There’s a Sandwich Bag of Plastic in Your Brain

This transcript has been edited for clarity. 

Welcome to Impact Factor, your weekly dose of commentary on a new medical study. I’m Dr F. Perry Wilson from the Yale School of Medicine.

We are what we eat, and what we drink. And increasingly we are eating and drinking plastic.

Plastic is all around us. It’s in our water bottles and shopping bags, our tubes of toothpaste and shampoo, the containers that hold our food, our cups and plates and knives and forks. I sometimes think of how we look back with a certain superiority on Roman elites with their penchant for lead cutlery — little did they know that their very forks and spoons were killing them. And then I wonder if people in the future will look back at us with a similar feeling: Our poor ancestors. How did they not realize that eating things that don’t biodegrade was bad for them? 

Microplastics and nanoplastics — tiny bits of plastic as small as 1 nanometer across — have been found in a variety of human tissues: lungs, placenta, and lipid-rich plaques in the carotid arteries. I think we all feel a sense of unease when we hear that; these things are clearly not supposed to be there. But to be fair, we don’t yet have clear evidence that they are directly harmful, though there are some suggestive data coming out of animal studies.

But the unease I have knowing that my lungs or liver or kidneys might have microplastics lodged in them is nothing compared with the unease I felt reading a study that measured nano- and microplastics in the brain — and found more there than anywhere else. A lot more.

It’s always good practice to make a hypothesis before you read actual study data so you can ground yourself in your own expectations and biases. So when I saw this study, appearing in Nature Medicine, from Matthew Campen at the University of New Mexico and colleagues, examining tissue concentrations of nano- and microplastics in the liver, kidney, and brain, I made my predictions.

Maybe this is the nephrologist in me talking, but I assumed we would see the highest levels of these things in the liver and kidneys, the organs that are supposed to filter stuff out of our blood. The brain should be relatively protected, right? We have a blood-brain barrier which is there to make sure things like this don’t get into that precious cerebral environment. But this study shows just the opposite of what I expected. And that is chilling.

Let’s go through how it was done. This was an autopsy study. Tissue samples were collected from biobanks around the country, and most of the analyses I’ll show you involved something like 30 decedents.

One of the innovations of this study was the ability to measure nanoplastics. Many of the prior studies assessed the presence of microplastics using light microscopy. You can see some microplastics lighting up under polarized light in this microscope image of the liver.

But nanoplastics are simply too small to be seen with a standard microscope. Here’s a picture of brain tissue using the same polarized light microscope; you see one tiny bit of plastic (circled). Not too bad. But light microscopy is misleading here.

The researchers complemented traditional light microscopy with gas-chromatography mass-spectroscopy to identify particles that are way too small to see under a conventional microscope. This is really the key to understanding what’s going on in the brain. That blood-brain barrier does work; it keeps larger pieces of plastic out. But the very small pieces make it through and, it seems, get stuck there. 

Let’s look at some of the results.

This graph shows the concentration of nano- and microplastics across the three organs of interest at two time points: individuals who died in a period around 2016, and then a group who died more recently, around 2024. Clearly, you can see that brain is highest here. But were you paying attention to the Y-axis? This is on the log scale.

If I transform the data to a simpler linear scale, you can see that the brain concentration is not just higher; it is dramatically higher. 

Let me put these numbers in some context. The concentration measured in the brain was about 4000 micrograms per gram of brain tissue. The frontal cortex of the brain (where these samples were taken) weighs around 500 grams. So, assuming the samples are representative, we’re talking 2000 milligrams of plastic in the frontal cortex. Two grams. That’s like a plastic sandwich bag in your brain. It’s really disturbing.

The other disturbing finding: The levels increased from 2016 to 2024. In fact, in a remarkable bit of unintentional health equity, there were no differences in plastic concentrations between men and women, between people of different races, or even by age. The only factor significantly correlated with how much plastic was in your brain was the year you died. More recently? More plastic.

The researchers were able to measure not only how much plastic was in there but exactly what kind of plastic it was. This is crucial if we are going to try to figure out what the source is. By and large, across all the tissues, the plastic was polyethylene, shown here in orange.

This is not particularly surprising. Polyethylene is the most commonly produced plastic. It doesn’t biodegrade, and it is the main component of a ton of stuff we use every day, including our good friend the sandwich bag. But you also find polyethylene in water bottles, plastic films, and storage containers. It’s everywhere. It’s almost unavoidable.

A subset of the individuals studied had dementia at the time of death. Plastic levels were even higher in the brains of that group — on the order of 20,000-50,000 micrograms per gram, or around 10 sandwich bags on our helpful scale. 

This obviously leads to a correlation vs causation question. Does accumulation of microplastics in the brain cause dementia, or are people with dementia more susceptible to accumulation of microplastics in the brain? It may well be the latter, due to weakening of the blood-brain barrier in dementia states. Future studies will tell, I suppose.

In the meantime, I’m not taking any chances. This particular study could not measure the source of polyethylene among the individuals. But other studies have looked at where we get most of our exposure from. The truth is, these substances are everywhere. They are in the food we eat, the water we drink, the air we breathe, the clothes we wear. That said, there are some easy targets here. 

First on the list: plastic water bottles. The bottles themselves (especially the caps) are significant sources of microplastics in general and polyethylene in particular. A study in Environmental Science & Technology estimated that those who drink most of their water via plastic bottles ingest an extra 90,000 particles of microplastics a year, compared with 4000 for those who consume only tap water. It’s an easy fix to bring a reusable glass or metal bottle with you. Takeout containers are probably a problem as well, particularly if you reheat the food in the microwave, so maybe transfer food to a plate before you nuke it. The other major source of polyethylene exposure is from the air we breathe: fibers from carpets and other textiles, dust from plastic goods, and so on. This study found that perhaps half of our microplastic ingestion happens just from breathing. 

The truth is, there’s really no way to avoid this stuff entirely — not in modern society. If we really want to reduce our exposure, larger steps at the national and international level to limit the use of plastics in manufacturing will be necessary. It might be a reasonable idea, if we have the brains for it. 

F. Perry Wilson, MD, MSCE, is an associate professor of medicine and public health and director of Yale’s Clinical and Translational Research Accelerator. His science communication work can be found in the Huffington Post, on NPR, and here on Medscape. He posts at @fperrywilsonand his book, How Medicine Works and When It Doesn’t, is available now.