What Plastics Are Actually in Your Body? The Polymer Breakdown

We know microplastics are in human bodies. The harder question is which plastics — and whether the ones we hunt for in food are even the ones showing up in people. A 2024 systematic review set out to answer exactly that, analysing polymer type, shape, and size across 396 publications spanning seafood, fish, drinking water, meat, plant-based food, and human tissue samples.[IJMS, 2024]

The answer reframes a lot of the conversation. The plastic humans are most exposed to is not the water-bottle plastic most people picture. It is polyester — the stuff of clothing, carpets, and upholstery — and it arrives mostly in the form of fibres.[IJMS, 2024]

This matters because almost all microplastic toxicology research has been testing the wrong material. Understanding what is actually in us is the first step to studying whether it harms us.

Polyester leads, and it is not close

Across human samples, the review found that five polymers account for nearly 90% of the microplastics detected: polyester (PES) at 38.8%, polyamide (PA) at 17.1%, polyurethane (PU) at 15.3%, polypropylene (PP) at 9.4%, and polyacrylate (PAC) at 8.0%.[IJMS, 2024]

38.8%

Polyester’s dominance tracks with how much of it we make and how we use it. The review notes its enormous global production and its ubiquity in food packaging, clothing, and home textiles like rugs, mattresses, and furniture. It also appears across food sources — 26.4% of the plastics in aquatic food and 23.7% in drinking water — suggesting widespread contamination of water resources, not just packaging transfer.[IJMS, 2024]

Polyamide, better known as nylon, is the second most common in people despite having one of the lowest production volumes of the polymers studied. The review links this to environmental sources such as the release of microplastics from nylon fishing nets, alongside contamination during food processing.[IJMS, 2024]

Why polyurethane is a puzzle

Polyurethane is the third most common polymer in human samples, yet it barely registers in food. In aquatic food and drinking water it accounts for 0.5% or less, and it has not yet been recorded in meat or plant-based food at all.[IJMS, 2024]

So how is it getting into people? The review points to where it was found — vascular tissues, placenta, maternal fluid, and the meconium of infants — and cites work suggesting the contamination of pregnant women and infants with polyurethane comes primarily from indoor dust, given its heavy use in furniture, carpets, and clothing.[IJMS, 2024]

Fibres are the signature of the textile industry

If one finding deserves attention, it is shape. Fibres are the most prevalent form of microplastic in human samples, at 44.5%, and they dominate across food sources too: seafood invertebrates (59%), fish (68.8%), meat (45.4%), and plant-based foods (49.2%), and they are the second most common shape in drinking water.[IJMS, 2024]

That pattern lines up with the polymer data. Polyester, nylon, and polyurethane — the three leading polymers in human samples — are all common textile materials. The review reads the combination as a clear signal of environmental contamination from the textile industry.[IJMS, 2024]

44.5%

The scale of fibre shedding is striking. The review cites an estimate that a single 6 kg domestic wash load of acrylic fabric could release over 700,000 fibres, with polyester nearing 500,000.[IJMS, 2024] And while drinking water treatment plants often remove more than 95% of microplastics, the review notes that the pervasive fibre contamination of every food source suggests current measures still fall short of preventing human exposure.[IJMS, 2024]

The measurement problem: we may be looking at the wrong particles

Here is where the review turns genuinely uncomfortable. The particles we count depend entirely on the particles we are equipped to see — and different fields are looking at completely different size ranges.

In fish samples, 86% of studies analysed microplastics larger than 10 micrometres, and 44% looked only at particles above 100 micrometres. But in human samples, 59% of studies set their detection limit below 10 micrometres, and none went above 100 micrometres.[IJMS, 2024] In other words, seafood research tends to catch big particles; human research tends to catch small ones. Any direct comparison between them is partly comparing instruments, not realities.

The size of the detection window also changes the headline numbers enormously:

Smallest size detected	Studies	Avg. particles per study
≤1 µm	38	3,031
1–10 µm	63	937
10–100 µm	147	726
>100 µm	84	211

When researchers look down to 1 micrometre or smaller, they record roughly fourteen times more particles per study than those stopping above 100 micrometres.[IJMS, 2024] The review notes one 2024 study that measured bottled water down to the nanometre scale and estimated around 2.4 × 10⁵ particles per litre — an order of magnitude higher than earlier reports — suggesting that roughly 90% of plastic particles go uncounted by lower-resolution methods.[IJMS, 2024]

The honest limits of the data

A credible read of this review has to include what it cannot yet say. The authors flag several gaps directly.

First, the evidence base is lopsided. Research on microplastics in meat (8 studies) and plant-based food (5 studies) is still emerging and thinly represented, so conclusions there warrant particular caution.[IJMS, 2024]

Second, shape identification often relies on visual assessment, which introduces bias. The review highlights that the “film” shape ranked second in human samples largely because of a single study reporting 8,529 particles — a dataset large enough to skew the overall picture, and one the authors say needs confirmation.[IJMS, 2024]

Third, and most consequential for health research: toxicology has been testing the wrong plastic. More than 82% of toxicity studies focus on polystyrene, yet polystyrene is just 2.2% of what is actually found in people.[IJMS, 2024] Most of those studies also use spherical particles, while the real-world dominant shape is the fibre — a form with a very different surface-to-volume ratio and, likely, different biological behaviour.[IJMS, 2024]

The review does not claim to establish that any of these particles cause disease. It explicitly avoids ranking exposure by concentration precisely to reduce the distortion from inconsistent methods, and it calls for standardised protocols and more work on particles below 10 micrometres.[IJMS, 2024]

What to actually take from this

For now, the practical signal is about sources, not panic. The polymers most present in human samples — polyester, nylon, polyurethane — are textile materials, and fibres are the dominant shape. That points as much to clothing, soft furnishings, and indoor dust as it does to anything you eat or drink.[IJMS, 2024]

It also sets a clear direction for the science. Future toxicology should shift away from spherical polystyrene toward the materials and shapes people are genuinely exposed to, and the field needs shared methods before any exposure number can be trusted as more than an estimate.[IJMS, 2024] Until those methods exist, treat every tidy statistic about microplastics — including the ones here — as a best current reading rather than a settled fact.