New Study Finds Microplastics Can Cross Blood-Brain Barrier

Microplastics are infiltrating our brains, a new study finds. And the effects should sound an alarm about a global threat to human health, says the study’s lead author.

In the sign-of-the-times 1967 movie The Graduate, plastics were hailed as the future. Now, thanks to an agglomeration of recent medical studies and environmental reports, pollution of the petrochemical product has been called out as a “pervasive and growing threat” to the planet’s overall health, as a landmark 2023 United Nations Environment Programme report warns.

Most plastic does not biodegrade but breaks down into ever-smaller particles: Microplastics are bits smaller than 5 millimeters in one dimension; nanoplastics are even tinier, about 1 micron in size. Microplastics now permeate our environment: They have been detected in crustaceans from the deepest, darkest part of the Pacific Ocean, the Mariana Trench, and atop Mount Everest. They end up in our water and food and then inside us.

In recent years, microplastics have been discovered in various parts of human bodies — hearts, livers, lungs, and even blood and bone marrow. A study published in 2021 reported the first evidence of microplastics in a human placenta, and other studies have detected it in baby poop.

The new study, in Nature Medicine, is the first to find that microplastics have passed through the protective blood-brain barrier and into our brains.

Researchers from the University of New Mexico (UNM) and their associates used a combination of scanning electron microscopy, transmission electron microscopy, and polarization wave microscopy to detect and characterize microplastics in brain tissue samples.

Beyond the alarming presence of microplastics, the scientists found that the amounts in the brain samples had increased significantly over time. Samples collected in 2024 contained about 50 percent more microplastics than those taken eight years earlier.

The 2024 samples held about 7 grams of microplastics — the equivalent of a plastic spoon in weight.

“[Our brains] today are 99.5 percent brain, and the rest is plastic,” says co-lead author Matthew Campen, PhD, MSPH, a professor of toxicology at UNM.

“That would mean that our brains today are 99.5 percent brain, and the rest is plastic,” says co-lead author Matthew Campen, PhD, MSPH, a professor of toxicology at UNM.

These plastic particles may play a role in dementia. Brain tissue from people who had been diagnosed with dementia had up to 10 times more plastic than others, he says. While there is a clear correlation, the study did not prove whether higher levels of plastic in the brain caused dementia, says Campen.

“Right now, it is premature to say there are health effects being caused by plastics: We simply don’t have quality data to make this conclusion,” he explains. “However, there are several health trends that are global and occurring over the past decade or two that give us reasons for concern. Also, if the concentration of plastics continues to rise, we are uncertain if there will be a threshold at some point in the future where problems occur.”

Campen says plastics may get into our brains by “hijacking” fats from our food and hitching a ride through the brain-blood barrier. Beyond their intrinsic dangers, the microplastics can also act as carriers for other chemicals, such as toxic additives used in making the plastics and environmental pollutants they might absorb.

The study quantified 12 different plastic polymers in the brain tissue; the most common was polyethylene, which is widely used for food packaging and containers, such as bottles and cups.

“We need a comprehensive solution to managing the generation, distribution, and waste management to ensure that micro- and nanoplastics are not allowed to continually increase globally,” he says. “This will take strong leadership and international cooperation.”

The good news, however, is that our body may ultimately be able to rid itself of at least some of this plastic.

“Our data also suggest that the amount of microplastics does not simply accumulate as we age, but probably gets cleared by our bodies, even if slowly,” Campen says. He also says that his lab’s method of detection is still being optimized by researchers worldwide, and the numbers may change as the analysis is refined.

He calls for action to protect us from the plastic threat.

“We need a comprehensive solution to managing the generation, distribution, and waste management to ensure that micro- and nanoplastics are not allowed to continually increase globally,” he says. “This will take strong leadership and international cooperation.”

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