Why this site does not use comedogenic ratings

Nearly every ingredient checker prints a number between 0 and 5. This one does not, and the reason is not caution — it is that the number answers a question nobody is asking.

Where the 0–5 scale came from

The idea that cosmetic ingredients can provoke comedones was introduced in dermatology in 1972, in the paper that named acne cosmetica. The scale people quote today descends from a rabbit ear assay published in 1984, which screened therapeutic products, cosmetics and raw ingredients by applying them to rabbit ear skin and counting the comedones that resulted.

That study is real, it is peer-reviewed, and it is the origin of most ingredient-level comedogenicity lists still in circulation. Two things happened to it afterwards. The first is that its results were copied between sources for four decades, often losing the attribution along the way, until ingredients that were never in the study acquired ratings anyway. The second is that the literature moved on, and the lists did not.

What an animal model can and cannot tell you

A rabbit ear assay is a screening tool. It is a way of sorting materials quickly, not a measurement of what a cosmetic does to a human face. The methodology literature is explicit about the limitation: a human comedogenicity assay study reports that a number of studies have pointed out the rabbit ear model’s disadvantage of overreacting to comedogenic materials.

It would be dishonest to leave the argument there, so here is the part that cuts the other way. A 1982 human upper-back assay reported that substances rated moderately to strongly comedogenic in the rabbit ear model were capable of inducing comedones in the human model. That is a real correlation, and it means the rabbit ear results are not noise. What it is not is a general equivalence between the two models: it is agreement at the strong end of the scale, which says nothing about whether an ingredient rated 2 rather than 4 means anything at all.

The finding that breaks the whole approach

In 2006, a human study applied a modification of that upper-back assay to finished cosmetic products — not raw ingredients, but products as sold — formulated with ingredients previously identified as comedogenic. It reported that those finished products were not necessarily comedogenic.

This is the single most important source behind this site, and it is the reason no ingredient-level number appears anywhere on it. An ingredient rating is only useful if it predicts something about the product in your hand. The direct test of that assumption found it does not reliably hold. Every checker that converts a list of ingredient names into a verdict about a product is performing a step that was tested and did not survive.

The practical consequence is that concentration, the rest of the formula, exposure time and whether a product is rinsed off or left on all sit between an ingredient name and an outcome, and none of them are visible on a label.

What this site reports instead

Four classes, no scale, and no aggregation. They are deliberately not ordered from good to bad, and they are never combined into a score for a product.

Reported concern
At least one cited source reports a comedogenicity concern for this name. The tier says what kind of study that was, which is usually the part that matters most.
Conflicting or context-dependent evidence
The cited sources disagree, or the classification is actively contested in the published literature. This is not a midpoint on a scale; it is a description of an unresolved argument.
No concern found in the included sources
No source included here produced a concern for this name. It is not a finding of proven non-comedogenicity, and for many records it means the corpus simply contains no assessment either way.
Not recognised or insufficient evidence
Either the name was not recognised, or the evidence is not established. Ingredients that circulate widely on comedogenic lists but have no verifiable assessment in this corpus land here rather than being classified in either direction.

The strongest product-level sentence this site will produce is a count of matches followed by a statement of what that count does not establish. There is no percentage, no grade and no risk level anywhere in it.

Why every record carries an evidence tier

An animal-model finding and a human finished-product finding are answers to different questions, so they are never averaged or treated as interchangeable. Each record states which kind of evidence it rests on.

A finished cosmetic product was tested on human skin.
A finished cosmetic product was tested on human skin. This is the only tier that answers the question people are actually asking, and it is the rarest.
The ingredient itself was tested on human skin, separately from any product containing it.
The ingredient itself was tested on human skin, separately from any product containing it. That is closer to the question than an animal model, but it is still not a finished-product result.
The material was applied to animal skin — in this dataset, a rabbit ear assay.
The material was applied to animal skin — in this dataset, a rabbit ear assay. It is a screening model, and the human-assay literature reports that it overreacts to comedogenic materials relative to human testing.
Laboratory work on cells or tissue models rather than on skin.
Laboratory work on cells or tissue models rather than on skin. It can describe a mechanism, but it cannot describe what happens on a face.
A reference or regulatory source rather than a study that measured comedogenicity.
A reference or regulatory source rather than a study that measured comedogenicity. In this dataset that most often means the source establishes only that the name refers to a recognised cosmetic ingredient.
No source in this dataset assesses this ingredient's comedogenicity.
No source in this dataset assesses this ingredient's comedogenicity. The entry exists to record that the question is open, not to imply an answer to it.

What “no concern found” does not mean

This is the class most likely to be misread, so it is worth stating bluntly. It means that no source included in this dataset produced a concern for that name. It does not mean the ingredient has been shown to be non-comedogenic, and it does not mean anyone tested it.

For a large share of records, the only citation attached is a regulatory database entry establishing that the name refers to a recognised cosmetic ingredient. That is an identity citation, and this project never treats identity as evidence about comedogenicity. Where that is the case, the honest reading of the record is that the reviewed literature contains nothing about the ingredient in either direction — which the individual ingredient pages say in those words.

Rules the dataset has to satisfy

These are enforced by a validator that runs during the build. A record that breaks one of them fails the build rather than shipping.

The whole corpus, and what each source supports

This is every source behind every classification on this site. It is a small corpus, and saying so is part of reporting it accurately. Each entry records what it does and does not support.

Limitations of this site itself

Corrections

Every record carries a stable identifier, a review date and its sources, so a disputed entry can be pointed at precisely. Corrections are made by changing the dataset and its version, not by adjusting wording in the interface.

Reviewed by: pore-checker prototype dataset compilation (not clinically reviewed).