Exposure to toxic pollutants may increase the risk of developing devastating neurological conditions, a study suggests.
Researchers in Sweden evaluated 1,000 patients diagnosed with amyotrophic lateral sclerosis (ALS), a terminal neurodegenerative disease that attacks neurons in the brain and spinal cord responsible for motor functions.
Also called Lou Gehrig’s disease and motor neuron disease in the UK, ALS affects about 30,000 Americans and kills in just two to five years as the neuron damage attacks the body’s ability to move, eat and breathe. About 5,000 die every year.
The causes are largely unknown, but recent research suggests environmental contaminants could lead to inflammation that attacks neurons in the brain and spinal cord.
In the new study, researchers compared ALS patients both to siblings and healthy controls and tracked their exposure over 10 years to the pollutants PM2.5, PM10 and nitrogen dioxide.
PM2.5 are a group of microscopic particles that are emitted directly into the air from fossils fuels burned from factories and gasoline-powered stoves and cars, as well as burning wood in fireplaces. These can penetrate deep into the lungs and bloodstream, while PM10, which includes dust and pollen, infiltrates the airways.
Nitrogen dioxide, meanwhile, is a gas that comes from burning fossil fuels.
The team found exposure to even small amounts of pollutants over the course of 10 years increased the risk of developing ALS by up to 30 percent. Additionally, the likelihood of the disease progressing more quickly went up by 34 percent.
A new study out of Sweden suggests air pollution may raise the risk of developing amyotrophic lateral sclerosis (ALS) by up to 30 percent. Pictured above is the Los Angeles skyline covered in smog in December 2024
While the exact mechanism is unclear, experts believe PM2.5, PM10 and nitrogen dioxide may induce harmful inflammation in the brain and spinal cord. They have also been shown to weaken protective layers in the brain, leaving neurons vulnerable to damage.
Importantly, the researchers looked at Sweden, which is one of the World Health Organization’s top cleanest first-world countries in terms of air quality. Experts estimate the air in Sweden is about 12 percent cleaner than in the US and that the US has 59 percent more air pollution per capita than Sweden.
Sweden has also reduced greenhouse emissions by about 60 percent since 1990.
The findings suggest that there may be even more drastic health effects in the US population. The US is the 116th most polluted country in the world, according to IQ Air, while Sweden ranks 12th.
Jing Wu, study author and researcher at the Institute of Environmental Medicine of Karolinska Institutet, said: ‘We can see a clear association, despite the fact that levels of air pollution in Sweden are lower than in many other countries.
‘This underlines the importance of improving air quality.’
The American Lung Association estimates 156 million Americans, just under half, were exposed to unhealthy levels of air pollution every day in 2025, 25 million more than the year before in 2024.
The study, published Tuesday in the journal JAMA Neurology, looked at 1,463 Swedish participants who had recently been diagnosed with ALS and compared them to 1,768 siblings and 7,310 matched controls from the general population.
The average age for ALS patients and controls was 67, and 56 percent of participants across all groups were men.
Using machine learning, satellite and meteorological data and traffic information, researchers analyzed levels of pollutants PM2.5 and PM10, along with nitrogen dioxide at participants’ home addresses going back 10 years.
Actor Eric Dane (pictured here in 2024) announced his ALS diagnosis early last year. He said he initially experienced weakness in his right hand
Famed physicist Stephen Hawking (pictured above) lived with ALS for over 50 years, significantly longer than the typical five-year life expectancy
The team found that even at low levels, long-term air pollution exposure was linked to a 20 to 30 percent higher risk of developing ALS. And after 10 years, PM2.5 exposure was associated with a 34 percent increased risk of ALS progressing faster. The risk was 30 percent greater for PM10.
Caroline Ingre, study author and adjunct professor at Karolinska Institutet’s Department of Clinical Neuroscience, said: ‘Our results suggest that air pollution might not only contribute to the onset of the disease, but also affect how quickly it progresses.’
The team suggested air pollution may cause inflammation and oxidative stress, an imbalance of toxic free radicals, in the nervous system, which attacks neurons and causes proteins to become misfolded or defective.
Pollution may also weaken the blood-brain barrier, a protective layer lining the brain’s small blood vessels called capillaries. This allows toxins to reach the brain more easily and damage neurons.
The researchers cautioned that the findings are observational, so they do not establish a firm connection between pollution and ALS.
Air pollution has also been linked to several other health conditions. A 2024 study, for example, suggested pollution exposure in the womb or early childhood may raise the risk of autism due to inflammation and oxidative stress.
A 2025 study, meanwhile, suggested that people living in areas ravaged by wildfires, a major source of pollution, may be at a greater risk of mental health disorders like depression and psychosis, which is likely also due to inflammation.
