Low irritation is a 30-subject, 3-day test
What stands behind a low-irritation claim is fixed by the test menu, not by the copywriter. Korea's primary skin irritation study runs on at least 30 subjects under a 24-hour occlusive patch and closes in three days. No test returns ‘no irritation’, and Europe and the US read it in two more ways.
‘Low irritation’ transcribes a test verdict; ‘no irritation’ appears on no test menu at all. Korea's primary skin irritation study patches at least 30 subjects for 24 hours under occlusion and reads the sites 1 hour and 24 hours after removal, finishing in three days. Cumulative irritation repeats that patch nine times over three weeks, and adding sensitization pushes the study to six weeks.
A verdict, not a property
Open an irritation report from a Korean laboratory and the conclusion line reads “low irritation”. That line describes a result under stated conditions, not a property of the product. Because the conditions are written down, the claim can travel to a product page; strip the conditions and nothing is left to stand on.
“No irritation” sits elsewhere. Look down a testing institute's safety menu and there is no column that returns it. A sentence promising zero irritation reaches past the panel to every future user, so no study design reaches it either. That is the exact shape Annex 5 of Korea's Enforcement Rule rules out — wording that is partly true but leaves a broader impression.
Choosing the study fixes the calendar
Irritation work splits four ways, and the choice sets both the wording you may use and the sample timeline you have to book.
| Study | Subjects | Patch design | Duration |
|---|---|---|---|
| Primary skin irritation (low irritation) | 30+ | 24-hour occlusive patch, read 1 h and 24 h after removal | 3 days |
| Sensitive-skin irritation | 30+ | Lactic acid sting screening, then 24-hour occlusive patch | 3 days |
| Cumulative irritation | 30+ | 24-hour patch applied and removed nine times | 3 weeks |
| Cumulative irritation and sensitization | 30+ | 3-week induction, 2-week rest, then a 48-hour patch | 6 weeks |
The top two close in three days, which is why they carry most low-irritation claims on gentle bases. The bottom two run three and six weeks, and daily-use products or long-contact formats such as patches and sheet masks are where that extra design starts to matter.
Booking a launch without knowing those durations is how dates slip. A six-week sensitization study has to be scheduled before the sample is frozen, and any formula change sends it back to the start. Deciding the claim first and the study second is the cheaper order.
Who ran it is part of the condition
Results alone do not carry a dossier. A human application study has to be conducted and evaluated under a specialist physician or a hospital, or under someone with at least five years of human application testing experience at a university or a specialised cosmetics research institute, whether in Korea or abroad. A cheap certificate failing at the request stage usually fails here.
One labeling trap sits next to this. When the MFDS widened its list of prohibited expressions in January 2025, it added claims that designate or imply a medical professional's endorsement, including “for hospital use”. Stating that the study ran at a dermatology clinic is one thing; wording that reads as a dermatologist recommending the product, or as a hospital-only line, is another. Check “derma-tested” and “dermatologist recommended” copy against that line before it ships.
The same word is three different words
This is where a single global label breaks. The three markets ask for different things behind irritation wording.
| Market | Wording used | Evidence required |
|---|---|---|
| Korea | Low irritation / low-irritation tested | Human application study, filed on request |
| EU | Hypoallergenic | Evidence of very low allergenic potential by design, with known sensitisers fully avoided |
| US | Hypoallergenic | No federal standard or definition, no pre-market filing |
Europe carries the heaviest load. Its technical document tells the responsible person to avoid substances identified as sensitisers by the SCCS or other official risk assessment bodies, those classified as CLP skin sensitiser category 1, 1A or 1B, those the company itself has spotted in consumer complaints, those widely recognized as sensitisers in the literature — and those with no relevant sensitization data at all. The last item is the one that bites, because absence of data is treated as a reason to exclude.
The same document refuses to let the claim mean zero risk. It states plainly that a complete absence of the risk of an allergic reaction cannot be guaranteed. The logic that makes “no irritation” unusable in Korea is doing the same work in Brussels.
Write the claim at the sample stage
In practice, invert the order. Instead of locking the formula and writing copy afterwards, send your supplier three lines of intended wording, one per market, before the sample is approved. Whether a base already carries a finished irritation study, and whether sensitization has ever been run on it, surfaces in that one exchange.
Ask how the panel was built, too. Thirty subjects screened for sensitive skin is an easier verdict to explain to a buyer than thirty unscreened ones. Which materials are moving right now is tracked daily in today's ingredient signals, and category price bands and cost structure sit in the product planner.
In short
- “Low irritation” transcribes a verdict. The primary study is 30-plus subjects, a 24-hour occlusive patch, three days.
- Cumulative irritation takes three weeks and sensitization six. Book it before the sample is frozen, because a formula change restarts it.
- “No irritation” appears on no test menu. It reaches beyond the panel, so no design substantiates it.
- EU hypoallergenic demands total avoidance of known sensitisers, and the US has no federal definition at all. One label will not cover all three.
*Sources: Korea Ministry of Government Legislation, Easy Law — “Substantiation of cosmetic labeling and advertising” (Cosmetics Act Art. 14; Enforcement Rule Art. 23 and Annex 5), accessed 22 October 2026 / Korea Cosmetic Association, commentary on Cosmetics Act Arts. 13–14 and substantiation standards / Global Medical Research Center (GMRC), human application safety test menu, accessed 22 October 2026 / MFDS announcement on widened prohibited advertising expressions, 21 January 2025 / European Commission, Technical document on cosmetic claims (2017), Annexes III and IV / U.S. FDA, “Hypoallergenic” Cosmetics*
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Questions people ask
A human application study. The primary skin irritation test is the usual choice: at least 30 subjects, a 24-hour occlusive patch, three days end to end. Korean guidance asks you to name the testing institute, the subjects and the test period next to the claim.
A 30-subject panel supports ‘no irritation was observed under these conditions’, not ‘nobody will react’. Wording that is only partly true yet leaves consumers with a broader impression is blocked by Annex 5 of the Enforcement Rule.
The sensitive-skin irritation test screens subjects with a lactic acid sting test first, then patches them the same way. Subject count and duration match the primary test, but the panel is built differently, so the same formula can read differently.
Not directly. The EU technical document allows ‘hypoallergenic’ only for products designed to minimise allergenic potential, and requires total avoidance of known sensitisers and their precursors. That is a different dossier from an irritation report.
There is no federal benchmark. FDA states there are no federal standards or definitions governing the term ‘hypoallergenic’, and that companies need not submit proof to the agency. No standard is not the same as no liability, so the exposure sits in post-market disputes.