Everywhere you look, microplastic pollution is a growing crisis. Tiny plastic fragments have been found in oceans, food, drinks, and even human tissues. We’ve only learned about them recently, but they seem to be a real threat to our health. New research published in Science Advances reveals an alarming discovery: microplastics are making their way into your bloodstream, where they can obstruct blood vessels and cause neurological damage.

The study found that microplastics in the bloodstream of mice can penetrate the blood-brain barrier, blocking blood flow in the brain. This was found to lead to cognitive and motor impairment as well as dangerous blood clots.

Microplastics are everywhere

Microplastics — plastic particles less than 5 millimeters in size — come from a variety of sources. They originate from degraded plastic waste, industrial production, and even the synthetic fibers in our clothing. These particles have been found in human food, drinking water, and the air we breathe.

If you think it doesn’t affect you, you’re wrong. They’ve been found everywhere from the bottom of the ocean to Mount Everest, as well as inside humans. If you see plastic around you, there’s a good chance there’s plastic inside you. According to one study, you’re eating around one credit card’s worth of plastic every week.

Microplastics can enter the human bloodstream in different ways. Contaminated food and water can introduce them into the digestive system, allowing some particles to pass into circulation. Inhalation of airborne microplastics is another route, as the lungs can absorb these tiny particles.

Don’t panic just yet, because we don’t really know how much of an impact this has on our health. So, the new study, led by Haipeng Huang from the Research Academy of Environmental Sciences, Beijing, China, investigated just that.

Investigating microplastics in mice

Researchers introduced fluorescently labeled microplastics into mice using two methods: ingestion and direct injection. In the ingestion method, mice were given water containing microplastics allowing the particles to pass through the digestive system and enter the bloodstream. In the injection method, the plastics were introduced directly into the bloodstream via intravenous injection, mimicking potential medical exposure.

This approach, where the plastics were labeled and detectable, enabled scientists to track the movement of microplastics in real-time, observe their interactions with immune cells, and analyze their impact on blood flow and brain function.

“We first observed MPs moving within the bloodstream 2 hours and 20 min after treating mice . The movement of the MP resembled a lightning bolt in a dark vascular region,” the researchers write in the study.

After the microplastics started moving, a part of them was absorbed by immune cells. This turns the cells into what the researchers call “MPL-Cells” (Microplastic-Loaded Cells). These cells become significantly larger after consuming MPs, making them more likely to get stuck in small blood vessels, obstructing blood flow just like a clot.

Microplastics cause mice a lot of problems

In live imaging, researchers observed that MPL-Cells often became lodged in the narrow capillaries of the brain. Some MPL-Cells remained stuck in brain blood vessels for over a week. While some of these cells eventually moved on, others remained permanently trapped, which could cause chronic damage.

The study didn’t just stop at observing microplastic blockages; researchers also examined the effects on brain function. Mice exposed to microplastics showed significant cognitive and motor impairments. They moved less and performed poorly in motor tests, suggesting impaired brain function. They also struggled in tasks requiring balance and coordination, such as the rotarod test.

While this is not confirmed, these behavioral changes suggest that prolonged exposure to microplastics may contribute to neurodegenerative diseases. If this effect translates to humans, MPs could be a hidden risk factor for stroke, dementia, and other neurological disorders.

Not all microplastics are equally bad

The study found that larger microplastics (5 microns in diameter) were more likely to cause blood vessel obstruction than smaller ones. This suggests that they wouldn’t be as harmful to humans (simply because we have larger blood vessels than mice), but it doesn’t rule out the risk at all.

Larger particles were also more likely to be phagocytosed by immune cells, leading to bigger obstructions, and they also tended to stay in place for a longer time. This suggests that regulating the release of larger microplastics into the environment—such as those from industrial processes and synthetic textiles—could reduce their impact on human health.

More research is needed to determine the exact level of risk to humans but microplastics don’t seem to be benign guests inside our bodies.

The study was published in Science Advances.