An ingredient is said to be comedogenic if, when applied to the skin, it blocks the pores and promotes the formation of an "occlusive" film. This prevents the normal evacuation of sebum and contributes to the appearance of blemishes: comedones. These take the form of blackheads or whiteheads. If you have acne-prone skin, applying a comedogenic ingredient is likely to exacerbate this skin infection.
To determine whether an oil is comedogenic or not, one can refer to its comedogenicity index, which ranges from 0 to 5. Theoretically, an ingredient with an index of 0 is considered non-comedogenic. From 1 to 2, it is deemed slightly comedogenic. An index above 3 indicates that the ingredient is comedogenic. This index is calculated to assess the occlusive potential of an ingredient.
However, it is crucial to note that the comedogenicity of an active ingredient does not necessarily lead to the emergence of skin imperfections. Similarly, the application of a skincare product containing a comedogenic ingredient does not always result in spots. This depends on its concentration in the product. Finally, the risk of developing imperfections after using a comedogenic ingredient also depends on the skin type of each individual.
Generally, it is preferable not to exceed a comedogenicity index of 2 for oily skin types. This type of skin is indeed more prone to blemishes and the appearance of spots. Normal to dry skin types, on the other hand, can tolerate oils with an index of up to 3.
Several factors influence the comedogenicity index of an ingredient, including:
Oxidation sensitivity and freshness : Over time, fatty acids or other compounds that make up an ingredient tend to oxidise and degrade. This phenomenon can potentially impair the quality of the skincare product and increase its comedogenicity index. Several factors can trigger this oxidation, such as exposure to air oxygen, light, heat, or even interactions with the container.
The quality of the oil : an oil derived from a cold-press extraction method retains the active substances present in the raw materials, such as fatty acids and vitamins. This process does not require chemical treatment, nor exposure to high temperature, which could destroy certain fatty acids in the vegetable oil and lead to the formation of new compounds, not necessarily beneficial for the skin.
The rate of penetration of vegetable oil into the epidermis : a thick and greasy oil is difficult for the skin to absorb, which can increase its occlusive nature. Conversely, the more the oil has a strong affinity with the skin, the easier it penetrates. These oils are referred to as dry oils and are primarily composed of omega-3 and omega-6. Greasy oils, on the other hand, tend to contain omega-9.