Solid matter isn't as solid as you think
Take a few coins, hold them tightly in your hand for a while and rub your fingers. If you then put your finger in a sensitive enough instrument, you will find traces of copper and nickel on your skin. The metal has moved across – without you feeling a thing. The same happens every time you smell an orange: the scent is literally molecules that have come loose from the peel and flown into your nose.
The point: a "solid" material is really a tightly packed crowd of atoms held together by bonds – and the surface is constantly losing a few of them. Hard, strongly bonded materials (metal, stone, minerals) give off very slowly. Soft materials with weaker bonds give off much faster. And that's where plastic comes in.
Plastic is tangled chains – and it loses pieces easily
Chemically, plastic is a polymer: long carbon chains, tangled like cold spaghetti and largely held together by weak forces between the chains (van der Waals forces). Compare that with the mineral in tooth enamel, which sits in a hard, ordered crystal lattice. The spaghetti gives way long before the crystal does.
Several everyday processes also speed up how quickly plastic breaks down and sheds particles:
- Light (UV): high-energy light particles cut the chains (photodegradation). The plastic becomes brittle, yellows and flakes – think of how an old plastic toy on a windowsill crumbles.
- Heat: more heat = more molecular vibration. The chains move, slide apart and soften, which makes them easier to tear loose.
- Scraping & friction (mechanical wear): pure physics – rub something soft against something hard and tiny particles wear off. Exactly what happens when a bristle meets a tooth.
- Oxygen & water (oxidation): react with the chains and weaken them chemically over time.
That is why a plastic toothbrush eventually gets splayed, split bristles – you can see the material fatigue with the naked eye.
The tooth always wins: enamel vs plastic
This is where it gets uneven. Tooth enamel is the hardest material in the body – around 5 on the Mohs scale, actually harder than steel (but also brittle), and made of the mineral hydroxyapatite. A plastic bristle is soft by comparison.
When two materials rub against each other, it is the softer one that wears. The kinetic friction (the friction of movement as the brush sweeps back and forth) therefore tears tiny particles off the bristles – not off your teeth. And since you do it twice a day, year in, year out, that adds up to a lot of small occasions.
This isn't just theory – two studies have captured it directly. When a Chinese research team (2025) simulated brushing on an artificial dental arch, they saw under a scanning electron microscope how the bristles crack, fray and form ragged protrusions (so-called burrs) that come loose – exactly the mechanism we have described (bending, twisting, friction) – and that the release increases the longer the brush is used. An Australian Raman study (2023), in turn, estimated that a single brushing session can release thousands of plastic particles (around 6,600 nylon particles in their measurement).
Your mouth is not a passive surface
And the particles are released in an unusual place. The inside of the mouth is a mucous membrane – one of the body's most absorbent surfaces, so good at letting substances in that we deliberately place some medicines under the tongue. Unlike the skin, it is built for absorption, not for keeping things out.
That raises an obvious question: can the particles that wear off actually be absorbed there? The answer depends entirely on how small they are. We have given the mucous membrane its own article: Your gums – the body's hidden absorption surface.
How small is "too small"? Size decides everything
Size decides what a particle can do. Most particles a toothbrush sheds are "large" in this context: big enough to be swallowed or spat out. For a particle to penetrate tissue – pass through the lining of the mouth or into cells – it has to be far smaller, down at nano size. And that really is small: a micrometre (µm) is a thousandth of a millimetre, while a nanometre (nm) is a millionth of a millimetre – another thousand times smaller. It is the small tail of the very tiniest particles that is chemically interesting – and also the hardest to measure.
What the Chinese study shows about size and hazard:
- The Chinese study found that 63% of the particles were smaller than 100 µm (0.1 mm), and that nylon bristles produced an ever larger share of the smallest particles the longer the brush was used.
- The hazard also depends on the type of plastic. The same study calculated a polymer hazard index (PHI). There, nylon came out as medium risk (PHI ≈ 8.9) – higher than the other common brush plastics. And nylon is exactly what the vast majority of plastic toothbrushes have in their bristles.
The honest limit of what we know: the figures vary with the measuring method (from "thousands per brushing" to millions per year – partly the same thing expressed differently), so treat them as a direction, not an exact number. And most importantly: none of the studies could measure the nano fraction itself – the filter stopped at 0.45 µm, so anything smaller slipped past the measurement. That means the share small enough to actually pass through the mucous membrane has not been measured; it is below the detection limit. That in turn could mean the real number of particles released is larger than what can actually be measured – but that has not been proven at present.
Where do the particles go?
What about the particles that are swallowed? They clearly don't stay in the digestive tract. A study in Nature Medicine (2025) found micro- and nanoplastics in the liver, kidneys and brain – with by far the highest levels in the brain, where the particles appeared as small shards of just 100–200 nanometres. Levels were also higher in 2024 than in 2016, suggesting that plastic builds up in the body over time. In other words: the very smallest particles seem able to get almost everywhere.
What they do there is something research is still young on. Reviews describe mechanisms seen in the lab – that very small particles can trigger inflammation, cause oxidative stress and even enter cells – but the step to "this is how much everyday exposure harms a person" has not been taken.
What we are NOT claiming: we are not saying your toothbrush has been proven to make you ill. Each link in the chain has support (plastic wears → sheds particles → microplastics are found in blood and organs → particles can affect cells), but nobody has yet measured the full chain of cause all the way – from your particular brush, via uptake in the mouth, to build-up in the body.
At the same time: we think it is a reasonable line of reasoning. Each individual step is documented, so it would be strange if they weren't connected at all. That nobody has yet shown the whole circuit is probably because the field is so new – the first findings of plastic in blood and organs are only a year or two old, and tracking a specific particle from a toothbrush all the way into a cell is extremely difficult. We therefore treat it as a well-founded question of caution, not a proven fact. And the conclusion is the same either way: it is an unnecessary, daily source of plastic that is easy to remove.
Don't wait for the research
The whole chain may not be proven yet – but the direction is clear, and swapping out a daily source of plastic costs you nothing in cleanliness. Don't wait for the research to catch up. Make the swap today.