What does a comedogenic rating of 0 mean?

A 0 means the ingredient did not produce comedones in the testing model used for that rating. It is the lowest-risk tier, but it is not a guarantee for every person.

Why do two websites rate the same ingredient differently?

They may use different testing methods, different source studies, different concentrations, or simply different judgment. There is no single standard, so compare sources rather than trusting one.

Is the rabbit ear model accurate for human skin?

It is useful as a screening tool, but it has limits. Rabbit ears are more sensitive than human skin, and ingredients were often tested undiluted, so results can overstate real-world risk.

How the Comedogenic Rating Scale Works and Its Limits

Q: Who created the comedogenic rating scale?

The widely cited 0 to 5 scale comes from work by J. E. Fulton and colleagues, including a 1989 survey of skin care ingredients using the rabbit ear model. Other labs and sites have since built their own versions.

The short answer

The comedogenic rating scale runs from 0 to 5, and it is a screening tool, not a verdict. Higher numbers mean an ingredient has been more likely to produce clogged pores in the testing model behind the rating. The most widely cited version traces back to J. E. Fulton’s work, including a 1989 survey of skin care ingredients using the rabbit ear model. The checker uses this kind of rating to flag ingredients, but the number alone does not tell you how a product will behave on your face. This is informational, not medical advice.

Where the numbers come from

Fulton’s 1989 survey tested many commercial ingredients on rabbit ears, a model where comedones form in a way that researchers can score. The scoring was then translated into a 0 to 5 scale. Fulton later revised the assay with more specific procedures, aimed at reducing disagreement between laboratories. Other researchers and companies have since published their own lists, and many consumer sites copy or adapt them.

The chain matters. A rating on a website may be a copy of a copy of a study. That is why two sites can show different numbers for the same ingredient, and why it is worth knowing where a rating comes from before you rely on it.

Why the scale has limits

The rabbit ear model is more sensitive than human skin, so some ingredients may be flagged that do not clog human pores in everyday use. Ingredients were often tested undiluted, while a product might contain them at a small percentage. The model also cannot capture how a full formula behaves, including emulsifiers, fragrances, and the way the product is applied. A single ingredient can look very different once it is mixed with others.

There is also no formal standard for what “comedogenic” means. The FDA does not define “non-comedogenic” for cosmetics, so the phrase on a label is a marketing claim, not a regulated test result.

How to use a rating wisely

A rating is most useful as a starting point. A high number tells you to look more carefully at the product, test it, and watch your skin. A low number is encouraging but not a promise. Think in patterns rather than single items:

Check the full ingredient list, not just one flagged item.
Consider where the ingredient sits on the label, since amount affects risk.
Compare two or three sources for the same ingredient.
Trust your own history. If you broke out after a product, that matters more than a chart.

The free pore-clogging checker shows the rating and source notes for each flagged item, so you can judge the context yourself rather than reading a number in isolation.

Why one ingredient is not the whole story

Acne is a multi-factor condition involving sebum, follicle shape, bacteria, inflammation, and sometimes yeast. A comedogenic ingredient can add to the problem, but it rarely acts alone. Two people using the same moisturizer can have very different results. Likewise, a product with an ingredient rated low can still bother a reactive face if the formula is heavy or the texture is occlusive.

For this reason, use the scale to narrow your choices and then test one change at a time. If the flagged item is in a product that you love, a patch test is a better first step than an immediate switch. For fungal acne, which behaves differently, the fungal acne checker page explains how to use the separate toggle.

Common mistakes

Reading a rating as a guarantee. It is a screening signal.
Treating 0 as proof of safety. Some low-rated ingredients still cause problems in certain formulas.
Assuming all sites use the same method. Check the source notes.
Ignoring context. Concentration, base, and application all change the outcome.

Where to go next

Use the free pore-clogging checker with a product you own, then read Comedogenic Ingredients List for the families that come up most. For a specific example, see Is Isopropyl Myristate Comedogenic? or Is Coconut Oil Comedogenic?. The FAQ covers how the checker builds its flags and what it cannot tell you. A dermatologist can help if breakouts persist.