How reliable is the comedogenic scale?

One of the most intriguing topics of discussion in the beauty community today is comedogenicity of ingredients in makeup and skincare products. What is comedogenicity, do 100% comedogenic ingredients exist and how is it that a product that works great for all your friends doesn’t suit you is explained by our dear associate, Lucija Božičević.

Comedones are non-inflammatory forms of acne that develop in the pores next to the hair follicle. Other factors that play a role in comedone development are sebaceous glands (also located in the pores) and desquamation or shedding of the skin. When all physiological functions are working properly, the shed skin cells and the sebum secreted from the sebaceous gland are pushed from the pore to the surface of the skin. However, if the skin’s proper functioning is disrupted there is a high risk that these discarded parts of the skin will remain inside the clogged pore and become a comedone, like a plug inside the pore. When talking about comedones, it is important to differentiate between two types – open and closed. Open comedones are known as blackheads because they look like black spots. This type of comedone presents a far lesser problem than the closed type and can be easily resolved by facials. Their appearance can also be prevented by following a proper cleansing and skin care routine. Closed comedones are a heaven for the Propionibacterium acnesbacteria. Inside the closed comedone, helped by the lack of oxygen, these bacteria will break the sebum’s lipids into free fatty acids that have a pro-inflammatory effect and will lead to development of inflammatory acne.

Comedogenicity of a certain ingredient actually refers to the potential of the pore to clog if that specific ingredient is applied, in turn leading to the development of a comedone. It is important to stress that comedogenicity is a relative term for many reasons. The first is that a specific ingredient will not have the same comedogenicity potential for each person. It highly depends on their skin type. In general, persons with oily skin are much more prone to comedones, and if their skin is also sensitive, the potential for comedone development becomes significantly higher. That is why on that type of skin a certain ingredient may cause comedones and acne very quickly, but a person with non-sensitive and dry skin that doesn’t produce a lot of sebum won’t have any problems with the same ingredient. The second important thing for comedogenicity is the formulation of the product. All ingredients are not equally comedogenic and the composition of the product may affect to what degree the product itself will be comedogenic. For example if a formulation includes an average comedogenic ingredient in a high concentration, paired with other comedogenic ingredients, it becomes much more unsafe for use. The same ingredient, in a formulation in which it is the only comedogenic ingredient and its concentration is low (it’s found towards the bottom of the ingredient list), will cause problems only for the most sensitive skin.

In determining the comedogenicity of ingredients, the golden standard was first the rabbit ear test. In earlier times such tests were used for determining the harmful effects of topical application of certain chemicals and then later began to be applied for testing cosmetic products and raw materials. Today comedogenicity is more and more often tested using a patch test on human skin.

We have already mentioned that the comedogenic properties of an ingredient are highly relative. After having explained the reasoning behind this claim, we now must question whether proper testing is actually even possible. Most of the ingredients that are considered comedogenic are considered as such from the very early days and the first comedogenicity tests Fulton performed on rabbit ears. Fulton categorised raw materials as ranging between the numbers 0-5, with 0 standing for non-comedogenic and 5 meaning extremely comedogenic. However, online sources and ingredient lists don’t tell you how the raw material was extracted and processed before it was incorporated into the product. If the raw material was fractioned (separated into the low-molecular and high-molecular fraction), hydrogenated, refined or PEGylated (by addition of polyethylene glycol) its comedogenic potential may be significantly reduced.

A list of ingredients a product must not contain in order to be categorised as non-comedogenic does not exist. Therefore, before we list certain individual or groups of raw materials considered comedogenic, it is necessary to point out that this description of raw materials has not been taken from any specific data base based on thorough scientific research or confirmed by some kind of regulatory agency. The most commonly stated comedogenic ingredients are various oils derived from natural sources, especially coconut oil and castor oil and coconut, cocoa and shea butter. These raw materials are extremely lipophilic and they act as occlusive agents, which is why they are assigned a high comedogenicity potential. Lanolin is considered a highly comedogenic ingredient but its acetylated and PEGylated variations have milder comedogenic properties, while jojoba oil and olive oil are categorised as moderately comedogenic ingredients so their negative effects will depend more on skin type and concentration in the product. Argan, macadamia and borage seed oil have not been sufficiently tested and their comedogenic potential cannot be established with certainty.

Certain derivatives of isopropyl alcohol and fatty acids (isopropyl myristate, isopropyl lanolate) are also comedogenic but one must keep in mind that their concentration in a product may vary greatly depending on their function. Also certain fatty acids such as lauric or eicozanoic acid may cause acne in case of sensitive skin. It is a common misconception that polysorbate emulsifiers (polysorbat 20, polysorbat 80) are comedogenic which, at least according to the most comprehensive research study carried out on comedogenicity of ingredients to date, is not true.

Comedogenicity of tocopherol (vitamin E) as well as Vitamin A and Vitamin D, most often found in lipophilic vitamins present in cosmetic products, highly depends on the derivative present in the product. This list could go on and on, but after having mentioned some of the most commonly cited “culprits”, it will suffice to say that an entire table was put together during the already mentioned most comprehensive study carried out on comedogenicity and can be found in the paper cited as the first reference used for this article.

Since information is very easily accessible to everyone today, there are many concerns and misconceptions about the application of a great number of products. This article has hopefully shed some light on the fact that comedogenicity is a very complex and insufficiently adequately researched problem. It is important to remember that each raw material and each product will not have the same effect on the skin of every individual, but depends on its type and level of sensitivity. It is recommended that persons with sensitive and oily skin prone to acne definitely check ingredient lists to see if they include comedogenic ingredients, at the same time having in mind that many of the online tools available for monitoring comedogenicity today are in reality just guidelines and in no way a concrete or 100% safe and reliable source. Until more concrete methods for determining comedogenicity are discovered, the only option is to choose products in an informed way.

REFERENCES:

  1. Fulton JE. Comedogenicity and irritancy of commonly used ingredients in skin care products. J. Soc. Cosmet. Chem., 1989, 40, 321-333
  2. Fulton JE et al. Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear. J Am Acad of Dermatol, 1984, 10, 96–105
  3. Draelos Z, J DiNardo J. A re-evaluation of the comedogenicity concept, J Am Acad Dermatol, 2006, 54, 507–512

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