What the box won't tell you about your teabag

In 2018, Taylors of Harrogate decided to fix something most of its customers did not know was there. The maker of Yorkshire Tea had been testing a new plant-based teabag, thought it had the recipe right, and rolled it out across much of the range. Then, in the brand's own words, came "a total disaster." The sealing on some bags failed. They "fell apart in people's mugs, getting us all over the front of the tabloids."¹

The company pulled back. It brought in the University of Sheffield to study the bag paper, restarted its trials, and crept the rollout forward one product at a time.² A teabag, it turned out, is harder to re-engineer than it looks.

The obvious question is why a teabag needed re-engineering at all. What was in the old bag that the new one was meant to replace?

The seal you can't see

Yorkshire Tea answered that question plainly, which makes it unusual. A conventional square or round teabag is mostly paper, made from plant cellulose. But paper edges do not hold themselves shut in hot water. They are bonded by a thin web of plastic that melts when the edges are heat-pressed. "Traditionally this plastic has been oil-based (polypropylene)," the brand explains, "and our new tea bags use plant-based plastic instead (PLA)."¹

So the bag is largely cellulose, and the seal is plastic. Premium "silken" or pyramid bags go further still: those are usually not paper at all, but a woven mesh — historically nylon or PET, and more recently sometimes a plant-based plastic like PLA — plastic spun into a net.³

The seal is invisible by design. You cannot see it, the box rarely names it, and for most shoppers the only time it gets mentioned is when a brand announces it is leaving — the moment a company stops using the plastic is the moment it finally says the plastic was there.

If there is plastic in the bag, and the bag sits in near-boiling water for four minutes, the next question is simple. Does any of it come off?

The empty bag at 95 degrees

In 2019, a lab at McGill University in Montreal set out to find out. The chemical engineer Nathalie Tufenkji and the PhD student Laura Hernandez bought four commercial teas sold in plastic mesh bags. They cut the bags open, tipped out the tea, and rinsed the leaves away, so that what they tested was the empty bag and nothing else. Then they steeped the empty bags in water at 95 degrees Celsius — brewing temperature — and counted what came off under an electron microscope.³

The design is the point. With no tea inside, any particle in the water could only have come from the packaging. The polymers that came off matched the bags they tested: nylon and PET.³ Hernandez was careful about what the experiment did and did not show. "More research is needed," she said, "to determine if the plastics could have more subtle or chronic effects on humans."⁴

The number the team reported was enormous. And that is exactly where the story has to get honest.

What comes off, and how much

There is plastic in the teabag, it sheds particles into your cup when you brew it, the box usually doesn't tell you so, and what those particles do once they are inside you has not been measured. The first three of those can be shown. The fourth cannot, not yet.

The McGill team's headline figure was that a single bag released roughly 11.6 billion microplastic particles and 3.1 billion nanoplastic particles into one cup.³ That number travelled around the world. It did not survive scrutiny.

In 2020, Busse and colleagues published a formal comment in the same journal, arguing the count was inflated by two to three orders of magnitude. Their objection was technical and specific. To image the water, the team dried it onto silicon wafers; in drying, soluble substances that had leached out of the bag — mostly short-chain manufacturing by-products called oligomers — crystallised on the wafer. Those crystals were then counted as if they were solid plastic particles.⁵ Five years later, Germany's Federal Institute for Risk Assessment (BfR) ran its own experiments and reached the same conclusion. It judged the McGill sample preparation unsuitable and found that most of what had been counted was, in its words, "apparently not microplastics, but so-called oligomers."⁶

But the recount did not find zero. Using micro-Raman spectroscopy, which reads the chemical signature of each particle one by one rather than counting a dried layer, researchers — including BfR scientists — counted only the genuine microplastic particles larger than one micrometre: between 5,800 and 20,400 per bag, a figure BfR's 2025 assessment confirmed.^5,6 So the count that survived chemical confirmation is thousands of particles per bag, not billions — the rest of McGill's headline was mostly the oligomer miscount already named above. The very smallest, sub-micron particles were not re-counted to a firm number either way. Before-and-after electron-microscope images cited in BfR's assessment also point to where these particles came from. Most were not created by the hot water tearing at the bag. They had already been sitting on the bag's surface, and brewing washed them partly off.⁶ Thousands is not nothing.

Thousands of real particles still come off into the cup. A team in 2024 asked the next question: where do they go?

Into the cell

At the Universitat Autònoma de Barcelona, the Mutagenesis Group characterised the particles released from bags made of three materials — polypropylene, cellulose, and nylon-6 — and then exposed human intestinal cells to them. The mucus-producing cells took up the most particles, and the particles were observed entering the cell nucleus, the compartment that holds DNA. The work was published in Chemosphere in late 2024 and announced by the university that December.⁷

It is worth being precise about what this is. It is uptake in a dish: human cells in a lab, taking in particles from teabags. It is not disease, and it is not a finding that teabags harm anyone. It is one careful step along the pathway, watched under a microscope. The team's own call was for "standardised test methods."⁷ That call is not generic housekeeping: the nucleus is where DNA is housed, so a particle observed inside it sits next to the machinery that mutations act on. That proximity establishes no harm — but it does name the specific test the field has not yet run, which is why the group asked for standardised methods. In-vitro work to date does show particle uptake, but it has not demonstrated disease risk. What remains unestablished is narrower and more specific: whether these particles are genotoxic or mutagenic at the doses and over the years people actually drink them, and what happens to them once they are inside the body. That question — genotoxicity and in-body tracing at real-life exposure — has not been answered either way.

So a lab can see the particles and watch them enter cells. Could a shopper see any of this on the box?

The box doesn't have to tell you

Mostly, no. Food-labelling law requires a product to list its ingredients and flag allergens. The teabag itself is treated as packaging, not as an ingredient, so its material composition is not something the box is required to state.⁸ That is a reading of how the rules are structured, not a quoted exemption — but it matches what you find on the shelf, which is that the bag's plastic is almost never named.

The first binding rule that touches this lands in the future. Under the EU Packaging and Packaging Waste Regulation, Article 9, teabags must be compostable under industrially controlled conditions from 12 February 2028.⁹ Even that rule does not require the box to tell you what the bag is made of today; it requires the bag to meet a composting standard later.

The gap shows up in how brands have talked about their own bags. In 2018, PG Tips switched away from oil-based polypropylene to a plant-based material, cornstarch, for its bags.¹⁰ Clipper, the same year, announced what it called the world's first plastic-free teabag, made from abaca fibre, cellulose, and PLA.¹¹ But PLA is itself a bioplastic — made from plants rather than oil, but plastic all the same. The "plastic-free" claim meant free of oil-based plastic, not free of all plastic, a distinction the shopper is left to work out.¹² The pattern is the same in both cases: the plastic gets named at the moment the brand is announcing it is leaving it.

There is one honest exception worth naming before the close.

Where disclosure does exist

Teapigs names its material. Its pyramid bags, which it calls "tea temples," are made from Soilon, a corn-starch PLA that resembles a nylon mesh, and the bags are heat-sealed. In 2018 Teapigs became the first tea brand to carry the Plastic Free Trust Mark.¹³ So disclosure is possible, and it exists — at the specialist end of the shelf, from a maker that tells you what the bag is and uses a non-fossil polymer.

The honest catch is one line long. "Compostable" PLA only breaks down under specific conditions: the European standard, EN 13432, certifies breakdown under industrial composting, which sustains heat well beyond what a domestic compost heap reaches.¹⁴ A garden bin largely will not break it down. The good replacement still carries a claim that does not hold in an ordinary kitchen.

So the particles are real, mostly undisclosed, and now demonstrably small enough to enter a cell. The last honest question is where they end up.

The open door

Micro- and nanoplastics have been found inside human bodies. In 2021, a team led by Antonio Ragusa in Rome reported the first detection of microplastics in human placenta — twelve particles across four of six placentas examined, including polypropylene — in a paper titled "Plasticenta."¹⁵ In 2022, Heather Leslie and colleagues at Vrije Universiteit Amsterdam reported the first detection and quantification of plastic particles in human blood, in samples from twenty-two healthy adult donors.¹⁶

What these studies show, and do not show, has to be said plainly. They establish that micro- and nanoplastics reach the human bloodstream and the placenta. They do not show that teabag particles in particular get there, and they do not show that any of it causes disease. The placenta and the blood are a telling parallel to the cup, not a documented chain from one to the other. No published study has yet isolated a teabag-derived particle inside a human body and traced what it did.

The regulator's own verdict holds both halves at once, and it is worth quoting in full rather than picking the comfortable side. The BfR judged that, on current knowledge, a health risk from the microplastics released by teabags is unlikely — and, in the same assessment, that "due to insufficient data, it is not yet possible to provide a full assessment of the effects of microplastics on the intestinal barrier or the human body."⁶ That is a notable pairing. The "unlikely" here is not the output of completed dose-response studies at the amounts people actually drink; it is a default position held while the data to assess the question properly does not yet exist. Unlikely, and unassessed, are different things — and the same assessment says both.

That is the honest edge. The particles are real, they come off in the cup, the box is not required to tell you, and the question of what they do inside you is not answered — it is unmeasured. If a study one day isolated teabag-derived particles in human tissue — and found no effect at the doses people actually drink, or found one — that would change this picture, and we would say so either way. As of now, we are not aware of such a study in either direction.

What you can do today does not depend on that missing study. Turn the box over. If it says "plastic-free" with no further detail, that usually means free of oil-based plastic, not free of bioplastic. If it says "biodegradable" or "compostable," check whether it means a council food-waste collection rather than your garden heap. If it names a polymer at all — polypropylene, nylon, PET, PLA — you are holding one of the rare boxes that tells you. Loose-leaf tea in a paper filter or a metal infuser takes the sealed bag out of the equation entirely.

Plastic particles have turned up in sampled human blood and placenta. Whether teabag particles are among them, and whether they do anything, is the next question — and the next piece.