"Not proven harmful" is not the same as "harmless"
The first rule of toxicology – as old as Paracelsus in the 1500s – is that the dose makes the poison. A substance can be detectable without being harmful in the amount you are actually exposed to. That is why scientists carefully separate two things:
- Hazard: can the substance cause harm in principle?
- Risk: how likely is harm at the dose you actually take in?
The relationship is usually summed up in a simple principle:
Keep that distinction in mind throughout the article. A risk that has not been established is not a risk of zero – it means nobody yet knows how big it is. And when something is already in our organs and increasing over time, it is wiser to play it safe than to wait for final proof that may take decades.
Where in the body have microplastics been found?
The short answer: almost everywhere anyone has looked. Studies in recent years have detected micro- and nanoplastics in human blood, placentas, lungs, gut, liver, kidneys – and brain. This is new research: the first findings of plastic in blood are only a few years old.
The most widely discussed is a study in Nature Medicine (2025) that measured plastic in the organs of deceased people. The findings were striking in three ways:
- The highest levels were in the brain – several times more than in the liver and kidneys.
- The particles were extremely small – many were shards of just 100–200 nanometres (a nanometre is a millionth of a millimetre).
- Levels were higher in samples from 2024 than from 2016, suggesting that plastic builds up in the body – and in the environment – over time.
The fact that particles reach all the way into the brain tells us something important chemically: the very smallest pieces are small enough to pass barriers that normally keep larger things out. Size decides where a particle can go – and it is the smallest fraction that matters most.
But – and it's an important but: finding plastic in an organ tells us that particles get there. It does not yet tell us how much they do once they are there. That is the step from "hazard" to "risk" in the figure above, and it is the step research is still struggling with.
The strongest warning signal so far: the heart and blood vessels
If one single study moved the question from "unpleasant thought" to "we need to take this seriously", it is this one. In 2024 an Italian research team published a study in the New England Journal of Medicine – one of the most respected medical journals in the world – of 304 patients having surgery for narrowing of the carotid artery.
They looked for micro- and nanoplastics in the plaque that was removed (the fat and connective tissue that builds up in the artery wall). The result:
- In patients whose plaque contained plastic, the risk of a subsequent heart attack, stroke or death was about 4.5 times higher over the following ~34 months, compared with those in whom no plastic was found.
- The same group also had higher levels of inflammatory markers in the artery wall.
Chemically, the pieces fit together: a foreign particle embedded in an artery wall can keep up low-grade inflammation, and inflammation is one of the main drivers that make atherosclerosis worse.
Read it honestly: the study shows a link (an association), not a proven cause. The patients were already ill enough to need surgery, it is a single study, and we can't rule out that the plastic is a marker of something else (such as a less healthy lifestyle) rather than the cause itself. The researchers are clear about this themselves. But as an early warning flag it is hard to wave away – and it has made the whole field look more closely.
What plastic does in the lab – and why size is everything
When scientists expose cells and lab animals to micro- and nanoplastics, they repeatedly see a few effects, summarised in several review articles from 2025:
- Oxidative stress – the particles boost reactive oxygen species that wear down the cell's building blocks.
- Inflammation – the immune system reacts to the foreign material.
- Disrupted cell function – the smallest particles can get inside cells and disturb, for example, the mitochondria (the cell's power plants).
And here the main point comes back: the effects depend on size and dose. Nanoplastics (the smallest pieces) are consistently the most active, because they are small enough to pass through cell membranes. Microplastics (the larger pieces) are mostly swallowed and pass straight through.
The trap in lab data: to see a clear effect, lab studies often use very high doses and a single, pure type of plastic – far from the mix and the amounts a person meets in everyday life. That shows plastic can harm cells (the hazard is real). It does not automatically translate into "your everyday exposure harms you this much" (the risk is not established). Hazard ≠ risk.
The credit card myth: no, you don't eat a bank card a week
You have probably seen the figure: "we eat a credit card's worth of plastic – 5 grams – every week". It is gripping, it is shareable … and it is greatly exaggerated.
The claim comes from a 2019 WWF report, where 5 grams a week was the absolute upper end of a very wide range (0.1–5 grams), pieced together from many small studies with different measuring methods. The figure was also mixed up with a completely different study on inhaled plastic. When that study's own lead author redid the maths, he concluded it would take several thousand years to breathe in the weight of a credit card – not a week. Other recalculations land on an amount closer to a grain of salt, not a bank card.
Why bring this up when we sell plastic-free products? Because honesty is the whole point. You do eat and breathe in microplastics – that is true and worth taking seriously – but anyone who scares you with a bank card a week is selling fear, not facts. We want you to be able to trust the numbers we give you.
What the Swedish authorities say
The sober verdict comes from the authorities. The Swedish Food Agency (Livsmedelsverket) has assessed what is known about microplastics in, among other things, drinking water and concluded that the knowledge is still limited – the evidence is not enough to point to a clear health risk, but more research is needed before proper risk assessments can be made.
In a similar way, the Swedish Environmental Protection Agency (Naturvårdsverket) has assessed that microplastics at today's levels probably do not pose a major risk to the environment and health in general, while there may be places and flows where the risks are greater – and that measuring and analysis methods are not yet standardised.
In other words: the authorities are not sounding the alarm, but they are not giving the all-clear either. They are saying what is true right now – we don't know enough.
Why it makes sense to play it safe
The honest answer is that nobody knows exactly how dangerous it is. But what we do know is enough to take it seriously:
- Not proven harmful at everyday exposure – nobody has shown the full chain of cause from everyday dose to disease in humans.
- Not proven harmless either – plastic is in our organs, it builds up over time, it can damage cells in the lab, and the strongest study points the wrong way.
This is exactly the kind of situation where the precautionary principle applies: when something is widespread, increasing over time and has credible mechanisms of harm, it makes sense to reduce the exposure you can easily control – without waiting for final proof. History has several examples of substances that were "not proven harmful" for a long time before the evidence arrived. Choosing to cut out unnecessary plastic costs you almost nothing, and if research one day shows the risk was small, you haven't lost anything.
If you want to understand how plastic can affect the body, we have collected the mechanisms in How microplastics can affect the body and its cells.
What we are NOT claiming: we are not saying microplastics have been proven to make you ill, and certainly not that a toothbrush alone decides your health. We are saying it is an unnecessary, daily source of plastic in your mouth – one of the few you can remove completely with zero sacrifice in everyday life. If you want to understand the toothbrush mechanism in depth, read Microplastics in toothbrushes: the chemistry behind plastic wear.
What you can actually do
You can't remove plastic from the world, but you control the everyday sources that affect you most often:
- Don't heat food in plastic – heat releases particles. Use glass or ceramic in the microwave.
- Drink tap water rather than bottled water – bottled water often contains more plastic particles.
- Air out and dust – much of what we breathe in is indoor plastic dust from textiles and plastic surfaces.
- Swap unnecessary everyday plastic for natural materials – especially things that touch your mouth and food. Your toothbrush is a small, easy first step.