A Study in Mice Finds the Brain’s Immune Cells Gorging on Plastic

We’re not Barbie girls, but we live in a plastic world.

Microplastics, tiny specks of broken-down plastic, are all around us. They hover in the air, float in our water, and are sprinkled in the food we eat. These particles have even been detected in relatively pristine ice sheets in Antarctica—a continent with minimal human presence.

They’re also inside our bodies. Microplastic dust lingers in our liver, kidney, blood, and reproductive cells. As their levels build up, microplastics stress normal cell functions, triggering inflammation and hormonal problems. In a small number of people, they’re linked to an increased risk of heart attack, neurological problems, and stroke. A recent preprint analyzing donated brain tissue from deceased people detected large amounts of microplastics in their brains, especially around their blood vessels.

Now, a new study sheds light on one way these pesky particles may be detrimental to brain health. By tracking microplastics in the brains of mice, the team found they damaged the brain’s immune cells. These protective cells accumulated microplastics, instead of digesting them, and then the damaged cells clumped up in the brain’s blood vessels, eventually blocking normal blood circulation—with consequences. Mice given a small dose of microplastics struggled to walk and had a slightly harder time remembering places, even a month later.

Food aside, many current medical devices are made of plastic, which ultimately wears down and could potentially directly leak the particles into a patient’s bloodstream. Though the findings need replication in humans—our blood vessels are larger than mice’s—they do offer “a focused direction for understanding the potential health risks associated with microplastics,” wrote the authors.

Friend or Foe?

Picture your daily morning routine. Now, mentally scan for all the plastic involved.

It’s everywhere. There’s the coffee pot collecting a drip brew or a Keurig pod to get the day going, the shampoo and conditioner container as you shower, the jug that holds orange juice or milk, and the leftovers in a plastic container, ready for a quick zap in the microwave.

Plastic is so prevalent it’s difficult to imagine a world without the material. But its large-scale production only ramped up in the 1950s, after World War II. During the war, the innovative material was used to craft lightweight yet durable radar and radio devices, ammunition, and disposable medical tools. From there, it trickled down into everyday use.

This came at an environmental cost. Made of synthetic molecules—often derived from fossil fuels—plastics are notoriously difficult to break down. As of 2015, humans had generated approximately 6.3 billion metric tons of plastic waste, just nine percent of which had been recycled. By 2050, roughly double that amount will load up landfills. Despite efforts at recycling or making biodegradable plastics, most products end up in landfills or our environment—either on land or in waterways and oceans.

The latter is especially concerning. As plastics wear down, they shed tiny specks that marine life ingests. Roughly the size of a sesame seed, these floating toxins are gulped up by plankton—which larger marine animals feed on—oysters, scallops, and other ocean creatures. The contamination eventually moves up the food chain and reaches seafood lovers across the world. Combined with other daily sources of microplastics, we’re inhaling and ingesting these materials far more than ever before.

Roughly a decade ago, multiple countries banned exfoliating plastic “beads” from face scrubs, toothpaste, and hand cleaners to reduce microplastic waste. Meanwhile, scientists also started investigating potential health concerns of ingesting microplastics in full force.

Early red flags related to reproductive health. More evidence suggested microplastics are especially harmful to blood vessels. One study in 2024, for example, followed people with blood vessel disease due to a blockage. They analyzed the offending clumps and realized they were made up of tiny microplastic particles combined with broken down cells. Polluted by microplastics, the cells hung around inside the patients’ fatty tissues, spurring inflammation and increasing the chance of heart disease and stroke.

Even the brain was vulnerable to these toxins. Usually, our noggin is guarded by a cellular fortress dubbed the “blood-brain barrier.”  Only sanctioned chemicals and some larger proteins can pass through this barrier.

However, it didn’t evolve to block microplastics. Previous studies found these particles could drift into brain tissue, causing some proteins to clump up and trigger or worsen neurodegenerative diseases—conditions in which neurons break down—such as Parkinson’s disease. Microplastics have also been linked to anxiety and depression, though it’s still unknown why.

Scientists generally agree that microplastics floating across the blood-brain barrier can cause damage or spark inflammation in the body affecting neuron function, explained the team. But seeing is believing—which is where the new study comes in.

The Fast Lane

Rather than analyzing microplastic particles inside brain tissue, the team used a method called two-photon microscopy to track their journey inside a mouse’s brain. The method is particularly useful at visualizing changes inside the brain at high resolution.

They first laced the mice’s drinking water with a glow-in-the-dark version of a microplastic called polystyrene. The bubble-shaped material is prevalent in toys, appliances, and all sorts of packaging. Within two and a half hours, they noticed the particles flowing through blood vessels in the brain. Some particles looked like comets trailing tails, wrote the authors.

If, as previously suggested, microplastics flow into the brain unprotected, they would likely spread across the entire brain. Surprisingly, the particles eventually concentrated in cells.

After isolating the cells containing microplastics, the team realized they were the brain’s immune cells. These cellular warriors readily “eat up” invaders, such as bacteria or viruses. But microplastics gave them indigestion. After consuming the particles, the cells became bloated, turning into oblong-shapes that clustered inside blood vessels and blocked blood flow.

The shapes were just the right diameter to jam blood vessels in the brain—especially those connecting deeper brain regions to the cortex, a neural highway that controls movement, learning, and memory. In several tests, mice given a dose of microplastic struggled to run around a playground or grab onto a “monkey bar.” They also failed to remember places.

The good news? Most of these cognitive problems went away within a month. The team is still trying to figure out how the brain eventually cleaned out the microplastics, and whether the blockages—like blood clots—have lingering health problems.

To be clear, although the research adds to increasing evidence that microplastics could enter and potentially harm the brain, the results are only in mice. The conclusions will need to be verified in people, who have far larger blood vessels in the brain that could potentially thwart the negative effects of microplastics.

However, studying the impact of microplastics on the brain could inform how we manufacture the next generation of medical devices—for example, swapping out plastic casings for other biocompatible materials.

If those devices aren’t “rapidly and thoroughly improved,” then they could “become a persistent and potentially recurrent issue,” wrote the authors. “Increased investment in this area of research is urgent and essential to fully comprehend the health risks posed by [microplastics] in human blood.”