Los Angeles has experienced some of the world’s worst air quality this week as smoke from massive wildfires blankets the region and threatens the health of far more people than the fires themselves. And that will end up adding to the economic toll.

Almost 180,000 have been forced to flee their homes and at least 10,000 structures have been destroyed or damaged. The fires are projected to cause $20 billion in insured losses, according to JPMorgan Chase & Co analysts. That damage projection doesn’t even factor in the likely high health impacts of the smoke, which cause an estimated billions in hidden health-linked costs in the U.S. annually.

It’s hard to overstate just how dangerous wildfire smoke is. “There are many pollutants of concern in wildfire smoke,” including ozone, carbon monoxide and other toxic gases, says Debra Hendrickson, a pediatrician in Reno who wrote the book "The Air They Breathe about how climate change threatens children’s health. Small particles in the smoke, called particulate matter 2.5 or PM2.5 — and even smaller ultra-fine particles known as PM0.1 — also pose a threat in large part because they can penetrate deep into the lungs, “enter the bloodstream, and reach every organ of the body,” says Hendrickson.

Most of the research on the dangers of human exposure to PM2.5 is based on pollution released from burning fossil fuels. But newer research suggests wildfire smoke particulates are just as hazardous, if not more so.

What is certain is that wildfire smoke exposure can cause myriad respiratory problems, according to Catharine Guidice, an emergency physician and climate change and human health fellow at Harvard University’s FXB Center. It can also increase susceptibility to respiratory diseases, such as Covid-19, influenza, RSV and pneumonia.

There’s also a host of potential long-term impacts from increased dementia risk to pregnancy complications. “We see that children that were exposed to wildfire smoke in utero are born at preterm at higher rates. They have lower birth weights,” says Carlos Gould, an environmental health scientist at the University of California, San Diego.

He adds that smoke can even kill. The higher pollution levels seen in parts of Los Angeles, for example, may increase mortality by between 5% to 15% on the day people are exposed, and “that doesn’t account for lagged effects,” Gould says.

In other words, because of all the smoke, “we’re going to be seeing worsened respiratory health [and] higher mortality in the coming days and weeks,” he says. “That’s a particular concern with people with underlying respiratory conditions, underlying cardiovascular conditions, the elderly, children and pregnant women.”

These health impacts are a hidden cost of wildfires that play out in emergency rooms, lost days of work and long-term care. A 2023 study in the journal Science of The Total Environment projects that PM2.5 from smoke alone could cause 4,000 premature deaths annually, corresponding to $36 billion in health-related losses in the U.S. Another study in the same journal looking at wildfire smoke in the U.S. between 2008 and 2012 put the long-term costs at between $76 billion and $130 billion in 2010 dollars. One reason wildfire smoke has such a large impact is that it spreads far beyond the immediate vicinity of the flames.

“The big challenge about smoke is it gets blown around,” says Gould. This means those close to a fire may not experience much smoke at all, while those far from flames may be most impacted. That was on display in 2023 when wildfire smoke traveled from Canada and descended on New York and other parts of the East Coast.

The widespread smoke during Australia’s 2019 to 2020 wildfire season caused nearly A$2 billion ($1.2 billion) in healthcare costs, according to a Nature Sustainability study. Much of that was driven by hospital visits for respiratory diseases and cardiovascular problems, as well as an estimated 429 smoke-related premature deaths.

Gould recommends that individuals monitor local air quality regularly to lower their risk of smoke inhalation. The website AirNow uses an official U.S. color-coded index to identify if the air quality is healthy (green) or not (red and purple). The iPhone also includes air quality information in the Apple weather app.

When going outside in smoke is unavoidable, Hendrickson recommends wearing a high-quality mask, such as an N95. For young babies who can’t wear masks, she advises draping a damp blanket over a car seat as an adult is nearby to ensure the blanket is not directly on the child’s face. Additionally, she suggests having a standalone air purifier or air filter-equipped HVAC system to help keep indoor air quality at healthy levels.

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