What Are Microplastics, Exactly?

Microplastics are plastic fragments under 5 mm across, shed from synthetic clothes, tyres and broken-down waste. 

We tend to think about them as an ocean problem. Plastic bottles bobbing about, turtles and seagulls tangled in netting. If we do at all, that is. And yes, there's some truth to that. But it's a reductionist view. The reality is far more alarming. They're in our water, soil and air.

A good share of plastic pollution, unfortunately, starts much closer to home – in the washing machine, and in the clothes we're wearing right now.

What Counts as a Microplastic

Size is the only test. A microplastic is any piece of plastic under 5 mm across – about the size of a pencil eraser. The UN Environment Programme (UNEP) uses a wider range, from 1 nanometre up to 5 mm, which tops out at roughly the width of a wedding band. Below that, there's nanoplastic, the dust-sized stage that's hard to even measure.

No single shape or specific type. Fragments, fibres, beads, pellets – if it's plastic and tiny, it counts.

Plastic debris gets sorted into size bands, and microplastics are only one rung. Here's the whole ladder, smallest first.

Class	Size	Roughly the size of
Nanoplastic	Measured in nanometres	Dust, or smaller
Microplastic	Under 5 mm	A speck of dust up to a pencil eraser
Mesoplastic	0.5 cm to 5 cm	A pea up to a bottle cap
Macroplastic	5 cm to 50 cm	A takeaway tub, a drinks bottle, a carrier bag
Megaplastic	Over 50 cm	Fishing nets, crates, buoys

So where do the small ones come from? Two ways, to begin with.

Made Small or Broken Down

Scientists sort microplastics into two groups.

• Primary microplastics – made small on purpose. Microbeads in face scrubs are the classic case, and Plymouth researchers found a single use of an exfoliator can release up to 94,500 of them. Industrial pellets and abrasives count too.

• Secondary microplastics – these start big. Think about discarded plastic waste you likely encounter everyday. A carrier bag, a takeaway tub, a tyre, a polyester jumper – each wears, cracks and fragments into smaller and smaller pieces. UNEP says most microplastics out there are secondary.

Fibres from the wash sit on the line between the two. Some papers class them as primary, while UNEP counts polyester clothing as secondary.

We've gone ahead with UNEP – the fibres come off a finished garment, so it's a bigger item wearing down.

Either way, they end up in the same place. And that's the problem.

Where Microplastics Come From

Washing machines get the attention, so it's easy to assume they're the main source. Sure, they're a big one. That doesn't make them the only one.

The most thorough breakdown comes from a 2017 report for the International Union for Conservation of Nature (IUCN), by Julien Boucher and Damien Friot. They modelled where primary microplastics reaching the ocean come from and landed on about 1.5 million tonnes a year. Their central estimate splits it like this.

• Synthetic textiles – about 35%. Fibres shed in the wash.

• Tyres – about 28%. Synthetic rubber, worn off the road every time we drive.

• City dust – about 24%. The everyday wear and tear of towns and cities. The report calls its own method here simplistic, so it's the least certain figure of the lot.

• Everything else – under 13%. Road markings, boat paint, plastic pellets and personal care products like face scrubs, which come to about 2%.

Look down that list and the pattern is hard to miss. It's all friction on plastic. Fabric rubbing in a drum, rubber on tarmac, paint flaking off a hull. Nobody pours these into the sea. They're what plastic does when we use it. Shedding is how a synthetic fabric ages, not a defect.

A few caveats. This may be a model, but it does demonstrate important tendencies. It also covers primary microplastics reaching the world's oceans, so it says nothing about, say, a single river. 

And the textile share moves depending on who's counting – the European Environment Agency puts the global figure at 16% to 35%, and around 8% for Europe.

That's why Plymouth's UK number looks so different. Their estimate that tyre wear makes up 65% of the microplastics reaching UK surface waters answers a different question, about a different place.

Textiles are still a big piece, and one we can do something about. They're just not the whole story.

What One Wash Sends Down the Drain

In 2016, researchers at the University of Plymouth put polyester, a polyester-cotton blend and acrylic through a domestic washing machine. It was one test on one machine, but the headline is hard to ignore: they estimated that a single 6 kg load of acrylic could release over 700,000 fibres. A review of the wider research puts it at up to 1,900 fibres from one synthetic garment.

Different yardsticks, same story. One counts a whole load, the other a single garment, so the numbers were never going to match. Both say a normal wash sheds thousands of plastic fibres, and sometimes far more.

Those fibres are thinner than a human hair, which is how some small plastic particles slip through washing machine filters and water treatment plants, and end up in rivers and the sea. Treatment does catch the bulk of them – studies put removal at more than 90%. 

That may sound reassuring. But 90% of a very big number is still a very big number, and that figure covers microplastics in general. Fibres this fine still get through.

Biggest Shedders Among Fabrics

Polyester, nylon and acrylic – the most popular choices for clothing. The reason they shed is simple. They're plastic.

A synthetic fibre is plastic drawn out into a thread. Every wash, the rubbing against other clothes and the drum wears tiny pieces off it, and every piece is plastic. 

In the Plymouth tests, polyester and acrylic both shed significantly more than the polyester-cotton blend. Less plastic in the cloth, fewer plastic fibres in the water.

Where It All Ends Up

Here we'll stick strictly to what's been measured.

• Rivers and sea. Washing fibres travel through the drain to rivers and oceans – one route into what we'd call water pollution – and a 2015 study of Arctic Ocean water, covered in that review, found fibres made up 95% of the particles.

• Plankton and soil. One study cited by UNEP found microplastics can slow the growth of phytoplankton, and a report says they can make soil less fertile. We've covered soil pollution separately.

• Animals. Aquatic species such as plankton and mussels eat many of those fibres, causing health effects.

• Indoor air pollution. Easy to forget. A 2025 University of Adelaide review estimates 100 to 1,000 particles a day from indoor air, against 10 to 100 from bottled water and 1 to 10 from seafood. They're estimates, but by particle count, the air in our homes tops the list.

So no, it isn't just an ocean problem. Microplastics turn up in soil, rivers, air and food. It's one of several kinds of pollution, too – our guide to the five main types covers the rest.

What about further up the food chain? Scientists predict accumulation, but it still needs research. So, we'll leave it there for now.

Why It's a Problem

What we do know for sure is that microplastics harm wildlife, and researchers have measured it. What's still being worked out is how much, and in which species. Three routes keep coming up.

• They get eaten. Animals swallow them, mistaking them for food or taking them in with it. A 2018 analysis of studies on fish and aquatic invertebrates by Carolyn Foley and colleagues found the most consistent effect was animals eating less of their natural food when microplastics were around. Some species also grew less, reproduced less or survived less. Plenty of results were neutral, so it varies a lot between species. Tiny animals like zooplankton may be especially vulnerable – and the rest of the food web depends on them.

• They carry chemicals. Pollutants that don't mix with water tend to cling to plastic, and plastics can contain chemicals added when they're made. A 2009 review in a Royal Society journal by Teuten and colleagues found those chemicals can pass from plastic into animals. In one feeding study, PCBs – industrial pollutants – moved from contaminated plastic into seabird chicks.

• They give microbes a ride. Microplastics can act as a host for microorganisms, and pathogens and parasites have been found on them.

Add the findings from earlier – slower plankton growth in one study, less fertile soil in a report – and they point the same way.

Then there's the part no study needs to settle. Plastic doesn't just go away once it's in the water – Plymouth's estimate is hundreds or even thousands of years. What we release stays, and it adds to what's already there. Even if each particle does only a little damage, a pile that only ever grows is a problem in itself. That last point is our reasoning, not a measured result. You can find out exactly what happens to plastic in the ocean in a separate post.

Are Microplastics Harmful to Humans?

For people, the honest answer is that we don't know the true health impacts yet.

What we can measure is exposure. A 2019 study of the American diet by Kieran Cox and colleagues estimated that Americans take in 39,000 to 52,000 particles a year from food and drink, and 74,000 to 121,000 once breathing them in is counted. The authors say those are likely underestimates. 

As for what that does to us, the European Food Safety Authority and the UN Food and Agriculture Organization (FAO) concluded that large microplastics are likely excreted, and that absorption of the smallest ones is limited. And the World Health Organization's 2019 assessment of drinking water, which looked at nine studies, put the risk at low, but not zero.

Bad for wildlife. Unresolved for us. And unresolved isn't the same as safe – WHO itself said drinking-water research only began in 2018.

What People Get Wrong

Three ideas come up again and again.

"It's a new problem."

Not quite. Plymouth's Professor Richard Thompson coined the term in 2004, in a paper called "Lost at Sea: Where Is All the Plastic?" Microbeads first appeared in personal care products about 50 years ago, and as recently as 2012 the issue was still relatively unknown. We've been making this for decades. We only recently started measuring it.

"Washing less solves it."

It helps a bit – fewer washes, fewer fibres. But shedding is built into the fabric, not the laundry routine. Even clothes drying on a line can release fibres. And laundry is only part of the picture – tyre wear tops the UK estimate we covered above.

"A filter catches them all."

Partly. The finest fibres slip through filters and treatment plants, as we saw above. A filter on the machine helps. It won't catch everything.

How to Reduce Microplastics – Quick Laundry Checklist

You can't stop it, but you can turn it down.

• Wash bag. A fine mesh bag holds back some of the fibres before they leave the drum.

• Filter. One fitted to the machine can catch some fibres on the way out.

• Lower spin speed. Gentler tumbling means less rubbing.

• Wash when it's needed. Not out of habit.

None of these stops shedding. They catch it or slow it.

Choosing Materials That Don't Shed

The real fix sits upstream – buying less plastic in the first place.

Natural isn't flawless. The NHM's Alex McGoran warns that if we all switched to organic clothing, the land and water needed to grow the cotton would be immense. Fair. But that's a resource we can measure and replace, not plastic that outlasts all of us. We've actually looked at how sustainable cotton is if you want the detail.

Start with what sits closest to the floor. Any absorbent bath mat spends its life trodden on, soaked and thrown in the wash – and if it's polyester, it sheds every time. 

We've weighed up synthetic bath mats before.

A stone bath mat is a different class altogether – it's rock, so there's no thread to wear down and nothing to put in the machine. Our diatomite bath mat works that way: it pulls water in, lets it go again, and has no fibres to shed. 

For towels, organic cotton or bamboo eco towels do the job without leaving plastic fibres behind.

Catching fibres helps. Not making them is better.