Comedogenicity—A Complicated Conversation

Comedogenicity in cosmetic products has been studied for decades, but it has been a particularly hot topic the last few years. Clients and skin care professionals alike search through ingredient labels looking for terms such as “noncomedogenic” or “nonclogging,” hoping it will do no harm to acne-prone skin. But what does this term really mean and does it have validity? A closer analysis reveals that comedogenicity is a complicated and highly debated issue.

The process of clogging

Simply put, a comedogenic ingredient means that it clogs pores. It does so by increasing follicular hyperkeratosis—an increased production of keratin in hair follicles. Over time, this leads to clogged follicles and comedones. This doesn’t always happen quickly, and it can take months of using a comedogenic product before clogging is noticeable. Individual skin chemistry can determine the extent of an ingredient’s comedogencity, so it is highly variable between people. One client may have no reaction, while another may have excessively clogged pores in a few weeks. Even ingredients that are not typically comedogenic can become so by a person’s own unique skin enzymes. Human sebum is naturally comedogenic, so even if clients who are prone to clogging avoid all likely comedogenic products, they are not necessarily guaranteed protection against comedones. If this is the case, how do skin care professionals know if ingredients are playing a role in their clients’ clogged or acne-prone skin?

Comedogenicity testing

Although there is no definitive way to test for comedogenicity, the rabbit ear test has long been the gold standard. This test was originally used to assess the dangers of industrial chemicals in the 1950s and then entered the world of cosmetics in the 1970s. Rabbit ears were found to be more sensitive than human skin and also responded much more quickly to comedogenic ingredients. Follicular hyperkeratosis could be seen in a matter a weeks versus months.

Albert Kligman, MD, PhD, and James Fulton, MD, are known for pioneering the use of rabbit ears in cosmetic testing, and the term “acne cosmetica”—acne caused by the use of cosmetics with comedogenic ingredients—was coined at this time. Cosmetic rabbit ear testing was done by applying ingredients to the inner ear of rabbits, and follicular keratosis was analyzed both visually and microscopically after a few weeks. The first comedogenic lists created were broken into 12 ingredient categories: lanolins; fatty acids; alcohols and sugars; waxes; thickeners; oils; pigments; silicones; sterols; vitamins and herbs; preservatives; and miscellaneous ingredients. Testing results ranked ingredients from grade 0 to grade 5, with 5 being the most comedogenic. Ingredients ranked 4–5 resulted in an extensive increase in follicular keratosis and the presence of large comedones throughout the ear. Ingredients ranked 2–3 resulted in a moderate increase in follicular keratosis. Ingredients ranked 0–1 had no significant increase. Ingredients ranked 4–5 had reproducible results and were considered comedogenic ingredients. Ingredients ranked 0–1 were not considered significant and were considered noncomedogenic. Kligman and Fulton concluded that ingredients with higher numbers were to be avoided by those who had oily or acne-prone skin.

Today, comedogenic testing is also done on human subjects. This is particularly important, because animal testing is losing favor with consumers. These tests are often done in third-party labs, and each lab performs the test differently. Generally, 10–30 subjects receive patch applications that are tested against a positive control of a known comedogenic ingredient and an untreated site as a negative control. Sites are often chosen on the back; however, this varies by lab. At the end of the testing period, a surface biopsy is conducted, and the cells are then analyzed under magnification. Testing commonly runs for a time period of 4–8 weeks. Testing parameters can also be customized for the manufacturer.

Validity of comedogenicity claims

The primary issue when it comes to determining whether or not an ingredient is comedogenic is that there is no definitive list of comedogenic ingredients. Although there are several lists that can be found in published research and on various online websites, many lack actual testing of commonly used ingredients, which casts doubt on the validity of the list. Some lists label an ingredient as comedogenic, while another list labels that same ingredient as noncomedogenic. Several current studies even call into question the hallmark rabbit ear test, noting the absence of scientific correlation with human experience. Even later rabbit ear studies by Fulton resulted in some ingredients dramatically changing their comedognicity grade. Testing on human subjects is questioned, as well. Some say skin tested on the back is not accurate, because it will not respond similarly to facial skin and the duration of the testing is not long enough.

Discrepancies in comedogenic lists are based on several factors. First, depending upon the ingredient, concentration of that ingredient within the formula is important. A formula is not just a sum of its parts—ingredient combinations can turn a comedogenic ingredient into a noncomedogenic ingredient and vice versa. Secondly, the method in which an ingredient is extracted and processed plays a role. Whether an ingredient was refined, hydrogenated or fractionated can dramatically change its comedogenicity ranking. Third, the source of the raw material can affect its rating. Unfortunately, these variables cannot be easily determined by reading an ingredient label.

U.S. Food and Drug Administration (FDA) guidelines further complicate the issue. The FDA defines a comedogenic ingredient as one that is known to clog pores. However, the FDA does not define a list of ingredients that are excluded for a product to use the term “noncomedogenic.” So ultimately, any company can make the claim that its product is noncomedogenic and still fall within FDA guidelines. In addition, there is no standardized testing and are no watchdog groups to catch misuse of the claim. Even if the industry attempted standardization, it would be an extremely difficult and costly endeavor.

To date, third-party comedogenic testing of a complete formula on human skin is the best way to know whether or not a product is comedogenic, and it is also the only way to legally substantiate claims such as “noncomedogenic,” “unclogs pores” or “reduces the appearance of blackheads.” However, third-party comedogenic testing is expensive and, because there is little-to-no regulation over the use of the term, very few cosmetic companies take that extra step. This is particularly troublesome with new ingredients that have no historic rabbit ear comedogenic studies behind them. Skin care clients are left scouring literature in an attempt to find a study that tested that ingredient or simply search for anecdotal evidence.

Comedogenic ingredient lists can be used as guidelines; however, it should be kept in mind that only some ingredients—in all of their forms—have repeatedly shown comedogencity in scientific studies. Table 1 contains ingredients that have been shown to be highly comedogenic. Table 2 on lists ingredients that are often mislabeled as comedogenic, but are actually noncomedogenic. In order to avoid ingredients that are debated, the lists are not all-inclusive, but are an abbreviated consensus among several other well-known lists.

What estheticians can do

Although comedogenicity is not an exact science, there are steps that skin care professionals can take to help direct their clients to appropriate product choices.

  • Educate clients on the theory of comedogencity and explain that, although they may love a particular product, if it contains comedogenic ingredients, it may not be the best for their skin if it is acne-prone.
  • Instruct clients to bring along their products to their next appointment and examine the ingredient labels. Note that many companies have the ingredient label on the outer package and not directly on the bottle, so you may need to research the full ingredient deck online or request it from the manufacturer.
  • Be sure you know ingredients well. Similar sounding ingredients are not the same. Isocetyl alcohol is not the same as isopropyl alcohol; steareth-2 is not the same at steareth-10; caproic acid is not the same as capric acid; and squalane is not the same as squalene. Keep a list handy.
  • Keep in mind that comedogenic ingredients fall across all categories, from emulsifiers to thickeners, surfactants, waxes and oils. “Oil-free,” for example, does not mean it is noncomedogenic. Although several oils are comedogenic, many are not, and some are actually good for acne-prone skin.
  • Seek out products that conduct independent third-party comedogenic testing by reputable labs. This may not be apparent from the label—reach out to the manufacturers directly if this is the case. Don’t be afraid to ask for their study results. If third-party testing is not available, request the information from which they concluded their product to be noncomedogenic.

Err on the side of caution

A product that has a comedogenic ingredient is not a bad product—it may just not be the best choice for someone that is clog- or acne-prone. It very well may be a fantastic product for those with drier skin types and smaller pores.

Although every client’s skin will respond differently, it is best to avoid known comedogenic ingredients for skin that is acne-prone. With so many choices on the market today, it is easy to err on the side of caution.

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GENERAL REFERENCES

Z Draelos and J DiNardo, A re-evaluation of the comedogenicity concept, J Am Acad Dermatol 54 3 507–12 (2006)

J Fulton, Comedogenicity and irritancy of commonly used ingredients in skin care products, J Soc Cosmet Chem 40 321–33 (1989)

J Fulton, S Bradley, et. al., Non-comedogenic cosmetics, Cutis 17 344–51 (1976)

J Fulton, S Pay, et. al., Comedogenicity of current therapeutic products, cosmetics, and ingredients in the rabbit ear, J Am Acad of Dermatol 10 96–105 (1984)

A Kligman and O Mills, Acne cosmetics, Arch Dermatol 106 843–850 (1972)

A Kligman and T Kwong, An improved rabbit ear model for assessing comedogenic substance, Br J Dermatol 100 6 699–702 (1979)

O Mills and A Kligman, A human model for assessing comedogenic substances, Arch Dermatol 118 11 903–5 (1982)

W Morris and S Kwan, Use of the rabbit ear model in evaluating the comedogenic potential of cosmetic ingredients, J Soc of Cosmet Chem 34 215–25 (1983)

Michelle Calvarese, PhD, is a licensed esthetician, as well as president and CFO of dermaTRUTH and founder of Truth Skin Care Esthetics Clinic. She can be contacted at mcalvarese@dermatruth.com.