Science
Far From the Fires, the Deadly Risks of Smoke Are Intensifying

It kills more people each year than car crashes, war or drugs do. This invisible killer is the air pollution from sources like cars and trucks or factory smokestacks.
But as wildfires intensify and grow more frequent in a warming world, the smoke from these fires is emerging as a new and deadly pollution source, health experts say. By some estimates, wildfire smoke — which contains a mixture of hazardous air pollutants like particulate matter, nitrogen dioxide, ozone and lead — already causes as many as 675,000 premature deaths a year worldwide, as well as a range of respiratory, heart and other diseases.
Research shows that wildfire smoke is starting to erode the world’s progress in cleaning up pollution from tailpipes and smokestacks, as climate change supercharges fires.
“It’s heartbreaking, it really is,” said Dr. Afif El-Hasan, a pediatrician who specializes in asthma care at Kaiser Permanente in Southern California and a board director of the American Lung Association. Wildfires “are putting our homes in danger, but they’re also putting our health in danger,” Dr. El-Hasan said, “and it’s only going to get worse.”
Those health concerns were coming to the fore this week as wildfires ravaged the Los Angeles area. Residents began to return to their neighborhoods, many strewed with smoldering ash and rubble, to survey the damage. Air pollution levels remained high in many parts of the city, including in northwest coastal Los Angeles, where the air quality index climbed to “dangerous” levels.
Los Angeles, in particular, has seen air pollution at levels that could be raising daily mortality by between 5 to 15 percent, said Carlos F. Gold, an expert in the health effects of air pollution at the University of California, San Diego.
That means current death counts, “while tragic, are likely large underestimates,” he said. People with underlying health issues, as well as older people and children, are particularly vulnerable.
The rapid spread of this week’s fires into dense neighborhoods, where they burned homes, furniture, cars, electronics and materials like paint and plastic, made the smoke more dangerous, said Dr. Lisa Patel, a pediatrician in the San Francisco Bay Area and the executive director of the Medical Society Consortium on Climate and Health.
A recent study found that even for homes that are spared destruction, smoke and ash blown inside could adhere to rugs, sofas and drywall, creating health hazards that can linger for months. “We’re breathing in this toxic brew of volatile organic compounds and polycyclic aromatic hydrocarbons and hexavalent chromium,” Dr. Patel said. “All of it is noxious.”
Intensifying and more frequent fires, meanwhile, are upending experts’ understanding of smoke’s health effects. “Wildfire season is no longer a season,” said Colleen Reid, who researches the effects of air pollution from wildfires on heath at the University of Colorado Boulder. “We have fires all year round that affect the same population repeatedly.”
“The health impacts are not the same as if you were exposed once, and then not again for 10 years,” she said. “The effects of that is something that we still don’t really know.”
A United Nations report from 2022 concluded that the risk of devastating wildfires around the world would surge in coming decades. Heating and drying caused by climate change, along with development in places vulnerable to fire, was expected to intensify a “global wildfire crisis,” the report said. Both the frequency and intensity of extreme wildfires have more than doubled in the past two decades. In the United States, the average acreage burned a year has surged since the 1990s.
Now, pollution from wildfires is reversing what had been a decades-long improvement in air quality brought about by cleaner cars and power generation. Since at least 2016, in nearly three-quarters of states in the U.S. mainland, wildfire smoke has eroded about 25 percent of progress in reducing concentrations of a type of particulate matter called PM 2.5, a Nature study in 2023 found.
In California, wildfire smoke’s effect on air quality is offsetting public health gains brought about by a decline in air pollution from automobiles and factories, state health officials have found. (By releasing carbon dioxide and other planet-warming gases into the atmosphere, wildfires are themselves a big contributor to climate change: The wildfires that ravaged Canada’s boreal forests in 2023 produced more greenhouse gases than the burning of fossil fuels in all but three countries.)
”It’s not a pretty picture,” said Dr. Gold of U.C. San Diego, who took part in the Nature study. If planet-warming gas emissions continue at current levels, “we’ve got some work that suggests that mortality from wildfire smoke in the U.S. could go up by 50 percent,” he said.
One silver lining is that the Santa Ana winds that so ferociously fueled the flames in recent days have been blowing some of the smoke toward the ocean. That stands in contrast to the smoke from the 2023 Canadian wildfires that drifted to New York and other American states hundreds of miles away, causing spikes in emergency room visits for asthma.
At one point that year, more than a third of Americans, from the East Coast to the Midwest, were under air quality alerts from Canadian wildfire smoke. “We’re seeing new and worsening threats in places that are not used to them,” Dr. Patel, the pediatrician, said.
The new normal is bringing about changes to health care, Dr. Patel said. More health systems are sending out air quality alerts to vulnerable patients. In the small community hospital where she works, “every child that comes in with wheezing or asthma, I talk to them about how air pollution is getting worse because of wildfires and climate change,” she said.
“I teach them how to look up air quality, and say they should ask for an air purifier,” Dr. Patel added. She also cautions that children should not participate in cleanup after a wildfire.
Scientists are still trying to understand the full range of wildfire smoke’s health effects. One big question is how much of what researchers know about vehicle exhaust and other forms of air pollution apply to wildfire smoke, said Mark R. Miller, a researcher at the Center for Cardiovascular Science at the University of Edinburgh who led a recent global survey of climate change, air pollution and wildfires.
For example, exhaust particles “are so small that when we breathe them in, they go deep down into our lungs and are actually small enough that they can pass from our lungs into our blood,” he said. “And once they’re in our blood, they can be carried around our body and start to build up.”
That means air pollution affects our entire body, he said. “It has effects on people who have diabetes, has effects on the liver and the kidney, it has effects on the brain, on pregnancy,” he said. What’s still not clear is whether pollution from wildfires has all of those same effects. “But it’s likely,” he said.
Experts have a range of advice for people living in areas with smoke. Keep an eye on air quality alerts, and follow evacuation orders. Stay indoors as much as possible, and use air purifiers. When venturing outside, wear N95 masks. Don’t do strenuous exercise in bad air. Keep children, older people and other vulnerable groups away from the worst smoke.
Ultimately, tackling climate change and cutting back on all kinds of air pollution is the way to reduce the overall burden on health, said Dr. El-Hasan of the American Lung Association. “Can you imagine how much worse things would be if we hadn’t started cleaning up emissions from our cars?” he said. “I’m trying to think, glass half full, but it does break my heart and it does worry me.”

Science
Bird flu infections in dairy cows are more widespread than we thought, according to a new CDC study

A new study published by the U.S. Centers for Disease Control and Prevention shows that the H5N1 bird flu virus is probably circulating undetected in livestock in many parts of the country and may be infecting unaware veterinarians.
In the health agency’s Morbidity and Mortality Weekly Report, a group of researchers from the CDC, the Ohio Department of Health and the American Assn. of Bovine Practitioners, reported the results of an analysis they conducted on 150 bovine, or cow, veterinarians from 46 states and Canada.
They found that three of them had antibodies for the H5N1 bird flu virus in their blood. However, none of the infected vets recalled having any symptoms — including conjunctivitis, or pink eye, the most commonly reported symptom in human cases.
The three vets also reported to investigators that they had not worked with cattle or poultry known to be infected with the virus. In one case, a vet reported having practiced only in Georgia (on dairy cows) and South Carolina (on poultry) — two states that have not reported H5N1 infections in dairy cows.
Seema Lakdawala, a microbiologist at Emory University in Atlanta — who was not involved in the research — said she was surprised that only 2% of the veterinarians surveyed tested positive for the antibodies, considering another CDC study showed that 17% of dairy workers sampled had been infected. But she said she was even more surprised that none of them had known they were infected or that they had worked with infected animals.
“These surprising results indicate that serum surveillance studies are important to inform risk of infections that are going undiagnosed,” she said. “Veterinarians are on the front line of the outbreak, and increased biosafety practices like respiratory and eye protection should reduce their exposure risk.”
Jennifer Nuzzo, director of the Pandemic Center at Brown University, described the study as a “good and bad news story.”
“On one hand, we see concerning evidence that there may be more H5N1 outbreaks on farms than are being reported,” she said. “On the other hand, I’m reassured that there isn’t evidence that infections among vets have been widespread. This means there’s more work that can and should be done to prevent the virus from spreading to more farms and sickening workers.”
The analysis was conducted in September 2024. At that time, there had been only four human cases reported, and the infection was believed to be restricted to dairy cattle in 14 states. Since then, 68 people have been infected — 40 working with infected dairy cows — and the virus is reported have infected herds in 16 states.
John Korslund, a retired U.S. Department of Agriculture scientist, said in an email that finding H5N1 antibodies in the blood of veterinarians was an interesting “but very imprecise way to measure state cattle incidence.” But it underscored “that humans ARE susceptible to subclinical infections and possible reassortment risks, which we already knew, I guess.”
Reassortment occurs when a person or animal is infected with more than one influenza virus, allowing the two to mingle and exchange “hardware,” potentially creating a new, more virulent strain.
More important, he said, the D1.1 version of the strain — which has been detected in Nevada dairy cattle and one person living in the state — is “changing the landscape. … [P]eople may be more more susceptible (or not) with a greater potential for severeness (or not).”
“I’m confident that we’ll find it in other states. Its behavior and transmissibility within and between cattle herds is still pretty much a black box,” he said.
Science
Top N.I.H. Official Abruptly Resigns as Trump Orders Deep Cuts

The No. 2 official at the National Institutes of Health abruptly resigned and retired from government service on Tuesday, in another sign that the Trump administration is reshaping the nation’s public health and biomedical research institutions.
The official, Dr. Lawrence A. Tabak, a dentist and researcher, was long considered a steadying force and had weathered past presidential transitions. In a letter that Dr. Tabak sent to colleagues on Tuesday, he did not give a reason for his decision. One person familiar with the decision said Dr. Tabak had been confronted with a reassignment that he viewed as unacceptable.
“It has been an enormous privilege to work with each of you (and your predecessors) to support and further the critical NIH mission,” Dr. Tabak wrote.
Dr. Tabak resigned at a turbulent time for the institutes, the nation’s premier biomedical research industry, composed of 27 separate institutes and centers that study and develop treatments for diseases like cancer and heart conditions as well as infectious diseases like AIDS and Covid. The N.I.H. spends roughly $48 billion a year on medical research, much of it in grants to medical centers, universities and hospitals across the country.
President Trump’s decision to slash billions of dollars in N.I.H. grant funding has sparked a bitter court battle. And the Senate on Wednesday voted to advance the nomination of Robert F. Kennedy Jr., a vaccine skeptic and the president’s pick for secretary of the Department of Health and Human Services, which oversees the N.I.H.
Mr. Kennedy has said he would cut 600 N.I.H. jobs.
The N.I.H. said it would soon have a statement about Dr. Tabak’s decision.
Dr. Tabak was not well-known to the public. But his decision to leave is surprising, and destabilizing for an agency that is on the political hot seat. He was viewed as someone who could work across party lines; he had survived the presidential turnovers of both parties and had indicated he expected to stay on after Mr. Trump was elected in November.
Ordinarily, Dr. Tabak would have ascended to the job of acting N.I.H. director during the transition from one administration to the next. But the Trump administration installed another researcher, Matthew Memoli of the National Institute of Allergy and Infectious Diseases, as acting director. Dr. Memoli criticized Covid vaccine mandates, as did Mr. Kennedy.
As acting director of the N.I.H. last year, Dr. Tabak pushed back against Republicans’ assertions that a lab leak stemming from U.S. taxpayer-funded research might have caused the coronavirus pandemic. He told lawmakers that viruses being studied at a laboratory in Wuhan, China, bore no resemblance to the one that set off the world’s worst public health crisis in a century.
Ellen Barry contributed reporting.
Science
California’s Scary Product Warning Labels Might Be Working, Study Says

The warnings, on thousands of products sold in California, are stark.
“Use of the following products,” one label says, “will expose you to chemicals known to the State of California to cause cancer, birth defects or other reproductive harm.”
Now, new research shows the warnings may be working.
A study published Wednesday in the journal Environmental Science & Technology found that California’s right-to-know law, which requires companies to warn people about harmful chemicals in their products, has swayed many companies to stop using those chemicals altogether.
As it turns out, companies don’t want to sell a product that carries a big cancer warning label, said Dr. Megan Schwarzman, a physician and environmental-health scientist at the University of California, Berkeley School of Public Health and an author of the study.
Combine that with the threat of lawsuits and reputational costs, as well as companies just wanting to do the right thing for health, and “it becomes a great motivator for change,” she said.
California maintains a list of about 900 chemicals known to cause cancer and other health effects. Under the 1986 right-to-know law, also known as Prop 65, products that could expose people to harmful amounts of those chemicals must carry warning labels.
Critics had long mocked the measure, saying the warnings were so ubiquitous — affixed to cookware, faux leather jackets, even baked goods — that they had become largely meaningless in the eyes of shoppers. But the latest study found that companies, more than consumers, may be most influenced by the warnings.
To assess the law’s effect, researchers carried out interviews at 32 global manufacturers and retailers that sell clothing, personal-care, cleaning, and a range of home products. Almost 80 percent of interviewees said Prop 65 had prompted them to reformulate their products.
Companies can avoid the warning labels if they reduce the level of any Prop 65 chemicals below a “safe harbor” threshold.
A similar share of companies said they looked to Prop 65 to determine which chemicals to avoid. And 63 percent said the law had prompted them to also reformulate products they sold outside California.
The American Chemistry Council, which represents chemical manufacturers, did not immediately respond to a request for comment on the study.
No other state has a law quite like Prop. 65, requiring warnings on such a wide range of products about cancer or reproductive harm. New York enacted a more limited law in 2020 that requires manufacturers to disclose certain chemicals in children’s products and that bans the use of certain chemicals by 2023. Other states have laws geared toward disclosure of ingredients on labels.
California, meanwhile, is pushing ahead. A 2018 change to Prop 65 has meant products are starting to carry even more specific labels. Some food and beverage cans, for example, may carry labels that warn that they “have linings containing bisphenol A (BPA), a chemical known to the State of California to cause harm to the female reproductive system.”
The latest research is part of a larger effort to analyze Prop 65’s effect on people’s exposure to toxic chemicals. In a study published last year, researchers at the Silent Spring Institute and UC Berkeley found that in the years after certain chemicals were listed under the law, levels of those chemicals in people’s bodies decreased both in California and nationwide.
That research came with a caveat, however. In some examples where levels of a listed chemical decreased, a close substitute to that chemical, potentially with similar harmful effects, increased. Prop 65 has no mechanism to check the safety of alternative chemicals.
It suggested that stronger policies were needed at both the federal and state levels to study and regulate the thousands of chemicals on the market, Dr. Schwarzman said. “This is so much bigger than the individual consumer and what we choose off-the-shelf,” she said.
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