The forever chemical that quietly left your floss

Sometime this year, a chemical disappeared from one of the world's most popular dental flosses. No recall, no apology — just a reformulation. The slippery polymer that gave the floss its signature glide, a relative of Teflon, was swapped for a textured fibre. The maker now says none of its flosses contain PFAS at all (Silent Spring Institute, 2026).

It's worth understanding how that happened, and being honest about both halves of the story — the reassuring half and the part that genuinely warranted concern.

A thread, pulled

In 2019, a team led by Katie Boronow at the Silent Spring Institute did something simple and clever: they measured PFAS — the "forever chemicals" — in the blood of 178 women and matched it against their daily habits. The women who used a particular Teflon-coated floss carried more of one PFAS compound, PFHxS, than those who didn't (Boronow et al., 2019).

It's a genuinely interesting study, and we'll come back to the full thing in a future Lab Note, because it reaches well beyond floss — but for now we'll borrow only the floss finding. Boronow and her colleagues made the most useful point themselves: floss doesn't need a forever chemical to work. Most of the products they tested didn't contain one. That reframes the whole question away from fear and toward something sharper — not "this is dangerous," but "this was never necessary, so why is it here?"

The honest balance: what's reassuring, and what isn't

Here is where we have to hold two true things at once, because the evidence does.

The reassuring half. A much larger study in 2025, led by Yan Jiao and colleagues, analysed blood data from 6,750 US adults and found that, overall, floss users carried a lower total PFAS burden than non-users — they had less of four different PFAS compounds (Jiao et al., 2025). The everyday act of flossing, in other words, shows no link to a higher overall forever-chemical load. And the chemist Joe Schwarcz, writing for McGill's Office for Science and Society, made the fair methodological point that the 2019 study was correlational — it couldn't prove the floss was the source, the survey only asked whether people had "ever" flossed, and some floss users actually had lower PFAS than non-users (McGill OSS, 2019). His advice was blunt and correct: keep flossing.

The half we won't soften. That same large 2025 study found one clear, consistent exception: floss users had significantly higher serum PFOA, and it survived every statistical adjustment the authors threw at it (Jiao et al., 2025). PFOA is not a trivial compound to single out. It is one of the specific PFAS named under the Stockholm Convention, the international treaty on persistent organic pollutants, precisely because of its persistence and potential health effects, and New Zealand's own health authority lists effects associated with higher PFAS exposure including effects on the liver, fertility, and cancer (Health New Zealand – Te Whatu Ora, 2026; NZ EPA, 2023). So the fair reading is not "floss is fine, move on." It is: flossing in general shows no rise in total PFAS, but a specific PTFE-coated product was repeatedly linked to a rise in the one compound serious enough to be named in a global treaty. Both of those are true. A platform that only told you the first would be doing you a quiet disservice.

It took roughly seven years from Boronow's 2019 finding to the 2026 reformulation. For most of that time the ingredient stayed in the product, defended as safe — and other PTFE-coated flosses remain on shelves today. The redemption arc is real, but it was slow, and it isn't finished.

The two things a floss label is allowed to hide

Strip away the brand names and the issue on any shelf comes down to two blanks — the same two that recur across personal care.

The first is the coating. The "glide," the "ultra-smooth," the effortless slide between tight teeth — that comes from whatever wraps the thread, and that is exactly where a forever chemical lives when one is present. A floss sold on its slipperiness that says nothing about its coating hasn't lied to you. It has simply declined to answer the one question worth asking — and given the PFOA finding, that's not a question to wave away.

The second is "flavour." That single innocent word can stand in for a long list of undisclosed ingredients, legally protected as a trade secret. Not evidence of harm — a closed door. Some brands open it; others, allowed to keep it shut, do.

Neither blank breaks a rule. That is the point. The law sets a low floor for what a label must reveal; some companies climb well above it for free, and the only way to tell who's who is to read what's there and notice what isn't.

New Zealand is, quietly, moving

The encouraging coda — stated carefully. New Zealand's Cosmetic Products Group Standard is now explicitly built on the European Union's cosmetics regulation, the strictest benchmark going, and under it PFAS are being phased out of cosmetic products: no importing or manufacturing them past 31 December 2026, no selling past 31 December 2027, all gone by mid-2028 (NZ Cosmetic Products Group Standard 2020, cl. 4; cl. 8(1)).

One precise note, because precision is the job: that standard defines a "cosmetic product" broadly enough to include products meant to clean the teeth and the mouth. Whether a given floss is captured by it is a legal classification we won't pretend to settle. But the direction is unmistakable — toward fewer forever chemicals and more disclosure.

What to actually do

Keep flossing. Every expert in every source here agrees on that, and the benefit to your gums and teeth is real and well established. Then, if you'd rather not add to your PFOA load — a reasonable preference given what that compound is — the move is simple: choose a floss that names its coating, says PTFE-free or PFAS-free, or uses a natural wax. A floss sold purely on how smoothly it "glides," with no coating disclosed, is the one the evidence says to approach with open eyes.

Not fear. Just the whole picture, weighted the way the evidence weights it.

References

This note is about disclosure and evidence, not a verdict on any brand; we name none. The Ingredient Lab holds no affiliate links, takes no advertising, and has no commercial relationship with any company mentioned. Spotted something we've got wrong? science@theingredientlab.org