Where Do Microplastics Actually Go Once They're Inside You?

This article explains where microplastics go after entering your body, which organs they accumulate in, and what scientists currently know about how your body handles them.

There's a jar of tomato sauce in my fridge that I've been avoiding. Not because it's expired. Because I noticed something the last time I opened it - a faint plastic smell, barely perceptible, like the ghost of the container it came in. I'm probably imagining it. Or maybe not. That's the thing about microplastics - once you start noticing, you can't really stop.

Where Microplastics Accumulate in the Human Body - Key Findings

Organ/Tissue	Detection Rate	Primary Plastic Types Found	Key Research Findings
Brain Tissue	100% of samples	Polyethylene, PVC, Polystyrene	0.5%–5% of dry brain weight; tenfold increase from 2016 to 2024; particles cross blood-brain barrier
Blood	Widely detected	Various polymer types	Nanoplastics small enough to circulate throughout entire body; can theoretically cross any membrane
Liver	56% of samples	PET (water bottles), Polypropylene	Particles cluster near blood vessels and bile ducts; suggests selective retention, not random distribution
Kidneys	62% of samples	Multiple polymer types	Concentrated in specific zones; filtration system unable to clear particles effectively
Lungs	Confirmed present	Inhaled microplastic fibers	High blood flow increases accumulation; particles from air pollution and synthetic textiles
Placenta	Detected in samples	Various polymers	Particles can transfer from mother to developing fetus; found in placental tissue
Breast Milk	Confirmed present	Various polymers	Direct transfer pathway to nursing infants; long-term implications unknown
Digestive Tract/Stool	Present in all samples tested	Food-contact plastics, packaging materials	Some particles pass through and are excreted; percentage that remains vs. exits is unknown

The question that keeps coming up isn't just "how much plastic are we consuming?" We covered that in the first piece. The real question - the one that makes research teams nervous when you corner them at conferences - is: where does it all go?

Because here's what we know for certain: microplastics are in us. In blood, lungs, liver, kidneys, placenta, breast milk. They've been found in human stool, which tells us at least some passes through. But what about the rest? What about the nanoplastics - particles so small they can theoretically cross any membrane in your body?

The answer is messier than anyone wants to admit.

The Blood-Brain Barrier Isn't What We Thought

Let's start with something most people think is impenetrable: the blood-brain barrier. It's a selective membrane system that wraps around your brain's blood vessels, filtering what gets through. It keeps out most large molecules, toxins, bacteria. It's one of the reasons the brain is so hard to treat pharmacologically - getting drugs across that barrier is notoriously difficult.

But nanoplastics, it turns out, are small enough to slip through.

A 2024 study in Environmental Science & Technology detected microplastics and nanoplastics in human brain tissue for the first time. They looked at samples from 51 individuals collected between 2016 and 2024, and found plastic particles in every single sample. Not some. All.

The particles were predominantly polyethylene - the plastic used in bags and bottles - followed by polyvinyl chloride (PVC) and polystyrene. The concentrations ranged from 0.5% of the brain's dry weight on the low end to nearly 5% on the high end. Five percent. That's not trace contamination. That's structural.

What's worse - and this is where it gets genuinely concerning - they found a temporal trend. The samples collected in 2016 contained about 0.5% plastic by weight. By 2024, that had jumped to around 4.5%. Almost a tenfold increase in eight years.

I don't know what to make of that. Neither do the researchers, really. They're careful not to speculate too aggressively. But it suggests accumulation. It suggests these particles aren't just passing through. They're staying.

Accumulation vs. Clearance

Your body has clearance mechanisms for almost everything. Kidneys filter blood. The liver processes toxins. The lymphatic system drains waste. Even the brain has its own waste-clearance system - the glymphatic system, which flushes out metabolic debris while you sleep.

But plastic particles don't behave like typical toxins. They're not water-soluble. They don't break down chemically in any meaningful timeframe. Some animal studies suggest they can accumulate in tissues indefinitely, especially in organs with high blood flow - liver, kidneys, lungs. Others suggest at least partial excretion through stool.

The truth is probably somewhere in the middle, but we genuinely don't know the ratios. How much stays? How much leaves? Does it depend on particle size? Polymer type? Individual physiology?

A 2023 paper in Science of the Total Environment found microplastics in human liver samples - 56% of the samples contained particles, primarily polyethylene terephthalate (PET, the plastic in water bottles) and polypropylene. The particles were clustered in specific zones, particularly near blood vessels and bile ducts. That's not random distribution. That's selective retention.

Another study from the same year detected microplastics in human kidneys - 62% of samples. Again, not evenly distributed. Concentrated in certain areas. The researchers couldn't say whether the particles were causing damage or just accumulating passively, but they noted inflammatory markers were elevated in some samples.

I keep thinking about that word: passive. As if accumulation without immediate harm is somehow reassuring. But accumulation itself is the harm, isn't it? Even if there's no acute toxicity, even if the cells aren't dying en masse, you're still building up a material that doesn't belong there. A material your body has no evolutionary mechanism to process.

The Placenta Problem

Here's where it gets harder to stay neutral.

A 2020 study published in Environment International found microplastics in human placenta for the first time. Six placentas from healthy pregnancies, all collected in Italy, all contaminated. Twelve particles in total - polypropylene mostly, with some polyethylene. The particles were found on both the maternal and fetal sides, as well as in the amniochorionic membranes.

The fetal side. That's the part that matters. That means particles crossed from maternal circulation into the placenta itself, and potentially into the fetus.

A follow-up study in 2024, also in Environment International, looked at 62 human placentas. Every single one contained microplastics. The median concentration was around 200 micrograms per gram of tissue - not massive, but consistent. The most common polymer was polyethylene, followed by PVC and polystyrene.

They also found a correlation with pregnancy complications. Placentas from pregnancies with preeclampsia - a serious condition involving high blood pressure and organ damage - had significantly higher microplastic concentrations than uncomplicated pregnancies. That's not proof of causation. It could be reverse causation. It could be confounding. But it's enough to make you pause.

I don't have kids. But if I did, that study would keep me up at night. Not because I'd know what to do about it - there's not much you can do, really, short of living in a bubble. But because it shifts the frame from "personal health risk" to "intergenerational exposure." You're not just dealing with your own body anymore. You're dealing with biology that hasn't even formed yet.

What About Lung Tissue?

We inhale microplastics constantly. They're in indoor air, outdoor air, dust, clothing fibers, car interiors. A 2022 study in Science of the Total Environment estimated that people inhale between 272 and 307 microplastic particles per day just from breathing. That's separate from ingestion.

Where do those particles go? Some get trapped in mucus and coughed up. Some get swallowed and end up in the digestive tract. But some - the smallest ones, the nanoplastics - make it deep into the lungs, into the alveoli, where gas exchange happens.

A 2022 paper in Science of the Total Environment (different one) found microplastics in human lung tissue. They examined samples from 13 patients undergoing surgery for lung cancer - not ideal, because cancer complicates interpretation - and found particles in 11 of them. Polypropylene and PET, mostly. The particles were embedded in the lung parenchyma - the actual tissue, not just sitting on the surface.

The concerning part isn't just that they're there. It's that lung tissue is supposed to be sterile. It's supposed to be protected by the respiratory epithelium, by mucus, by immune cells. But microplastics bypass all of that. They're inert enough not to trigger acute immune responses, but foreign enough to stay.

Some researchers think chronic low-level inflammation might be the real issue. Not immediate toxicity, but persistent irritation. The kind of thing that doesn't show up for years, maybe decades. The kind of thing epidemiology will struggle to link definitively because the exposure is so ubiquitous there's no clean control group.

The Gut-Microbiome Angle

I almost forgot to mention the gut. Actually, that's not true - I didn't forget, I just wasn't sure how to frame it without sounding alarmist. Because the data here is genuinely unsettling, but also incomplete.

Your gut microbiome - the trillions of bacteria, fungi, viruses living in your intestines - is fundamental to digestion, immunity, even mental health. It's sensitive to environmental shifts. Antibiotics disrupt it. Diet alters it. Stress affects it.

A 2024 study in Environmental Science & Technology found that microplastics can alter gut microbiome composition in mice. Specifically, they reduced microbial diversity and increased the abundance of potentially pathogenic bacteria. The mice also showed increased intestinal permeability - "leaky gut," if you want the colloquial term - which allows larger molecules to pass from the gut into the bloodstream.

That's mice, not humans. But the mechanisms are likely similar. Microplastics physically disrupt the gut lining. They provide surfaces for bacteria to colonize, potentially altering which species thrive. Some particles even carry absorbed toxins - phthalates, flame retardants, heavy metals - which leach out once they're in the gut.

Human studies are just starting. A 2023 paper in Environmental Health Perspectives found that people with inflammatory bowel disease (IBD) had higher fecal microplastic concentrations than healthy controls. Again, that's not proof of causation. But it's another correlation that makes you wonder.

So What Actually Happens Long-Term?

Honestly? We don't know. The human studies are mostly cross-sectional - snapshots, not timelines. We know microplastics are in tissues. We know they accumulate. We know they correlate with certain conditions. But we don't have longitudinal data showing how exposure over decades affects health outcomes.

Part of the problem is that controlled studies are nearly impossible. You can't ethically expose one group of people to high levels of microplastics and compare them to a control group decades later. And you can't find a true control group anyway, because everyone is exposed.

What we do know from animal studies is concerning enough. Microplastics cause oxidative stress - an imbalance between free radicals and antioxidants that damages cells. They trigger inflammation. They disrupt endocrine signaling. In some studies, they've been linked to reproductive toxicity, liver damage, neurodevelopmental effects.

But animals aren't humans. Dose-response relationships differ. Metabolism differs. Lifespan differs. Extrapolating is tricky.

The most honest answer I can give is this: we're running an uncontrolled experiment on ourselves. The exposure is universal. The timeline is decades. The endpoints are unknown.

Some days that feels manageable. Other days it feels like something we should've seen coming.