When the San Francisco Bay Area experienced a record 30 consecutive days of worrisome air quality alerts in August and September, Mary Prunicki began taking blood samples from firefighters.
And the damage isn't likely to have stopped there. Prunicki, director of air pollution and health research at Stanford University's Sean N. Parker Center for Allergy and Asthma Research, is studying the blood samples to understand what wildfire smoke does to human health. It's part of a growing body of work that illustrates how wildfire seasons made worse by climate change threaten not just immediate destruction but also long-term health.
She and other scientists are particularly concerned about a type of particulate matter in wildfire smoke known as PM2.5. These tiny airborne particles, about one-twentieth the width of a human hair, are especially dangerous because they can be breathed deeply into the lungs.
"The size of that particulate can, when you inhale it, go all the way to the base of your lungs and then cross over into your bloodstream," Prunicki said. “Once it's in the bloodstream, it can go to various organs and do all kinds of damage."
Experts have said that in a warming world, devastating wildfires like the ones that tore across California, Oregon and Washington last year will be more common. Around the world, wildfire seasons have been starting earlier and lasting longer, becoming in some regions an almost year-round threat.
In addition to being more frequent, studies have shown that climate change is making the blazes more intense and destructive.
The results of Prunicki's study are forthcoming, but a clearer picture is emerging of just how damaging wildfire smoke can be to humans, and scientists are sounding the alarm over a problem they say is only going to get worse with climate change.
"In the climate science community, we've been predicting these types of impacts for decades now," said Tom Corringham, an environmental economist at the Scripps Institution of Oceanography at the University of California, San Diego.
Corringham co-authored a study published last month in the journal Nature Communications that found that airborne particles in wildfire smoke can be several times more harmful to human respiratory health than other forms of air pollution, including car exhaust.
It's not yet well understood why wildfire smoke is more harmful than other forms of ambient air pollution, although it is likely to have something to do with the chemical composition of what's being burned, Prunicki said. Wildfires that engulf homes and other buildings, for instance, can be particularly dangerous because the chemicals in furniture, clothing and other everyday items are released. In some cases, the materials in firefighters' protective gear can also release harmful particulate matter.
Tony Stefani, a retired San Francisco fire captain, knows the risks well. Stefani, who in 2006 founded the San Francisco Firefighters Cancer Prevention Foundation, was diagnosed with a rare form of kidney cancer. He recalled wondering whether his illness was somehow linked to his line of work.
"I knew there was definitely something wrong," Stefani said. "And I thought there was a direct correlation between what I had and my exposures on the job."
Many of his colleagues, Stefani said, accept that developing cancer is not a matter of if but when. Studies by the National Institute for Occupational Safety and Health have shown that firefighters are at higher risk of cancer and cancer-related deaths compared to the general population, but researchers want to know why — and how best to protect them.
Through his foundation, Stefani works to spread the word about early detection and prevention, but he's also involved with scientific efforts such as Prunicki's research to better understand how exactly wildfire smoke affects immune functioning and human health.
While firefighters are among the most vulnerable when it comes to smoke exposure, it's not just those on the front lines battling blazes who are feeling the impacts of more frequent and intense wildfires.
Studies have observed increases in hospitalizations, particularly for respiratory conditions, during wildfire events. In their study, Corringham and his colleagues combed through 14 years of hospital admissions records in Southern California, analyzing them together with satellite data on wildfire smoke and wind.
The researchers discovered that an increase of PM2.5 pollution from wildfire smoke caused respiratory-related hospital admissions to increase by 1.3 percent to 10 percent. An increase in PM2.5 from other sources of air pollution, on the other hand, contributed to only a 1 percent rise in hospital admissions.
Their findings suggest air quality standards may need to take into account differences in toxicity between different forms of air pollution, said a co-author of the study, Rosana Aguilera, a postdoctoral researcher at the Scripps Institution of Oceanography.
"If there are different impacts of PM2.5 on health, depending on where this PM2.5 is coming from, then we should study that further and reflect that in standards and policies for air pollution," she said.
A study published Wednesday in the journal JAMA Dermatology also found that wildfire smoke can exacerbate more than just respiratory conditions. Researchers at the University of California, San Francisco observed a rise in the number of patients visiting health clinics for eczema and other general skin concerns in November 2018, when the catastrophic Camp Fire raged in Northern California.
The scientists found that even short-term exposure to hazardous particulate matter in wildfire smoke can have consequences for skin health.
The studies of the health effects of wildfire smoke paint a concerning picture of a future in which climate change is expected to supercharge wildfire seasons.
That realization, Stefani said, makes his foundation's collaboration with scientists all the more important, because science can help advocates push for safer working conditions and better public health measures.
"They're the impetus for change," Stefani said of the studies. "That is the reason that we know there's a problem. When we have the scientific proof that something's wrong and we have the numbers to show it, change can occur. And that's really, really important."