Complete Guide to Comedogenic Ingredients: Ratings, Oils, and What the Scale Really Means

"Non-comedogenic" is one of the most common claims on skincare products marketed to people with acne-prone skin. Yet there is no regulatory legal definition for the term in the US, EU, or most other markets — any brand can print it on any product. Understanding what comedogenicity ratings actually measure, how they were developed, and what their real-world limitations are is essential for making sense of ingredient lists without being misled by marketing language.

What Is Comedogenicity?

A comedo (plural: comedones) is a plugged hair follicle. Blackheads (open comedones) and whiteheads (closed comedones) are both types of comedones and represent the earliest stage of acne vulgaris. Comedogenicity refers to an ingredient's or product's tendency to promote comedo formation by contributing to follicular plugging.

The mechanism by which an ingredient might cause comedone formation involves several potential pathways: direct physical occlusion of the follicular opening, chemical stimulation of increased sebum production, alteration of the desquamation (skin cell shedding) process within the follicle, or interaction with the Cutibacterium acnes (formerly Propionibacterium acnes) bacterial environment. Not all of these are equally well-established.

The Kligman-Mills Comedogenic Scale (1972)

The foundational work for modern comedogenic rating systems was published by Albert M. Kligman and Otto H. Mills in their 1972 paper "Acne cosmetica" in the Archives of Dermatology. They developed a methodology for rating ingredients by applying them to the inner surface of rabbit ears and observing follicular changes histologically after several weeks. The ratings produced a scale from 0 to 5:

Rating	Interpretation	Example Ingredients
0	Non-comedogenic	Glycerin, niacinamide, hyaluronic acid / sodium hyaluronate, salicylic acid
1	Slightly comedogenic	Dimethicone, squalane, most silicones
2	Mildly comedogenic	Sunflower oil, olive oil, safflower oil (refined)
3	Moderately comedogenic	Lauric acid, myristic acid, some mineral oils (certain grades)
4	Fairly comedogenic	Coconut oil (~4/5), some grades of cocoa butter, linseed oil
5	Highly comedogenic	Isopropyl myristate, wheat germ oil, acetylated lanolin

Critical Limitation: The Rabbit Ear Model

The Kligman-Mills scale was derived from a rabbit ear (inner pinna) model, not from human skin. Rabbit ear skin has distinct properties from human facial skin: it contains densely packed follicles that respond differently to topical compounds, has different barrier function characteristics, and is generally considered more susceptible to comedone formation than human skin.

A pivotal 2006 paper by Draelos and DiNardo in the Journal of the American Academy of Dermatology revisited the comedogenicity concept, concluding that "the rabbit ear assay is not predictive of comedogenicity in humans" and that the correlation between rabbit ear ratings and human acne outcomes is weak. The authors recommended that comedogenicity assessments for finished products use human back or arm models instead.

"The rabbit ear assay has poor predictive validity for human comedogenicity. Finished product testing on human subjects at in-use concentrations provides a more clinically relevant assessment." — Draelos & DiNardo, JAAD 2006

This does not make the scale useless — it remains a reasonable screening tool for formulation decisions and is widely used in the industry as a starting point. But it means that an ingredient rated 4/5 in the rabbit ear model may not produce comedones in every person who applies it to their face, and an ingredient rated 0 is not guaranteed to be non-comedogenic for everyone.

High-Comedogenic Ingredients (Ratings 4–5)

Isopropyl Myristate — Rating 5/5

Isopropyl myristate (IPM) is an ester of isopropyl alcohol and myristic acid, used extensively as an emollient, penetration enhancer, and texture-improver in cosmetics. It gives products a smooth, non-greasy, silky feel. The Cosmetic Ingredient Review (CIR) panel has confirmed its safety for topical use, but its comedogenic rating of 5/5 makes it one of the most frequently cited problematic ingredients for acne-prone skin.

IPM's comedogenicity appears related to its penetration-enhancing properties — it can disrupt follicular epithelium and increase penetration of other materials into the follicle. It is found in foundations, moisturizers, lip products, and sunscreens. Related esters such as isopropyl isostearate, isopropyl palmitate, and myristyl myristate also carry high comedogenic ratings (3–5).

Wheat Germ Oil — Rating 5/5

Wheat germ oil is rich in linoleic acid (~55%), oleic acid (~17%), and palmitic acid (~16%), with a high vitamin E (tocopherol) content. Despite these nutritionally appealing properties, its comedogenic rating is 5/5 in the rabbit ear model. The specific mechanism is not fully established, but the combination of high-molecular-weight triglycerides and its particular fatty acid profile may contribute to follicular occlusion. Wheat germ oil is less commonly found in mainstream facial cosmetics for this reason.

Coconut Oil — Rating 4/5

Coconut oil's predominant fatty acid is lauric acid (~48%), followed by myristic acid (~18%) and palmitic acid (~9%). Lauric acid has been shown to have antimicrobial activity against C. acnes in vitro — an apparent paradox for a comedogenic ingredient. The antimicrobial effect may not outweigh the follicular occlusion promoted by the dense saturated fatty acid content, particularly in people already prone to acne.

Coconut oil's comedogenicity rating is consistently reported at 4/5. Its use in body care or hair treatments is generally less problematic because the follicular density and sebum production patterns of the body differ from facial skin. Many acne clinicians consider coconut oil a high-risk ingredient for patients with acne-prone facial skin.

Non-Comedogenic or Low-Comedogenic Ingredients (Ratings 0–1)

Glycerin — Rating 0/5

Glycerin (glycerol) is one of the most widely used humectants in skincare, functioning by drawing water from deeper skin layers toward the surface and from the environment into the skin. It has a comedogenic rating of 0. Its mechanism of action — water-binding rather than lipid-filling — means it does not contribute to the oxidized lipid environment in follicles that promotes comedone formation. Numerous studies, including a detailed analysis by Fluhr, Darlenski, and Surber (2008), have confirmed glycerin's role in improving skin hydration without disrupting the follicular environment.

Niacinamide — Rating 0/5

Niacinamide (vitamin B3) is non-comedogenic and has evidence suggesting it may actually help reduce sebum production and improve acne outcomes. A 1995 clinical study by Shalita et al. found topical 4% niacinamide comparable to 1% clindamycin gel for inflammatory acne. Its anti-inflammatory properties, sebum-regulating effects, and barrier-strengthening action make it a frequently recommended ingredient for acne-prone skin. Comedogenic rating: 0/5.

Hyaluronic Acid / Sodium Hyaluronate — Rating 0/5

Hyaluronic acid is a naturally occurring glycosaminoglycan that functions as a humectant. Its high molecular weight (1,000–1,800 kDa for standard forms; lower-MW versions penetrate more deeply) means it sits primarily on the skin surface where it binds water. Sodium hyaluronate (the sodium salt form, which is more stable and water-soluble) is the INCI name most commonly found on ingredient lists. Both forms have a comedogenic rating of 0. They are among the most universally tolerated skincare actives.

Salicylic Acid — Rating 0/5

Salicylic acid is a beta-hydroxy acid (BHA) that is both non-comedogenic (rating 0/5) and actively comedolytic — it helps dissolve the intercellular cement that binds cells within the follicular canal, promoting their shedding and helping to clear existing comedones. It is oil-soluble, allowing it to penetrate the sebum-rich environment of hair follicles. The FDA classifies topical salicylic acid as an OTC acne treatment at concentrations of 0.5–2%.

Dimethicone — Rating 1/5

Dimethicone is a linear polydimethylsiloxane polymer used as an emollient, film former, and skin protectant. Despite its occlusive feel, dimethicone's large molecular structure prevents it from penetrating follicular openings, giving it a comedogenic rating of approximately 1/5 — essentially non-comedogenic for practical purposes. It is frequently used in formulations specifically designed for sensitive or acne-prone skin as a skin-smoothing agent with low irritation potential.

Common Misconceptions

Misconception 1: "All Oils Are Comedogenic"

This is demonstrably false. Comedogenic ratings for common plant oils range across the entire scale. Squalane (derived from olives or sugarcane; not to be confused with squalene, the naturally occurring version) carries a comedogenic rating of 0–1. Rosehip oil is rated approximately 1. Hemp seed oil is approximately 0. Jojoba oil (technically a wax ester rather than a triglyceride oil) is rated 2. The fatty acid composition and molecular structure of each oil determines its comedogenic potential, not the fact that it is an oil.

Misconception 2: "Non-Comedogenic Products Cannot Cause Breakouts"

Acne involves multiple pathophysiological pathways. Comedone formation is one pathway, but inflammatory acne lesions also involve immune responses, bacterial colonization, and hormonal regulation of sebum production. A product that is formulated with genuinely low-comedogenicity ingredients can still theoretically exacerbate acne through irritation-induced inflammation or by containing fragrance, essential oils, or other potential sensitizers. The "non-comedogenic" claim speaks only to comedone formation potential, not to all acne-relevant properties.

Misconception 3: "The Rating Tells You About Finished Products"

Comedogenic ratings are assigned to individual ingredients in isolation, typically tested at high concentrations. In a finished formulation, ingredients interact. An emulsifier present at 1% in a formula alongside glycerin at 5% and niacinamide at 4% is a very different context from pure isopropyl myristate applied to a rabbit ear. Concentration effects are significant: the same fatty acid ester at 0.5% may behave very differently than at 20%.

Practical Formulation Guidance

For consumers with acne-prone skin reviewing ingredient lists, a practical tiered approach works better than ingredient-by-ingredient rating lookup:

• Tier 1 concern (scan for position in list): Isopropyl myristate, isopropyl palmitate, acetylated lanolin, coconut oil, wheat germ oil — if these appear in the first five ingredients of a leave-on product, they may be present at concentrations high enough to be relevant.
• Tier 2 (less concern in middle-list positions): Oleic-acid-rich oils like olive oil, argan oil, and avocado oil — moderate comedogenic ratings (2–3), but often used at lower concentrations in finished formulas.
• Low concern (can generally appear anywhere in list): Glycerin, niacinamide, sodium hyaluronate, dimethicone, salicylic acid, squalane — these have low comedogenic ratings and strong tolerability records.

Use our Ingredient Analyzer to check comedogenic ratings and regulatory status for your specific product's full INCI list.