For years, skincare has been simplified into a number.
An ingredient is given a score from 0 to 5.
0 means “non-comedogenic”
5 means “highly comedogenic”
It sounds scientific. It feels precise. It gives people a sense of control.
But when you look at where this system came from, and how skin actually works, the entire idea starts to break down.
Where Did These Ratings Come From?
Most comedogenic ratings trace back to research done in the 1960s–1980s, primarily by dermatologist Dr. Albert Kligman, one of the pioneers in acne research.
In these experiments, ingredients were applied to rabbit ears to observe whether they caused comedones (blocked follicles).
This method became known as the rabbit ear assay.
The issue is simple:
Rabbit skin is far more reactive than human skin.
It produces comedones more easily and responds differently to irritation. So ingredients that appeared highly comedogenic in rabbits often do not behave the same way on human skin.
Even Kligman himself acknowledged limitations in translating these findings directly to real-world use.
What Happens When We Test On Human Skin?
When researchers began testing ingredients on actual people, the results became far less predictable.
A key study by Fulton et al. (1989) evaluated commonly used cosmetic ingredients under real-use conditions. The findings showed that:
• Some ingredients classified as “highly comedogenic” did not consistently produce comedones in humans
• Results varied depending on formulation and concentration
• Individual skin response played a major role
In other words, the same ingredient could behave very differently depending on context.
This alone challenges the idea that a fixed “rating” can reliably predict outcomes.
The biggest flaw: ingredients aren’t used in isolation
Comedogenic ratings are based on testing single ingredients at high concentrations.
But real skincare doesn’t work that way.
In actual formulations:
• Ingredients are diluted
• They are combined with other compounds
• Their absorption and behavior are altered
An ingredient that may clog pores at 100% concentration could be completely non-problematic in a balanced formula.
This is well understood in formulation science.
The structure of the formula, not just the ingredient, determines how it interacts with the skin.
Skin Isn't Standardized
Another major issue with comedogenic ratings is the assumption that all skin behaves the same. It doesn’t.
Acne and clogged pores are influenced by multiple internal and external factors, including:
• Hormonal fluctuations (androgen activity, sebum production)
• Sebaceous gland activity
• Bacterial colonization (Cutibacterium acnes)
• Inflammation and immune response
• Skin barrier integrity
• Diet
This is why two people can use the exact same product:
• One breaks out
• The other sees improvement
Dermatology literature consistently describes acne as a multifactorial condition, not something caused by a single ingredient alone.
Where Does Tallow Fit Into This?
Tallow is often labeled around a 2 out of 5, which is “low to moderately low comedogenic potential.”
But that number is not based on direct modern testing of tallow on human skin. It’s inferred from its fatty acid profile, mainly its content of oleic, palmitic, and stearic acids.
Oleic acid, in particular, has been associated with higher comedogenic potential in older models, which is why tallow often gets grouped into a moderate range.
However, this is where the rating system becomes misleading.
These classifications come from:
• Isolated fatty acid testing
• High concentration models
• Animal-based studies
Not from real-world use of whole, minimally processed tallow in finished formulations.
Tallow is structurally different from many plant oils. Its fatty acid composition is relatively similar to human sebum, and it is highly stable due to its low polyunsaturated fat content.
This means its behavior on skin is influenced by more than just one fatty acid.
In practice, tallow tends to be well tolerated by some people, especially those with dry or compromised skin, while others may find it too heavy depending on their skin type and usage.
Like any fat, it is context-dependent.
This variability highlights the core issue with comedogenic ratings:
They cannot reliably predict how a real ingredient, used in a real formulation, will behave on your skin.
The Problem With Oversimplification
The comedogenic scale tries to compress all of this complexity into a number.
But in doing so, it ignores:
• Dose (how much of an ingredient is used)
• Delivery (how it’s formulated)
• Biology (how your skin behaves)
Even within scientific studies, results are inconsistent across different testing conditions.
This is why many dermatologists today do not rely heavily on comedogenic ratings when evaluating products.
What Actually Matters More
If the goal is clear, healthy skin, a better approach is to focus on:
1. Overall formulation quality
Simple, well-balanced formulations tend to be more predictable and better tolerated.
2. Skin barrier health
When the barrier is compromised, skin becomes more reactive and increases the likelihood of breakouts regardless of ingredient choice.
3. Individual response
Your skin is the only real testing ground that matters.
A More Practical Way To Think About It
Instead of asking:
“Is this ingredient comedogenic?”
A better question is:
“How does this product behave on my skin over time?”
Because no rating system can fully predict:
• your hormonal environment
• your skin microbiome
• your tolerance
The Bottom Line
Comedogenic ratings are not useless, but they are often misunderstood and over-relied on.
They are based on:
• outdated testing models
• inconsistent human data
• simplified assumptions about skin
They can offer a rough reference point, but they should not be treated as rules.
Skincare is more nuanced than a number on a chart.
References
• Kligman, A.M. (1972). An evaluation of the comedogenicity of cosmetic ingredients and vehicles. Journal of the Society of Cosmetic Chemists.
• Fulton, J.E. (1989). Comedogenicity and irritancy of commonly used ingredients in skin care products. Journal of the Society of Cosmetic Chemists.
• Draelos, Z.D. (2006). The effect of comedogenic ingredients on acne. Dermatologic Therapy.
• Webster, G.F. (2002). Acne vulgaris. BMJ.
• Gollnick, H. et al. (2003). Management of acne: a report from a Global Alliance. Journal of the American Academy of Dermatology.
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