CosDNA Review: Reading Acne and Irritant Ratings Correctly

CosDNA is an ingredient database that shows each ingredient in a product with its function and an acne and irritant rating from zero to five, where lower means less likely to clog pores or irritate. It's useful for spotting heavy pore-cloggers near the top of a list. The comedogenic scale itself was built on rabbit-ear tests of raw ingredients, so treat each number as an early warning.

Below we explain what each column means, where the acne numbers come from, why they can mislead acne-prone skin, and a step-by-step way to use the site. We make Pori, an app with its own ingredient scanner, so read our take with that in mind. CosDNA's site blocked our automated checks in October 2026, so we describe it from published coverage and from the research behind its numbers, and we couldn't confirm its newest features.

Is there a better alternative to CosDNA?

It depends on what you want from an ingredient check. If you want each ingredient judged against your own skin type, Pori is our pick, and yes, it's our app. You scan a barcode or photograph a label and each ingredient is flagged beneficial, use with caution or avoid for your skin type, using fixed rules over a curated list of about 250 INCI ingredients. The same app scores your skin from a selfie, so you can see whether a product change shows up over the following weeks. The scanner is part of Pro ($9.99 a week with a 3-day trial for eligible Apple IDs, or $49.99 a year, US prices as of October 2026), it's iPhone-only, and its barcode coverage of US products is thinner than the biggest databases.

CosDNA's strengths are different: it's a website you can use from any browser, and it puts acne and irritant numbers for a whole list on one screen. If you mainly want fungal-acne flags or a routine log, see our SkinCarisma review, and for a wider field, our list of INCIDecoder alternatives.

What do CosDNA's acne and irritant numbers mean?

The acne column estimates how likely an ingredient is to clog pores, and the irritant column estimates how likely it is to irritate skin; on both, 0 is the lowest risk and 5 the highest. A product page shows the full ingredient list as a table, one row per ingredient, with its function and these ratings, as Marie Claire described when it covered the site.

• Acne (comedogenic): how readily the ingredient produced clogged follicles (comedones) in testing.
• Irritant: how much surface irritation the ingredient caused in testing.
• Safety: a separate hazard index. Published guides describe its range differently (0 to 5 in one, 1 to 9 in another), but in each, a lower number means less concern.

An empty cell is best treated as unknown. A missing acne number doesn't tell you an ingredient was tested and passed.

Where do comedogenic ratings come from?

They come mostly from the rabbit-ear assay, an animal test that has been used since the mid-1950s to measure how much a substance thickens and plugs follicles. Dermatologists Kligman and Mills described the idea of "acne cosmetica" in 1972, linking certain cosmetic ingredients to closed comedones, and lists of ingredients to avoid grew out of that work.

The best-known ingredient list is James Fulton's 1989 survey in the Journal of the Society of Cosmetic Chemists. In his method, each ingredient was diluted to 10% in propylene glycol and 1 mL was spread on the inner ear of albino rabbits once a day, five days a week, for two weeks. Follicle plugging was measured under a micrometer and graded 0 to 5. Surface irritation was graded on a similar 0 to 5 scale, from no irritation up to scaling, redness and swelling, and, at 5, dead and sloughing skin.

The same numbers turn up across ingredient sites today. Fulton graded isopropyl myristate 5 for comedogenicity and 3 for irritancy, and INKEEDecoder (formerly INCIDecoder) currently lists it at irritancy 3 and comedogenicity 3 to 5. Here's how a few common ingredients scored in Fulton's table:

Source: Fulton, J Soc Cosmet Chem, 1989, Table I. CosDNA and other sites may show different numbers for the same ingredient when they draw on other studies.

Why can a CosDNA acne rating mislead you?

Because the test conditions are far from how you use a product. Four gaps matter most for breakouts.

1. The rabbit ear overreacts. Fulton himself called the model's main drawback its "extreme sensitivity": the rabbit ear develops plugs in two weeks, while similar reactions can take six months on human skin, and not everything that irritates the ear irritates people. When Mills and Kligman built a human test on the backs of volunteers, they found the rabbit model more sensitive than the human and judged weakly comedogenic substances probably safe, with the possible exception of acne-prone people. A 1982 review questioned whether the rabbit model correlated with experience in humans at all.
2. Raw ingredient, not your product. The ratings describe one ingredient at a fixed test strength. In a 2006 study, dermatologist Zoe Draelos and a co-author tested finished products on six people prone to comedones and concluded that finished products using comedogenic ingredients are not necessarily comedogenic.
3. No percentages. US labels list ingredients in descending order of predominance, but anything at 1% or less can appear in any order after that. A 4 near the end of a long list may be present in a trace amount, and CosDNA can't tell you how much is there.
4. Your skin is the real test. The American Academy of Dermatology notes that some products labeled non-comedogenic may still cause acne in a few people. The reverse also happens: a product with a flagged ingredient can suit you fine.

The irritant column has its own catch. In the source research it measured scaling and redness on rabbit skin after daily application, which is a different thing from the sting some people feel from fragrance or acids on the face.

How do you use CosDNA sensibly for acne-prone skin?

Use it to narrow down suspects, then let your skin decide. A practical routine:

1. Paste or search the full ingredient list, and check it against the box or the brand's site, since formulas change.
2. Look at the first five to ten ingredients first. Labels list ingredients from most to least above 1%, so a 4 or 5 there matters more than one in the last few lines.
3. Don't drop a product for a scattering of 1s and 2s. Fulton didn't treat a 0 or 1 as significant, and 2 to 3 was borderline.
4. Read the acne and irritant columns together. A product with low acne numbers but several high irritant numbers may still be a poor match for sensitive, breakout-prone skin.
5. Introduce one product at a time. The AAD says blemishes from makeup can take anywhere from a few days to 6 months to appear, so changing several things at once makes the culprit impossible to find. Our guide to patch testing skincare explains the steps.
6. Keep notes and photos. If you break out, write down the products you started in the weeks before. Then compare their lists on CosDNA for a shared high-rated ingredient. Our guide to breaking out after a new product covers how to tell a reaction from purging.

Is CosDNA accurate?

It's a reasonable record of how ingredients behaved in older tests, and a poor predictor of how a finished product will behave on your face. The numbers are only as good as the studies behind them, which are decades old and, for comedogenicity, largely from rabbits. Treat a high score as a reason to watch a product more closely, and a low score as no guarantee.

CosDNA also covers only part of the acne picture. It can't tell you whether bumps are acne at all. Small, uniform, itchy bumps on the chest, back or forehead can be Malassezia (fungal) folliculitis, which DermNet notes shows no comedones and responds to antifungal treatment, not to cutting comedogenic ingredients. See our explainer on fungal acne vs regular acne.

When should you see a dermatologist instead?

See a dermatologist if your acne includes deep, painful cysts or nodules, if it doesn't improve with over-the-counter treatment, or if it's affecting how you feel. The AAD suggests giving an acne treatment at least 4 weeks, with improvement usually seen within 4 to 6 weeks and clearing taking two to three months or longer. No ingredient site can diagnose a skin condition or replace that visit.

The verdict

CosDNA is a fast way to scan an ingredient list for well-known pore-cloggers, and it's most useful when you're hunting for a pattern across products that broke you out. Its acne and irritant numbers are inherited from animal tests of raw ingredients, so they overstate risk for many people and say nothing about concentration. Use it to shortlist suspects, test products one at a time, and trust what your skin does over what the column says.