How to assess the comedogenicity level of a skincare product?

The term "comedogenic" comes from the word "comedones" and refers to the ability of a cosmetic ingredient or a cosmetic product to block the sebaceous glands, which are responsible for the production of sebum. So-called "comedogenic" treatments tend to form a film on the skin's surface, quite similar to the naturally present hydrolipidic film. Indeed, this new occlusive layer helps to preserve the hydration of the epidermis and to limit insensible water loss (IWL). While this property is beneficial for dry skin, it is detrimental for combination to oily skin, whose sebum production is naturally high, and can lead to a dilation of the pores, microcysts, open (blackheads) or closed (whiteheads), or even spots, more or less red and swollen.

The comedogenicity, or occlusive potential, of a cosmetic ingredient is evaluated on a scale ranging from 0 to 5. An ingredient scoring 0 is considered non-comedogenic. From 1 to 2, it is deemed slightly comedogenic. A score above 3 indicates that the ingredient is comedogenic. This comedogenicity score is based, among other things, on its rate of penetration into the superficial layers of the skin and its vulnerability to oxidation.

Recruitment of volunteers.

To assess the comedogenicity of a skincare product, laboratories call upon a score of volunteers, aged between 18 to 65 years, who have no history of intolerance or allergy to a cosmetic product. Moreover, certain individuals are unable to participate in comedogenicity studies. These include pregnant women, people with a skin condition (acne, eczema, psoriasis, vitiligo...), those undergoing certain types of medication treatment recently (for example: change or cessation of hormonal treatment less than 5 weeks ago) and individuals with significant body hair, freckles, moles or a tattoo in the area of the experiment.

During the study.

For a period of 4 weeks, participants are required to apply the tested cosmetic product daily, adhering to specific conditions set by the laboratory. For instance, in the case of a moisturising cream, volunteers will be asked to apply it to their facial skin after it has been thoroughly cleaned and dried. After each use, participants are required to fill out an observation document detailing the condition of their skin and their sensations upon application (feelings of warmth, redness, itching, tingling, tightness...). Moreover, during the study period, the use of a product similar to the one being tested is not permitted. Volunteers are also asked not to alter their other hygiene and cosmetic habits.

After the study.

At the end of the four weeks, the volunteers return to the study centre where a clinical examination is conducted. The skin lesions are counted (comedones and microcysts) and the participant observation document is reviewed. The data is then processed electronically. The appearance or non-appearance of skin lesions during the study allows conclusions to be drawn about the occlusive potential of the product tested.

When one has skin prone to blemishes, it is crucial to be able to differentiate between comedogenic products and non-comedogenic skincare. To do this, you can start by checking the INCI list of the product to ensure it does not contain any comedogenic ingredients. However, it's worth noting that just because a comedogenic ingredient is present in a product, it doesn't necessarily mean that the product will cause comedones. Indeed, the comedogenicity of a skincare product also depends on the concentration of each ingredient. On an INCI list, ingredients are listed in descending order of their concentration in the product. Therefore, pay particular attention to the first 3 to 4 ingredients, those with the highest concentration. The table below groups together the most commonly used comedogenic ingredients in cosmetics.

• FULTON J.E. Comedogenicity and irritancy of commonly used ingredients in skincare products.Journal of the Society of Cosmetic Chemists (1989).

• DiNARDO J. C. & co. A reassessment of the comedogenicity concept. Journal of the American Academy of Dermatology (2006).