Is the Comedogenic Scale Accurate? Where the 0–5 Ratings Really Come From — and the 4-Week Test That Beats Them

By S. C. Aris — about the author

Last updated: 18 September 2026

Type any face oil, serum or moisturiser ingredient into a “pore-clogging checker” and you will get a number from 0 to 5. Coconut: 4. Isopropyl myristate: 5. The same plant lipid: 0 on one site, 2 on another. People screenshot these charts, cross-reference every product they own, and throw out anything with a 3 or above. It feels rigorous. The trouble is that almost nobody who uses the charts knows where the numbers came from, what was actually tested, or what the researchers who built the scale said about it afterwards. This article walks through the primary sources, in order, and ends with the test that actually answers the question you care about: will this product clog my pores?

What the scale is supposed to measure

“Comedogenicity” is the tendency of a substance to cause clogged pores, the blackheads and whiteheads dermatologists call comedones. According to the 2025 JAAD Reviews clinical review by Starzyk, Aust, Schur and Miller, comedogenic substances “promote abnormal keratinization and shedding of cells within the follicular infundibulum, leading to a keratin plug that blocks the pilosebaceous unit.” The plug starts as an invisible microcomedone and only later becomes a visible bump. If the blocked follicle stays partly open to air you get a blackhead; if it seals over you get a whitehead.

The 0–5 scale grades how much follicular plugging a test substance produced. Per the same review, most studies used a scale where 0 meant no keratin plugging and 5 meant severe comedone formation, with 0–1 considered non-comedogenic and 3 or above considered significantly comedogenic. That is the whole scale. It is not a measure of how “heavy” an ingredient is, how “oily” it feels, or whether it is natural or synthetic.

Where the numbers came from: a 50-year timeline

Every comedogenic chart on the internet descends from a small number of papers. Here they are, with what each one actually established. Sources marked “as summarised” are older papers we could not open in full and are described as they are reported in the 2025 review and the 2021 trial cited below.

Read that table top to bottom and the pattern is clear. The numbers were generated in the first decade. Every decade since has been spent qualifying them.

Five reasons the number on the chart can mislead you

1. It was measured in a rabbit’s ear

The rabbit ear was chosen because it reacts fast, not because it reacts like a human face. The 2025 review puts it plainly: “The rabbit ear model is extremely sensitive, and therefore, not everything that irritates the model will irritate the skin. Even Kligman and Mills, who originally developed this model, later acknowledged challenges with its application to human skin.” When Mills and Kligman ran their own human model in 1982, some substances that were potent comedogens in rabbits “produced little to no comedone formation in humans.” A rating of 3 on a rabbit chart is, at best, a prompt to look closer.

2. It was measured at 100% concentration

Waranuch and colleagues, writing in 2021, note that the classic ingredient lists “were conducted from testing of 100% concentration of the tested ingredients in animal models, namely rabbit ear assay.” A finished moisturiser might contain 2% of that ingredient. A chart cannot tell you what 2% does. It cannot even tell you what 100% does on a human.

3. An ingredient is not a product

This is the finding that should have ended the chart era in 2006. Draelos and DiNardo wrote that animal models had been used “with the assumption that finished formulations containing these ingredients would also be comedogenic,” and that “based on this assumption, dermatologists were presented with lists of substances to avoid.” They then tested finished products and found the assumption did not hold. Their positive control, octyl palmitate, did what it was supposed to: the mean ratio of follicles to microcomedones went from 34.29:1 to 17.90:1 after four weeks, meaning plugs roughly doubled. The finished products built with rated ingredients did not behave like their ingredients.

It cuts the other way too. The 2021 trial authors point out that even when every single ingredient is rated low, “it is possible that a formation of comedogenic substance(s) due to chemical interaction between the ingredients used occurs during the emulsification process.” Their conclusion, and the review’s, is the same: only the finished formula can be tested meaningfully.

4. It was measured on the back, not the face

Human comedogenicity assays are run on the upper back, chosen because follicles there are large and plug readily. The 2025 review flags this directly: “the majority of comedogenicity testing occurs on the upper back when the product’s intended use is on the face,” and notes that facial testing is hard to recruit for because of scent, colour and reaction concerns. The 2021 trial cites a “low correlation in comedogenic response of different areas.” If a formal back test only partly predicts your face, an ingredient rating from a rabbit ear predicts it less.

5. People are not interchangeable

The clearest illustration is buried in the 2021 trial’s raw data. One subject developed a 66.7% rise in microcomedones under a blank pad with nothing on it. Another showed only a 37.5% rise under octyl palmitate, the positive control that plugged every other back in the study. The authors’ comment: “This depicts a subject variability.” They also report that isopropyl myristate, the classic positive control, “may not be a good positive control for comedogenicity test in human studies, particularly in Asian subjects having lower comedogenicity sensitivity than Caucasians.” The 2025 review adds that genetics contribute to adult acne and that “there is no guarantee that a product is noncomedogenic since reactions vary from person to person.”

One more problem sits on top of all five. The 2025 review notes that the ingredient-checking databases consumers rely on “are based on the original Kligman and Mills comedogenic ingredient list” and “are also not governed by scientific or regulatory standards.” That is why the same ingredient can carry a 0 on one site and a 3 on another. Nobody is refereeing.

What a real comedogenicity test looks like

Because most commercial articles never show you the method, here is the human protocol as run in the 2021 double-blind trial, which follows the Draelos and DiNardo design. Knowing this makes the “I used it for a week and didn’t break out” logic much easier to evaluate.

Three things stand out. First, even a formal test needs a full month under exaggerated conditions to produce a readable result. Second, the four finished creams in that trial contained lanolin, apricot kernel, avocado and sunflower lipids, ingredients that appear on rabbit charts with ratings from 0 to 4 depending on which site you read, and every one of them passed as non-comedogenic on human skin. Third, the negative control fell by 43%, which tells you that counting plugs on any given day is noisy. A single “before and after” on your own face is noisier still.

What “non-comedogenic” on a label legally means

Nothing specific. The FDA’s own Cosmetics Labeling Claims page states that “the law does not require cosmetic labeling to have FDA approval before cosmetic products go on the market, and FDA does not have a list of approved or accepted claims for cosmetics.” Claims must simply be “truthful and not misleading.” That page links to individual explainers for five loosely used terms: “alcohol free,” “cosmeceutical,” “cruelty free,” “hypoallergenic” and “organic.” Non-comedogenic is not among them. The 2025 JAAD Reviews paper fills the gap: “The United States Food and Drug Administration does not have a legal definition for the term ... Therefore, manufacturers can make noncomedogenic claims without regulation.”

If that sounds familiar, it is because the FDA says almost exactly the same thing about “hypoallergenic”: “The term means whatever a particular company wants it to mean.” Non-comedogenic is in the same category, a claim with market value and no shared test behind it. (Advertising claims, as opposed to label claims, fall to the Federal Trade Commission, which the FDA page also notes.)

So why does the American Academy of Dermatology still tell people with acne to look for it? Its advice for acne-prone skin is to “use only makeup, sunscreen, skin, and hair-care products that are labeled ‘non-comedogenic’ or ‘won’t clog pores,’” and its pore-care page goes further: “If you don’t see one of these terms, don’t use the product.” The two positions are not really in conflict. The AAD’s own wording is that such products “don’t cause breakouts in most people”, a statement about intent and probability, not a guarantee, and it immediately adds that “even non-comedogenic makeup can cause acne if you sleep in it.” Read the label as a signal that the brand thought about the question, then verify on your own skin.

Where plant lipids sit in all of this

This is the part that matters if you use, or are wary of, face oils and lipid serums. Rabbit charts are unkind to whole plant lipids: the 2025 review’s table lists coconut, cocoa butter and wheat germ at 4–5, and the review notes that in the 1970s “rich natural oils and certain emollients were frequent offenders.” Many people extrapolate from that to “oils clog pores.” The human data do not support the extrapolation.

Two findings are worth knowing. The first is the 2021 trial above: finished creams built on sunflower, avocado and apricot kernel lipids plus lanolin passed a formal human test. The second is older and more specific. In a double-blind, placebo-controlled cross-over trial published in Clinical and Experimental Dermatology in 1998, Letawe, Boone and Piérard applied linoleic acid, the main fatty acid in many seed lipids, to the skin of people with mild acne and measured their microcomedones by digital image analysis of cyanoacrylate biopsies. They reported “an almost 25% reduction in their overall size ... over a 1-month treatment period,” with no change at placebo sites, and concluded that “topical linoleic acid might play a role as a comedolytic agent in acne-prone patients.” It is one small study, and it tested a single fatty acid rather than a whole plant lipid, so treat it as early evidence rather than proof. But it points in the opposite direction from the charts.

What seems to matter is not “oil or not oil” but which fatty acids dominate. A 2018 review of plant lipids on skin by Lin, Zhong and Santiago in the International Journal of Molecular Sciences reports that linoleic-rich sunflower seed lipid preserved stratum corneum integrity and improved hydration, whereas continuous application of oleic-rich lipids disrupted the barrier. The same review gives the fatty-acid make-up of several lipids that appear in botanical serums:

The consumer charts give each of these a number, and, as the 2025 review notes, the number changes from site to site because nobody governs the lists. Not one of those numbers came from a finished-product human test. The fatty-acid column is verifiable chemistry. The rating column is folklore with a citation trail that stops in a rabbit’s ear.

One honest caveat belongs here. If you have active acne, the AAD’s guidance is to choose products labelled “oil-free,” “won’t clog pores” or “non-comedogenic,” and a 100% lipid serum is by definition not oil-free. Products like SD7 are designed for people whose concern is the look of fine lines, texture and dullness in mature skin, not for acne, and nothing here should be read as advice to put a lipid serum on a breakout. If acne is your problem, see a dermatologist, and note that the AAD says even proper acne treatment takes six to eight weeks to show improvement.

The 4-to-8-week single-variable trial

Since neither a chart nor a label can tell you what a finished product does on your face, here is a home version of the logic the human assays use. It is not a clinical test, and it will not detect microcomedones you cannot see. What it does is stop you blaming or clearing the wrong product.

1. Change one thing. Introduce the new product and nothing else. If you also switch cleanser, sunscreen or hair product in the same fortnight, you have no way to attribute a result. The AAD notes that hair-care products cause breakouts too, so hold those constant.
2. Take a baseline. Photograph your face in the same light, same time of day, no makeup, on day one. Count or mark any small bumps on cheeks, chin and forehead, the classic acne cosmetica zones per the AAD.
3. Use it as directed, unoccluded. The formal assay exaggerates exposure with a saturated pad under tape for 48–72 hours. Real use is a thin layer, open to air. That is why a home trial needs more calendar time than the lab’s four weeks, not less.
4. Do not sleep in makeup during the trial. The AAD’s line is unambiguous: even non-comedogenic makeup can cause acne if you sleep in it. A trial confounded by that habit tells you about the habit.
5. Check at week 4, then week 8. Four weeks is the formal assay length and the earliest point a fair verdict is possible. But the AAD says acne cosmetica “can take anywhere from a few days to 6 months for blemishes to appear,” so a clean week 4 is encouraging, not conclusive. Repeat the photo at week 8.
6. Know what a positive looks like. Per the AAD, acne cosmetica shows as “many tiny bumps” on the cheeks, chin or forehead, often whiteheads that rise slightly above the skin, appearing where the product goes. A single cystic spot on your jawline in week two is far more likely to be hormonal timing than the serum.
7. Separate clogging from irritation. Stinging within minutes, redness the same day, or itch and scale after a few days are irritant or allergic reactions, not comedones. They need a different decision tree, which we cover in Why Does My Serum Sting?. Note DermNet’s caveat that a test patch on thicker skin such as the forearm can be falsely reassuring for the face.
8. If it is a positive, stop, and wait. The AAD says acne cosmetica “will often clear when you stop using” the product that clogs your pores, and that even with over-the-counter treatment it can take four to eight weeks to see improvement. Do not restart until the baseline is back; then, if you want certainty, re-challenge once.

The point of this protocol is not to be paranoid. Most products, as the 2025 review says, “are generally acne-safe.” The point is that when something does go wrong, one careful trial beats fifty screenshots of a chart.

How to use the charts without being misled by them

The scale is not useless. Used narrowly, it is a decent early-warning system. Three rules keep it honest.

Flag the strong offenders, high on the list. A handful of ingredients scored 4–5 in rabbits and plugged human follicles in the assays above: isopropyl myristate, octyl palmitate (ethylhexyl palmitate) and acetylated lanolin. US regulation 21 CFR 701.3 requires ingredients to be listed in descending order of predominance down to 1%, after which order carries no concentration information, so a 4–5 ingredient in the first five lines of a leave-on product deserves attention. The same ingredient in position 20 probably does not. Even here, the 2025 review notes that isopropyl myristate appears in some tretinoin acne creams, and that in cleansers “often marketed as noncomedogenic,” so do not assume a brand has checked.

Ignore the difference between a 0, a 1 and a 2. Those gradations were never validated against human faces, and they change from site to site. Treat everything under 3 as “no signal.”

Never rate a product by its worst ingredient. That is the exact assumption Draelos and DiNardo tested and found wanting. A finished formula with one rated-3 ingredient at 1% is not a rated-3 product. Only a finished-product test, formal or the home version above, can tell you what it is.

Sources

1. Starzyk T, Aust N, Schur N, Miller R. “Comedogenicity in cosmeceuticals: A review of clinical relevance, regulatory gaps, and future directions.” JAAD Reviews 2025;6:78–83. Open access. doi:10.1016/j.jdrv.2025.09.002
2. Draelos ZD, DiNardo JC. “A re-evaluation of the comedogenicity concept.” J Am Acad Dermatol 2006;54(3):507–512. doi:10.1016/j.jaad.2005.11.1058
3. Waranuch N, Wisutthathum S, Tuanthai S, et al. “Safety assessment on comedogenicity of dermatological products containing d-alpha tocopheryl acetate in Asian subjects: A double-blind randomized controlled trial.” Contemp Clin Trials Commun 2021;23:100834. Open access. doi:10.1016/j.conctc.2021.100834
4. Letawe C, Boone M, Piérard GE. “Digital image analysis of the effect of topically applied linoleic acid on acne microcomedones.” Clin Exp Dermatol 1998;23(2):56–58. PubMed 9692305
5. Lin TK, Zhong L, Santiago JL. “Anti-Inflammatory and Skin Barrier Repair Effects of Topical Application of Some Plant Oils.” Int J Mol Sci 2018;19(1):70. doi:10.3390/ijms19010070
6. American Academy of Dermatology. “10 skin care habits that can worsen acne.” aad.org
7. American Academy of Dermatology. “I have acne! Is it okay to wear makeup?” aad.org
8. American Academy of Dermatology. “What can treat large facial pores?” aad.org
9. U.S. Food and Drug Administration. “Cosmetics Labeling Claims.” fda.gov
10. U.S. Food and Drug Administration. “‘Hypoallergenic’ Cosmetics.” fda.gov
11. DermNet. “Open application test.” dermnetnz.org
12. Electronic Code of Federal Regulations. 21 CFR §701.3, “Designation of ingredients.” ecfr.gov
13. American Academy of Dermatology. “Dermatologists’ top tips for relieving dry skin.” aad.org
14. Boucetta et al. Randomised study of cosmetic argan and skin elasticity in 60 postmenopausal women. Clin Interv Aging 2015. PubMed 25673976
15. Dhaliwal et al. Randomised controlled comparison of topical bakuchiol and retinol (n=44). Br J Dermatol 2019. PubMed 29947134

This article is for general information about cosmetic products and skin appearance. It is not medical advice. Cosmetic products support the appearance of skin and are not medicines. If you have persistent breakouts, a rash, or a reaction to any product, consult a dermatologist or physician.