The human body is a well-functioning, complex system made up of trillions of cells. As you can imagine, our body must be compartmentalized – we have organs, made of specific tissues, which are composed of specific cells. They can be tightly connected, creating walls that separate one part of the body from another. However, substances must travel between these compartments. Nutrients or oxygen must squeeze through vessel walls to reach our organs. If that weren’t possible, what would be the point of having a heart tirelessly pumping blood?

Cell walls have different levels of permeability. In some places, a molecule can pass through easily, while in others, the same molecule cannot. This selective permeability helps keep everything organized and functioning properly. But what if, out of nowhere, a strange particle – an outsider – enters our system and squeezes through anything, disregarding the rules followed by everything else?

Ladies and gentlemen, that particle is plastic.

Plastic is everywhere. While the public is increasingly aware of the environmental pollution, many remain unaware of the full extent of the problem. We often see plastic bottles thrown away in parks, but there is an even greater, unseen threat – microplastics (defined as pieces smaller than or equal to 5 mm; Thompson et al., 2024).

In their review, Thompson and his team highlight that microplastics have been found in seawater, deep-sea sediments, sea ice, lakes, rivers, and even on the highest mountains. How does it get there? There are many ways in which plastic trash can be fragmented and transported – by human activity or by environmental processes. One less obvious source of microplastics is clothing. There is growing awareness about how much waste is produced by the fashion industry. Fast fashion is not only “fast” because trends change quickly, but also because of how rapidly it is killing our planet. Every tear, wash, and wear releases microplastic particles. Even doing laundry releases thousands of microfibers into the environment. To address this specific issue, in 2022, the University of Amsterdam established a research team called “Science in and with Society: Reducing Emissions of Textile Microplastics in the Netherlands (SISTEM-NL Overview | METAcitizenscience, n.d.).

We drink microplastics from our water and eat them with our food – without even realizing it. That’s how they enter our bodies. Of course, if you were to swallow a square centimeter of plastic, it would likely pass through your digestive system without ending up in your lungs or brain. However, the real harm comes from plastic debris – the aforementioned microplastics. Although our cells are tightly connected, microplastics can still find a way to squeeze through them, and the scariest part is that we do not fully understand their effects on our bodies.

A growing number of studies report the presence of microplastics in various organs. One of the most concerning findings involves their concentration in the placenta and amniotic fluid – environment that is supposed to be safe and nourishing for a developing fetus (Halfar et al., 2023; Xue et al., 2024). If plastic affects adult organisms, we can only imagine how much more detrimental its effects might be on a developing human.

The very barriers designed to protect our bodies can sometimes pose a problem. Our brain is one of the most vital organs – that is why it is so well-protected. To safeguard it, we have a skull – a rigid, bony box with only tiny entries for essentials. However, this protection can become an obstacle when something goes wrong in the brain, such as the development of a tumor. Even if we had the perfect medication, the likelihood of it reaching the brain from the bloodstream is low. This is due to the blood-brain barrier, the tightest layer of cells in our body (Dotiwala et al., 2023).

What is even more puzzling is that Nihart et al. (2025) found accumulation of microplastic in the brain of a deceased human. The research offers some insight into the topic, but the direct mechanism by which plastic can cross this barrier is not understood. That might be one silver lining – perhaps by understanding how microplastics enter the brain, we can find a new way to deliver medication more effectively.

All these studies can be terrifying. Microplastics are everywhere. But we do not need to panic. A lot of studies are being conducted, and we should not jump to conclusions too soon.

For example, a study performed by Xu et al. (2023) caused quite a stir, as it showed that plastic shedding from baby feeding bottles. However, a paper by Gerhard et al. (2022) showed that flows in methods used for microplastic detection can lead to false positives, which might have been the case in Xu’s study.

Microplastic is a new reality, and we are still trying to find the best way to study it. There are teams dedicating their time to creating new, reliable methods to study the fate of plastic in our environment and in our bodies. We know that it is there, but we are not sure what it is doing or how it is squeezing through our barriers.

What we do know is that we must limit plastic production, be aware of the issue, and give scientists the space and time to answer some of these burning questions. The upcoming years will bring more answers.