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 clog the sebaceous glands, which are responsible for sebum production. 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 dilation of the pores, microcysts, open (blackheads) or closed (whiteheads), or even pimples, 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 that scores a 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 rely on a group of about twenty volunteers, aged between 18 and 65 years, who have no history of intolerance or allergy to any cosmetic product. However, certain individuals are not eligible to participate in comedogenicity studies. These include pregnant women, individuals with a skin condition (acne, eczema, psoriasis, vitiligo...), those who have recently started certain types of medication (for example, those who have changed or stopped 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 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 moisturizing cream, volunteers will be asked to apply it to their facial skin that has been previously 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 change their other hygiene and cosmetic habits.

After the study.

At the end of the four weeks, the volunteers return to the study center 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 dealing with skin prone to blemishes, it's crucial to distinguish between comedogenic products and non-comedogenic skincare. To do this, you can start by checking the INCI list of the product to ensure it doesn't contain any comedogenic ingredients. However, it's important to note 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 includes 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. & al. A Reassessment of the Comedogenicity Concept. Journal of the American Academy of Dermatology (2006).