Microplastics Have Been Linked With Myriad Human Health Problems. Scientists May Have Finally Figured Out How They Harm the Body

Lab experiments suggest that tiny bits of plastic can react with water inside us to produce highly reactive molecules. They can lead to damaging oxidative stress and inflammation

Sara Hashemi | Daily Correspondent

October 16, 2026 1:03 p.m.

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Microplastics have been found throughout the human body, including the brain, lungs and blood. Past studies have identified associations between the tiny particles and various health issues, such as cardiovascular disease, dementia and reproductive problems. But the exact way they might contribute to these problems has been unclear.

Now, scientists say they’ve found an answer: Microplastics appear to generate highly reactive molecules when they interact with water. If the same effect were to happen in our bodies, microplastics could lead to oxidative stress, which damages cells, and inflammation. The findings, published in the journal Nature on October 14, challenge the idea that plastics don’t easily react with other substances and point to how they can cause harm to humans.

“We’ve long assumed that plastic itself is inert, and that any harm from microplastics comes from the chemicals added to plastics or the pollutants that stick to them,” Lisa Patel, a physician at Stanford Medicine Children’s Health who wasn’t involved in the study, tells Everyday Health’s Becky Upham. “This study suggests the surface of the plastic particle can be chemically active on its own.”

Bulk plastics are generally thought of as durable and chemically resistant, but that “needs to be reconciled with the toxicity of their fragmented microscale forms,” the authors write in the study. When plastics degrade into microplastics—pieces smaller than a pencil-tip eraser—their surface-to-volume ratio goes up. For example, if a credit card gets broken down into bits just ten microns in diameter, or around one-tenth the thickness of a sheet of paper, that increases its surface area more than 200 times, explains study co-author Wei Min, a chemist at Columbia University, to Payal Dhar at Scientific American. The more exposed area, the more chemical activity.

To better understand how these tiny fragments might generate chemical activity, Min and colleagues examined particles of widely used bulk plastics, including polyethylene, polypropylene, polystyrene, polyvinyl chloride and polyethylene terephthalate.

Analyses revealed that when microplastics interact with water, they spontaneously generate unstable molecules known as reactive oxygen species. Because plastic repels water, or is hydrophobic, the surrounding water can’t form its usual hydrogen bonds. So, contact between the two substances results in electric changes that can help create volatile molecules called hydroxyl radicals.

Microplastics are therefore “like a permanent little factory” that generates this reactive oxygen species, Min tells Evan Bush at NBC News. “Our cells are 60 to 70 percent water, and therefore this effect could be ubiquitous.”

These harmful hydroxyl radicals were even produced when the team mixed microplastics with mouse blood, although the effect was smaller than in water. In response, some red blood cells seemed to change shape, and their activity levels shifted. “We do show immediate biological consequences,” Min tells NBC News. “Proteins get damaged. Cells get damaged.”

However, the exact size and mechanism of this effect is still unclear, and it may depend on how our bodies get rid of microplastics, Min tells Jo Marchant at New Scientist. “How much plastic is in a regular human being? We have no idea right now.”

What’s more, adding a chemical called a surfactant that weakens the forces holding water molecules together reduces the generation of hydroxyl radicals, the team found. And some substances in the body, such as certain lipids, have this property.  

“Microplastics hit your lung, and they are surrounded by surfactants immediately,” Matthew Campen, a biochemist at the University of New Mexico who wasn’t involved in the study, tells New Scientist. “In most situations that I can imagine in a biological system, they will be surrounded by those lipids. The big concern is [whether] this is getting worse over time, and we really need to get a handle on what the health effects are, or could be, so that we can avoid exposures.”

Still, the findings give scientists a new way to look at plastic pollution’s impacts, says Martin Wagner, a toxicologist and a biologist at the Norwegian University of Science and Technology who wasn’t involved in the work, to Scientific American. “It implies microplastics themselves are a source of oxidative species ... and oxidative stress is not a secondary effect of exposure.”

Sara Hashemi is a science writer and fact-checker currently based in New York City. Her work has appeared in Sierra, The Body, Maisonneuve magazine and more.