The pair of knickers that rewrote our rulebook
We set out to score one pair of period underwear. Five scores later, the underwear was fine. Our rulebook wasn’t.
93%. Lovely. Wrong.
The first number looked wonderful. It also had nothing to say about fabric, because our rulebook didn’t ask about fabric yet. A pair of knickers scored like a glass of water.
So we added the obvious question: how far has this fibre travelled from the plant? Linen, barely at all. Polyester, all the way from an oil well. This pair’s core is 88% polyester microfibre. Score: 80%.
78%. Better maths, same blind spot.
Then we asked where it touches you. Skin that absorbs more deserves a sharper pencil. We built that in, did the working line by line, landed on 78% — and found the real problem sitting in plain sight. The People pillar scored 100. A perfect score for the person wearing it.
The PFAS-free claim had never been tested. The certificate on the website couldn’t be checked. Nobody would say how the “stays fresh” part worked. Every rule we had was correct, and together they handed a perfect score to a brand that had answered one question out of four.
Our rules were rewarding silence.
66.75%. The day we changed the ruler.
So we changed it, before we wrote a word of the page. We call it the Disclosure Default — you’ll see it on the page as Open Questions. Plainly: if we can’t find the answer, you don’t get the benefit of the doubt.
We asked the brand three things, in writing: the certificate number and what it covers, how the odour control works, whether the PFAS-free claim was tested. We gave a date. It passed.
What arrived, two days late, was a friendly email with product photos and a caption we could “just paste.” We didn’t. A reply isn’t evidence. Score: 66.75%, Worth a Pause. It’s been on the page since.
51.00%. The one we’re publishing today.
This month we tightened one more screw: when a brand doesn’t tell us what something is, we score it as the worst version that kind of product has been shown to be. Same rules, same weight, as if they’d told us.
“Naturally antibacterial” is a claim bamboo can’t keep once it’s viscose. So if the freshness works, something was added — and we score what that something has been shown to do in the wash.
PFAS isn’t hypothetical here, either. A 2025 study tested reusable period products worldwide and found almost a third of the period underwear looked deliberately treated with it (Wicks et al., Environmental Science & Technology Letters, 2025) — the same researchers noted none of these products actually need it to work.
New score: 51.00%.
What would move it?
One email. A certificate number, a lab report, a sentence about the odour control. Sending us evidence is free, always, and the number moves the same week. It has never been possible to pay us to look.
While we were in there: the rest of the drawer
Underwear was never the whole story. Pads, tampons, cups — same drawer, same questions, and we’ve been asking them of the whole category.
The pad question South Africa just asked out loud. In February, University of the Free State researchers tested pads and liners sold here for a group of chemicals called endocrine disruptors — bisphenols, parabens, phthalates. They found something in every single pad tested. Bisphenols showed up in 100% of them.
What we can’t yet tell you is how much of that reaches your body — the researchers modelled it, they didn’t measure it on real skin, and they say so themselves. SABS told Parliament in March that the pads on sale are safe. Both things are true at once, and neither one is the whole picture yet. That’s the honest sentence, and it’s the one we’re printing.
Tampons: sixteen metals, thirty products, one open question. A 2024 US study tested thirty tampon products from fourteen brands for sixteen metals. All sixteen turned up in at least one sample. Lead ran higher in non-organic tampons; arsenic ran higher in the organic ones — so “organic” isn’t the automatic pass it sounds like. A “certified organic cotton cover” only certifies the cover.
Whether any of it crosses the lining is still unmeasured — the study’s own authors say so, and medical toxicologists say there’s no evidence yet of anyone being poisoned by one. We’re publishing both halves of that, on purpose.
Cups win on the planet, clearly. Life-cycle research comparing cups, reusable pads, period underwear and disposables puts cups about 99% lower in environmental impact than a year of conventional disposable tampons. Disposables rank last, whichever way you slice it — and in South Africa, a meaningful share of that waste ends up in drains, stormwater and open ground, not landfill.
We’ve run every product we could find against the questions above, line by line, the same way we ran this pair of underwear five times. We’re not printing the numbers here — that’s what the page is for. What we will say is that the same rule holds everywhere in this drawer: silence costs points, and organic doesn’t buy a pass.
One brand came close enough to mention. Knix publishes PFAS test results going back to 2020 — every round, non-detect. What it hasn’t published is the name of the lab that ran them. We’d love to know. One name would make it the first period underwear on Shake with that question actually closed.
What this means for your drawer
- A badge is not a certificate. Look for a number you could type into a search box.
- “Stays fresh” is a question, not an answer. Ask what’s doing the freshening.
- Single natural fibres next to skin are the easiest to understand — and easy to understand is half the battle.
- We love the freedom a tampon gives you. We want the choice, and the transparency to make it. Nobody has yet measured how much crosses that lining. Until someone does, you deserve to know what’s in them — and to choose.
The label writes the score. We don’t. Only evidence moves it.
→ See the full score, the working and the open questions on the
Disclosures: Shake does not give medical advice, and nothing here says any product causes or prevents any condition. Scores follow the ShakeUp Standard Operating Manual and the scoring rulings of 17 September 2026. Sources: Wicks et al., Environ. Sci. Technol. Lett. 2025 · Blignaut, Kemp, Erasmus, Visser & Schutte-Smith, Science of The Total Environment 1018 (2026) · Shearston et al., Environment International 190 (2024) · ACMT position statement (2024) · Fourcassier et al., Cleaner Environmental Systems 7 (2022) · UNEP/Life Cycle Initiative (2021) · reported by Mail & Guardian.
