healthy, the smoke may bring some eye and throat irritation. But for those with underlying conditions, the consequences may be far more severe.

Bushfire smoke has been linked to more frequent and more intense symptoms among people with respiratory and cardiovascular issues, a greater need for asthma medication and more visits to a GP or other healthcare provider.

People are more likely to be admitted to the emergency department for respiratory conditions and cardiovascular problems such as cardiac arrest. In NSW alone, emergency presentations for asthma and breathing difficulties have jumped 30%.

More bushfire smoke also leads to more deaths.

To quantify the risk, Associate Professor Fay Johnston and her colleagues at the Centre for Air pollution, Energy and Health Research (CAR) analysed the effect that bushfire and hazard reduction burns had on the health of Sydneysiders between 2001 and 2013.

That period had 184 extremely smoky days, and these caused an estimated 197 extra premature deaths, 436 cardiovascular hospitalisations and 787 respiratory hospitalisations, according to their 2018 paper in the MJA.

One of the most harmful components of bushfire smoke is the particulate matter suspended in the haze. These can be made up of organic and inorganic carbon, among other compounds.

Research has focused on the impact of fine particulate matter, known as PM2.5 because it is smaller than 2.5 micrometres in diameter. In context, a human hair is around 70 micrometres. While larger particles get trapped in the nose, mouth or throat, these are so small that they can get deep into the lungs, and even the bloodstream. These cause inflammation, and affect people’s cardiovascular and respiratory systems and metabolic functions.


So what can you do?

If you don’t know exactly what to do to combat breathing in bushfire smoke, you’re not alone.

Face masks are flying off the shelves, but many experts are advising people not to buy them. So what’s the answer?

Wearing surgical masks is almost certainly a waste of time as they are designed to prevent harmful microbes from travelling from a healthcare worker into a vulnerable patient, says Professor Guy Marks, respiratory physician and epidemiologist at UNSW.

There is debate about the more specialised P2 and N95 masks. While some say these may be effective because they can filter out PM2.5, Professor Marks warns  they must have a seal around the nose and mouth, or they won’t be effective – meaning people with facial hair and sideburns may be out of luck. The masks may not seal properly around a smaller face either.

Even if these masks do work, which is unclear at present, that effectiveness will only be for a limited period of time.

“They are not designed for long-term protection from smoke. They would need to be completely redesigned if they were to be effective for that purpose,” Professor Marks says.

In fact, they can make it harder for people to breathe, which may be a problem for people with pre-existing lung disease or women who are pregnant.

Professor Fay Johnston says that while the evidence base is limited at present, high risk groups such as pregnant women and young children may benefit from HEPA (high-efficiency particulate air) filters for their house.

“You can put one in your bedroom and you’ve got a clean air haven in your room. You don’t need to disrupt your life, go to the library or put a mask on,” she says. “And you can sleep in the room and reduce your exposure hugely.

Experts do agree that the best thing to do is to stay indoors, with the windows and doors closed, in air-conditioned buildings (if possible), and to avoid unnecessary vigorous outdoor activity.


But bushfire smoke also includes gases such as carbon monoxide and dioxide, nitrogen dioxide and sulphur dioxide. It also includes polycyclic aromatic hydrocarbons (PAHs), such as those given off when you barbeque meat.

These are some of the reasons hospital admissions for asthma are greater when the air pollution is from bushfire smoke than it is from traffic pollution, says Professor Johnston.

“That tells us that, for the lungs at least, it’s probably more irritating,” she says.

Recent studies from Japan and the US have found that short-term PM2.5 exposure at levels within the WHO air quality guidelines are still linked to deadly cardiac arrests and hospital admissions heart and lung diseases, diabetes, Parkinson’s disease, sepsis, kidney failure, UTIs and skin infections . 

What we know and what we don’t

But it’s not really clear what effect weeks or even months of bushfire smoke will have on people.

The WHO estimates that ambient air pollution is responsible for more than four million deaths globally each year. Chronic exposure to poor air is linked to smaller babies, preterm birth, and developmental issues such as diabetes and neurological issues in children. In adults, it is linked to reduced lung function, respiratory issues, cardiovascular and cardiopulmonary disease and cancer.

But this research, which typically captures city smog and pollution, doesn’t necessarily reflect what is happening in Australia, where the air quality is relatively good the rest of the time.

“This is a huge, continental-scale event, and there are a lot of gaps in our knowledge,” says Professor Johnston.

To get an idea of the effect of medium-term exposure, experts turn to research on the Californian wildfires, and the Hazelwood mine fire here in Australia. 

The authors of a 2017 study of infant rhesus monkeys found that those who were exposed to smoke from the 2008 Californian wildfires had poorer lung and immune health at three-years-of-age than their peers who weren’t exposed.

Similarly, Associate Professor Rebecca J. Schmidt at the University of California Davis School of Medicine is studying the effects of several Californian wildfires on women who were pregnant at the time.

“Most commonly reported by mums was stress and anxiety, and we saw that this was at a higher level right away – but it also persisted out a year later for many of these mums. Around 20% were experiencing stress and anxiety a year later,” says Schmidt.

While the research is still under way, the preliminary data shows that respiratory conditions in both the adult women and children who experienced the smoke had returned to relatively normal levels after four to five months, she says.

The effects of the Hazelwood open-cut coal mine fire in 2014 may also shed some light on what to expect. Professor Johnston and her colleagues have been studying the long-term effects of living near the six-week-long fire on around 40,000 community members’ mental and physical health.

Adults continued to have higher rates of respiratory symptoms even a year after the fire, and children under the age of two or in the womb during the fire also had higher rates of respiratory tract infections around three years after the fire.

Children who were more exposed to the smoke had slightly stiffer lungs and slightly stiffer blood vessels than those that were less exposed, says  Professor Johnston. The findings were small however, and may not be clinically meaningful.

“We saw the same things in kids who lived with a smoker in the house, or whose mother might have smoked during pregnancy,” she says. The combination of bushfire and cigarette smoke exposure had more of an effect, they found.

Psychological health is also affected. PTSD symptoms were more common among people more exposed to the smoke even two and a half years later.

When asked if there could be similar psychological fallout from the bushfires, Professor Johnston says she has “no doubt” this would be the case.

“It’s very stressful. Apart from the fact that it is horrible, you don’t see the sun and your eyes are irritated, there are probably biological pathways [due to the inflammation caused by fine particulate matter travelling through the brain and body] that increases psychological symptoms as well,” she says.

While some have compared breathing the air on the worst days of bushfire haze in Sydney as the equivalent of smoking 30 cigarettes a day, it’s not clear how similar this really is to bushfire smoke inhalation. And we do know that cigarette smokers’ lungs show dramatic improvements once they quit.

For now, experts can only hope that many questions around the effects of bushfire smoke may be answered thanks to $5 million in funding announced by Health Minister Greg Hunt for research into the physical and mental health effects of this hazard.

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