How Scoring Works

Dose, not presence: why the amount of an ingredient decides what it does

Most ingredient apps answer one question: is this ingredient on the label? That question has almost nothing to do with what the ingredient will do to your skin. The one that matters is how much of it is in there.

Yarai is a free iOS and Android app that scores skincare ingredients by how much is in the formula, not just whether they appear. This piece explains what that actually means, how a label can tell you anything about amounts at all, and where the method runs out of road.

The problem with a yes or no answer

Take phenoxyethanol, a preservative in a very large share of the products in your bathroom. The EU permits it up to 1 percent. At that level it is doing a real job, which is stopping your moisturiser from growing bacteria. Near the end of an ingredient list it might be at a tenth of that.

An app that rates by presence gives you the same flag in both cases. Same colour, same warning, same nudge to put the product back on the shelf. It is not that the flag is too harsh or too lenient. It is that the flag is answering a question you did not ask.

This is also why people stop trusting these apps. If half your shelf lights up red, the red stops meaning anything, and the one product that genuinely deserved a second look gets scrolled past with the rest.

What a label is legally required to tell you

Here is the part most people do not know, and it is the whole foundation of dose-aware scoring.

Under US labeling rules (21 CFR 701.3) and the EU Cosmetics Regulation, ingredients present at more than 1 percent must be listed in descending order of concentration. Ingredients at 1 percent or less may follow in any order. Colorants are listed under their own separate rules rather than by concentration.

Read that again, because two useful things fall out of it.

The first: ordering at the top of a list is not a stylistic choice by the brand. It is a regulatory requirement, and it carries real information. If an active appears third, there is more of it than whatever is fourth. That is the difference between a product built around an ingredient and one where the same ingredient is a rounding error added for the label.

The second, which is the honest half: below 1 percent the ordering requirement stops. Brands can arrange that tail however they like. So the signal is strong near the top of a list and fades as you go down it.

Why "active at the bottom of the list" is worth noticing. A brand can put a celebrated ingredient on the front of the box while including it at a fraction of a percent. Both things are true at once: it is in there, and it is not doing much. Presence-based rating cannot see the difference. Ordering can.

How Yarai turns position into an estimate

Yarai reads the ingredient list, takes each ingredient's position in it, and converts that into a rough concentration band. The bands it uses are deliberately coarse, because pretending to more precision than the label supports would be the same dishonesty in a different direction:

That estimate is then checked against what is actually recorded for that ingredient. Yarai's library holds a safe threshold for 178 ingredients and a specific EU maximum concentration for 38 of them, taken from EU cosmetic regulation. Salicylic acid is capped at 2 percent. Methylparaben at 0.4 percent as a single ester. Phenoxyethanol at 1 percent.

Where a threshold exists and the estimate sits below it, the penalty is zero. An ingredient inside its regulatory limit, doing the job it is in the formula to do, is not a problem, and scoring it as one would be theatre. Where the estimate runs past the threshold, the penalty scales with how far past it goes, capped at twice the base penalty so a single ingredient cannot swallow an entire score. Where no threshold exists and the ingredient carries known risk, the penalty scales with the estimated amount instead.

Scores start at 100 and penalties come off. The full mechanism, including how severity is weighted, is on the scoring methodology page.

Dose-awareness is not a way of saying everything is fine

This is the misreading we most want to head off, because it would make the whole approach worthless.

Judging by amount is not a softer setting. It cuts in both directions, and the second direction matters more than the first.

Methylisothiazolinone is a preservative that Yarai records with a safe threshold of 0.0015 percent. That is not a typo. It is restricted at concentrations far below one percent precisely because it is a potent sensitiser, and the amount at which it causes trouble is tiny. Formaldehyde sits at an effective threshold of zero. Hydroquinone at 0.02 percent.

An app that only asks "is it present" gets these backwards in both directions at once. It over-warns about the preservative that is well inside its limit, and it under-warns about the one that matters at a thousandth of a percent, because to a yes-or-no rating those two are the same event.

Being accurate about dose sometimes means saying a product is more worth a second look than a simple ingredient count would suggest. That is the point. The goal is not a friendlier score, it is a score that tracks what is actually in the bottle.

The honest limit

An ingredient list gives order, not percentages. Nobody outside the lab knows the exact concentrations in your bottle, because brands are not required to publish them and generally do not.

So everything above is an estimate. It is strongest near the top of a list, where ordering is legally required to follow concentration, and it is weakest in the tail below 1 percent, where the ordering requirement stops and a brand can arrange things freely. Yarai's score is honest math built on that ordering. It is not a measurement, and it was never meant to be a diagnosis.

We would rather tell you that than let a number look more certain than it is. Use it the way it is actually good for: comparing two products side by side, catching the thing on a label worth a second look, walking into a shop knowing which question to ask.

Has anyone else done this?

We checked the public descriptions of the other well-known ingredient scanners in September 2026, reading what each one says about itself on its own site and its own app store listing. None of them describes scoring by estimated concentration. They describe barcode lookup, databases of rated products, safety bands, and routine tracking, and several do those things at a scale we do not.

We are not going to tell you we are the first app ever to think about dose, because that is a claim about every app that has ever shipped and we cannot check it. What we can say is narrower and verifiable: we looked, on a date we have written down, and we did not find another one describing this. If you find one, tell us and we will correct this page.

What it changes in practice

Three things, if you use the app this way:

A flagged ingredient becomes a question, not a verdict. Yarai shows you which ingredients moved the score and roughly where they sit in the formula, so "this has a preservative in it" becomes "this has one near the top of the list, and here is its limit."

Comparing two products starts to work. Two moisturisers with identical ingredient lists in different orders are genuinely different products. A presence-based rating scores them the same.

You stop rebuilding a routine that was fine. Most of what gets flagged by binary ratings is inside its regulatory limit and doing its job. Knowing which flags are real is what makes the real ones useful.

If you want to see the underlying data rather than take our word for it, every ingredient we hold a threshold for is published in the ingredient library, and every interaction rule with its severity and source is in the conflict library.

Common questions

What is dosage-aware ingredient scoring?

Dosage-aware scoring judges an ingredient by roughly how much of it is in the formula rather than by whether it appears on the label at all. Yarai estimates concentration from an ingredient's position in the INCI list, then compares that estimate against the concentration limits and safety thresholds recorded for that ingredient. A preservative at a trace level and the same preservative at an active dose get different verdicts.

Does the order of a skincare ingredient list mean anything?

Yes, above one percent. Under US labeling rules (21 CFR 701.3) and the EU Cosmetics Regulation, ingredients present at more than one percent must be listed in descending order of concentration. Ingredients at one percent or less may follow in any order, and colorants are listed under their own separate rules. So the ordering is reliable information near the top of a list and much weaker toward the bottom.

Does dosage-aware scoring mean ingredients are fine in small amounts?

No, and that is the common misreading. Dose-awareness cuts both ways. Some ingredients are unremarkable at one percent and worth noting at five. Others matter at concentrations far below one percent: Yarai records a threshold of 0.0015 percent for methylisothiazolinone, a preservative restricted specifically because it sensitises at tiny amounts. A presence-only rating gets both of those wrong, in opposite directions.

Can an app know the exact concentration of an ingredient?

No. Nobody outside the lab can, because brands are not required to publish percentages. An ingredient list gives order, not amounts. Estimating concentration from that order is an estimate, strongest near the top of a list and weaker toward the bottom. It is a better estimate than ignoring order entirely, and it is still an estimate.

Try Yarai. Free on iOS and Android.

App Store Google Play