As wildfires that have already claimed the lives of at least 26 people and billions more animals continue to rage across Australia, health experts say the toxic smoke is also a big cause for concern.

Wildfire smoke poses two major threats to health: lung aggravation and toxicity. When materials such as plastics burn, heavy metals such as lead can catch a ride into the body on smoke particles.

Due to its tiny particle size, once inhaled smoke can travel throughout the bloodstream and wreak havoc on any area of the body, said Stanford University's Dr. Maria Prunicki, a scientist and physician who studied the health effects of Californians' exposure to wildfires.

As Earth's climate heats up, scientists say more wildfires can be expected around the world.

In this image released by the Australian Department of Defence and dated Jan. 7, 2019, smoke and haze hangs over mountains near Cooma, New South Wales from an aircraft conducting damage assessment and surveillance in the bushfire-affected area. (Australian Dept. of Defence/The Associated Press)

The fires in Australia began in September, and the smoke has spread across at least 20 million square kilometres. The air quality rating across Australia is up to 12 times the limit deemed hazardous, and over 20 times higher in certain areas this week.

"That's much higher than anything we've seen in California. The damage is going to be much more severe," Prunicki said in an interview with CBC Radio Quirks & Quarks host Bob McDonald.

Wildfire smoke can contribute to increases in respiratory disorders like bronchitis and asthma as well as heart diseases in those exposed. It can also have adverse effects in pregnancy through pre-term birth and decrease in birth weight.

Prunicki's work looked at the health effects of wildfires in children near Yosemite, a common bushfire site in California. Her research found that after 90 days, those exposed to wildfire smoke had more symptoms of asthma compared with smoke from prescribed burns. It also showed that exposure to wildfires suppressed the regeneration of healthy immune cells.

How humans and animals alike will be affected by Australia’s bushfires 18:16

Last week, the Australian Medical Association (AMA) released a statement warning of potential health hazards from the escalating crisis — both those near active fire zones and those at a distance.

"With denser smoke haze and longer periods that people endure smoke inhalation, there is a much higher risk that previously healthy people will face developing serious illness," Dr. Tony Bartone, AMA's president, said in the statement.

The remains of burnt out buildings are seen along main street in the Australian town of Cobargo, after bushfires ravaged the town. (Sean Davey/AFP/Getty)

The total number of people affected by smoke levels in Australia won't be known for some time. But Dr. Fay Johnston, an associate professor of public health at the University of Tasmania in Australia, said there's a clear, real-time correlation between smoke concentrations and emergency department visits in those regions.

"The number of people who've been affected by this smoke — it's not an isolated event," said Johnston. "It's every major capital city in the country having severe smoke impacts."

Although the long-term health effects of Australia's wildfires are unclear, the public has been urged to limit their exposure and to take extra measures to avoid complications.