Microplastics are inside you right now. Here's what that actually means.

They’ve been found in human blood, brains, testes, placentas, breast milk and lungs. The question is no longer whether you have them. It’s what they’re doing in there.

Researchers in Amsterdam found a measurable amount of plastic particles in the blood of 17 of 22 healthy volunteers (77%). An Italian team found microplastic fragments in 4 of the 6 human placentas they examined. They’ve turned up in 23 of 59 breast milk samples in a Thai study, in every human and dog testis tested in a New Mexico study, in 11 of 13 samples of human lung tissue, and, in a 2025 study in Nature Medicine, in human brain tissue at concentrations higher than in the liver or kidneys.

You have plastic in your body. So do we. So does basically everyone reading this (there are dozens of us!).

The question isn’t “are you sure about that?” anymore. It’s “okay, so how does that affect me?” That’s harder, and we’re going to answer it honestly, including the parts where the science is still catching up.

What we’re actually talking about

Plastic doesn’t biodegrade. Sunlight, waves and wear break it into smaller and smaller pieces. Pieces under 5 millimeters are microplastics. Pieces under 1 micrometer are nanoplastics. The particles that the 2025 brain study isolated were mostly nanoscale, shard-like fragments, which is part of why researchers are so focused on the small stuff.

The contamination is global, and we mean that literally. Microplastics have been found in cloud water at the summits of Japanese mountains, including Mount Fuji, in sediments of the Mariana Trench, in Antarctic sea ice, and in the exhaled breath of wild bottlenose dolphins. This isn’t a local pollution problem you can move away from.

What the brain study found, and what critics say

The brain study deserves a closer look, because it gets cited a lot (including by us).

The University of New Mexico team analyzed liver, kidney and brain tissue from people who died in 2016 and in 2024. They report that brain samples had substantially higher concentrations than liver or kidney, 7 to 30 times higher, and that concentrations in liver and brain were higher in 2024 than in 2016. Brain samples from 12 people with a dementia diagnosis had even more. The authors are clear that this doesn’t show plastic causes dementia: dementia itself damages the blood-brain barrier and the brain’s clearance systems, so “no causality is assumed.”

There’s a bigger caveat. The method used here, pyrolysis gas chromatography-mass spectrometry, burns a sample and measures the breakdown products. Fats can produce signals that look like polyethylene, and the authors themselves flag lipids as a potential source of interference, which matters a lot for an organ as fat-rich as the brain. In late 2025, a group of analytical chemists published a formal critique in the same journal arguing that the study had limited contamination controls and lacked validation steps, which may affect the reliability of the reported concentrations. Treat the exact numbers as unsettled. The finding that plastic reaches human organs is consistent across many labs and methods; how much, and where it concentrates, is still being worked out.

What it might be doing to your body

The science is solid on presence and still developing on harm. We know the particles are there. We know much less about what they cause, because studying long-term, low-dose exposure in humans is slow and hard. What we do know is not reassuring.

Microplastics aren’t just inert specks. Plastics carry chemical additives, including plasticizers like phthalates and bisphenols, and flame retardants, that can leach out and interfere with hormones. The research on these chemicals is considerably more developed than the research on the particles themselves.

In lab and animal studies, micro- and nanoplastic exposure has been linked to oxidative stress, inflammation and cell damage, and in mice fed food chopped on plastic cutting boards, to gut inflammation, a weakened intestinal barrier and shifts in gut bacteria. Animal results don’t automatically carry over to people.

On fertility: the New Mexico testis study found plastic in all 23 human and 47 dog testes it tested, with higher average levels in the human samples. But sperm counts were only measured in the dogs, where some polymers (polycarbonate and ABS) correlated with lower counts. We don’t have equivalent human data from that study.

The strongest human health signal so far comes from the heart. A 2024 study in the New England Journal of Medicine followed 257 people who’d had plaque removed from a neck artery. Polyethylene was detected in the plaque of 58% of them. Over about 34 months, those patients had a 4.5 times higher risk of heart attack, stroke or death from any cause than patients whose plaque showed no detectable plastic (hazard ratio 4.53). That’s an association in an observational study, not proof that plastic caused those events. It’s also exactly the kind of result that should have every health agency funding follow-up studies.

What we don’t know yet

You deserve to know the limits of the science, not just the scary parts. Researchers are still working out:

• What dose causes harm in humans. Most toxicity studies are in cells or animals.
• Whether, and how fast, the body clears these particles.
• Whether some plastic types are worse than others.
• Whether the particles or the chemicals they carry do most of the damage.
• How reliable current measurements in human tissue are (see above).

What we can say: every year, studies find plastic in more places in the body, and the health associations being reported point in a worrying direction. “We don’t know yet” is not the same as “it’s fine.”

So what do you do with this information?

You don’t panic. Panic is useful for exactly zero things. You cut your exposure where it’s easy and where it counts, and you push for the policy changes that address this at the source.

The kitchen is a good place to start: heating food in plastic, plastic cutting boards and plastic kettles are among the better-studied sources of particles in food. We’ve put together a kitchen swap guide ranked by exposure.

Individual action without systemic change is like bailing out a boat with one hand. But many hands matter, especially when they come with a vote, a dollar and a voice.