How does Sus work?

What is a barcode lookup, really?

It is a catalogue match. The barcode is an identifier, so scanning it asks a database whether it has seen that number before. When the product is in the database and the entry is current, that is the fastest answer there is, and Sus uses it first for exactly that reason.

Two things break it. The product is not in any catalogue, which happens constantly with small brands, regional releases and anything that went viral last month. Or the catalogue is holding an entry written two formulas ago, because nobody is obliged to tell a database that the formula moved. A stale entry looks precisely like a fresh one.

The barcode tells you which box it is. Only the list tells you what is in the box today.

What does reading the list get you that a barcode does not?

The label itself, as it is now, on the bottle in your hand. The ingredient list is the one part of the package written under rules rather than by the marketing team. EU Regulation 1223/2009 Article 19 and 21 CFR 701.3 both require a full declaration in descending order of weight, down to the 1 percent line.

That order is the whole reason this is worth doing. It tells you whether the ingredient on the front is most of the formula or a rounding error near the preservative. The descending-order rule, and where it stops, is its own page.

What does Sus actually do, in order?

• The barcode, first. It goes to a product bank Sus keeps, and then to Open Beauty Facts, the open cosmetics database. Cheapest and fastest path, so it runs before anything else.
• The names, against the ingredient bank. Every ingredient that comes back is read against a bank of roughly 51,000 entries, built from the EU's CosIng registry, Open Beauty Facts, and a hand-curated set for the ingredients people actually ask about.
• The product's own page, when all of that misses. Sus goes looking for the ingredient list on the open web, keeps the source link, and throws the result away unless the ingredient text appears on that page word for word. An extraction that is not literally on the page does not get banked.
• The photo of the label, whenever you have one. Point the camera at the back of the bottle and the list is read straight off it. No catalogue involved, nothing to go stale.
• The grade, against your Skin ID. Skin type, goals, what has reacted on you before, what you already use. The same list can be a B+ for one face and a D for the next.

Every product Sus resolves this way is banked with where it came from, so the next person scanning that bottle gets the answer immediately and Sus does not go asking the web twice.

What does Sus refuse to do?

Guess a product it could not read. When the barcode misses, the databases miss and the web turns up nothing that holds together, Sus says so and asks for the ingredient list. A verdict on a product nobody identified is worse than no verdict, because it is confident.

Grade a bottle from its front. A photo of the front of the pack is a photo of the ad. Sus uses it to work out which product you are holding, then goes and finds the list.

Put a number on a concentration. Brands are not required to print percentages, so nobody can read a dose off a label. Position on the list is the honest signal, and it is the one Sus reports. A single universal score answers a different question, for everyone at once.

Try it on something you already own

The fastest way to see whether any of this holds is to scan the most expensive thing on your shelf and read what comes back. Three scans are free and there is no account to make first. After that it is a 48-hour pass or a subscription, priced per country and shown on the App Store before you pay for anything.

Download Sus on the App Store

Free for iPhone. Your first 3 scans are on us, no sign-up. Sus is a cosmetics tool for informational purposes. It does not diagnose or treat anything.