Last updated: September 19, 2026
This page says where Piel's information comes from, what a verdict is worked out from, who reviews the knowledge behind it and how far that review has got, and what Piel will not tell you. It is written to be checked against the app, not to sell it. Piel is made by Kan Consult s. r. o. in Slovakia.
When you open a product, Piel reads its ingredient list and checks it against the skin profile you gave it: your skin type, whether your skin is sensitive, your goals, what you have told Piel you react to or prefer to avoid, any condition or prescription active you have recorded, and your pregnancy status. Your age is on your profile but the verdict does not use it.
The verdict looks at six things: how much of the ingredient list Piel could actually match to a known ingredient; whether any ingredient is one you have reported a reaction to or asked to avoid; pregnancy cautions; ingredients that a recorded condition or prescription active argues against; comedogenic ingredients, if you have told Piel you get breakouts; and whether the product's ingredients fit the goals you set. Each one is reported as a plain sentence with its reason, so the verdict is a list of things Piel found, not a mystery score.
The verdict has five outcomes. Looks good with your skin: nothing to flag and the ingredients fit at least one of your goals. Nothing to flag for your skin: nothing negative, and nothing that speaks to your goals either. Patch test first: at least one caution. Use with care: at least one finding Piel treats as serious, such as an ingredient you have reported a reaction to. No verdict yet: Piel could not match enough of the ingredient list to judge it. The worst finding decides the band, and a reported reaction always outranks a stated preference.
The coverage rule is the one that matters most. If fewer than half the entries on an ingredient list can be matched, Piel refuses to give a band at all rather than give one on half a formula, and it tells you how many ingredients it recognised, for example 24 of 26, so you can see how much the verdict rests on. Piel adds nothing it did not find: a product with no findings is reported as exactly that.
On the ingredient screen each ingredient carries an evidence band: well documented, worth a look, or thin data. These are not Piel's own judgement. They come from a third-party ingredient analysis service, INCI API, whose 0 to 10 score measures how thoroughly an ingredient has been assessed, not how harsh it is. Piel groups the scores into the three bands, shows a gap rather than a zero where the service has no score, and labels the analysis in the app as done by that service and not by Piel. The Halo verdict above is computed separately, from Piel's own knowledge base and your profile.
When you build a morning and evening routine, Piel checks the products against each other. A conflict is a rule between two ingredient categories, for example a retinoid and L-ascorbic acid at the same time, benzoyl peroxide with a retinoid it degrades, or two exfoliating acids in one step. Each rule has a severity, caution or avoid, and a scope, same time or same day. A rinse-off product is exempt where the rule is about leaving both on the skin, and an ingredient present only in trace amounts lowers the conflict one level. The fix is one tap: move one product to the morning, alternate nights, or keep both, and Piel records that you chose to keep both.
Reapplication timing comes from the live UV index at your approximate location, fetched by your phone directly from the free Open-Meteo weather service. Piel's own servers never see your coordinates, the app only ever asks for a coarse location, and only while it is open. At UV 0 to 1 there is no reminder; at UV 2 the interval is three hours; at UV 3 and above it is two hours; indoors it stretches to three hours, because windows still let UVA through; and reminders stop at eight in the evening.
Piel does not compile a cosmetics catalogue from scratch. What an ingredient is classed as doing, its regulatory restrictions and its identifiers come from CosIng, the European Commission's Cosmetic Ingredient Database, © European Union, used under the Creative Commons Attribution 4.0 licence. Piel standardises the names and matches them to its own ingredient records, and it refuses near matches, so no regulatory fact is attached to an ingredient nobody confirmed. The European Commission had no part in Piel and does not endorse it.
Some product names, brands, photos and ingredient lists come from Open Beauty Facts, an open database available under the Open Database License. The rest of the product catalogue is Piel's own, built up and corrected over many rounds of work. Per-ingredient evidence scores are read from INCI API and refreshed rather than stored. None of your personal information is sent to any of these sources.
The same records are published as a public ingredient glossary and a set of "can I use these together?" pages. A glossary page shows Piel's own plain-language note only for an ingredient whose note has been reviewed and stamped, and most of those stamps are a model's rather than a person's; for every other ingredient it shows CosIng's classification, identifiers and annex position, and nothing Piel has not held to the same review.
The knowledge base is the set of claims the verdict and the routine check rely on: that an ingredient belongs to a category, that it warrants a pregnancy caution, that it conflicts with another. They are data, not code: each claim is drafted, reviewed one at a time, and goes live or is withdrawn without an app update. Every claim carries who reviewed it, when, and the evidence it rests on, and a claim cannot appear in the app without a review stamp.
Here is the part most apps leave out. The claims were drafted from the public sources above by AI models, and a second model read the first one's work and rejected or withdrew what it disagreed with. That is a useful check and it is not human review. The human review is done by Kan Consult s. r. o., by hand, one claim at a time, and it started with the claims that carry the most weight: retinoids, exfoliating acids, vitamin C forms, benzoyl peroxide and the pregnancy cautions. It is ongoing, and most claims in the knowledge base today still carry a model's stamp rather than a person's. Piel has no dermatologist, pharmacist or cosmetic chemist on staff. When a reviewer finds a claim right but its stated reasoning overclaimed, the reasoning is corrected and re-signed; when a live claim is found wrong, it is withdrawn and every cached verdict is recomputed.
If you find an ingredient entry you believe is wrong, write to support@mypiel.app and say which product and which ingredient. Corrections go through the same review.
Piel Premium includes an assistant you can ask about the products you own. Its answers are written by a model run by Anthropic, processed in the United States, and it is off until you read a consent screen and turn it on. It can only read: it cannot change your shelf, your routine or your profile. When it looks something up, it asks for four reference sources, PubMed, the Cosmetic Ingredient Review, CosIng and the EU's SCCS opinions, and it names only those; what it reads to write an answer is decided by the search provider, not by Piel.
The assistant will not diagnose or name a condition, tell you what caused a reaction, tell you to start, stop or change a prescription, or declare a product safe in pregnancy, while breastfeeding, for a child, or in general. On those questions it answers within that boundary and says who should decide: your doctor, dermatologist, pharmacist or paediatrician. It will not promise a result. It refuses only questions that are not about skin, and it writes each answer as you watch, without Piel checking it first, so an answer can be incomplete or wrong. Nothing you type is stored once the answer has come back, and Anthropic does not retain it under a zero-data-retention agreement. The Privacy Policy sets out exactly what is sent and what is not.
Piel is not a medical device and does not provide medical advice. Verdicts are estimated from ingredient lists, not from reviews or tests of the product, and an ingredient list says nothing about concentration or formulation. Piel will not tell you a product is safe, will not diagnose a skin condition, and will not tell you why your skin reacted. It has no shop and no affiliate links, so the verdict has nothing to sell you. Your progress photos stay on your phone unless you turn on backup, and Piel does not claim to align them: the guide helps you frame the next photo the same way, and the comparison is yours to read.