Are vegetable oils comedogenic?

A comedogenic vegetable oil is prone to causing comedones.

This is an important factor to check before using a vegetable oil, especially on combination or oily skin. These so-called comedogenic oils have an oily texture and can form a semi-occlusive film on the skin’s surface. While this film helps prevent transepidermal water loss, it can impede normal sebum release by blocking the skin’s pores, which leads to the appearance of blackheads or whiteheads. Not all vegetable oils are equal in terms of comedogenicity. Several factors influence their pore-blocking potential, including:

• Sensitivity to oxidation and freshness of vegetable oil.

  Some vegetable oils are more prone to oxidation than others. Oils rich in antioxidants and containing a majority of saturated fatty acids—meaning they have no double bonds liable to react with an oxidant—are more stable than oils low in antioxidants with a high proportion of unsaturated fatty acids. However, when a vegetable oil oxidises, its organoleptic properties change : it becomes thicker and more comedogenic. Several factors can cause this oxidation, such as exposure to oxygen in air, light, heat, or interactions with the container.

• The quality of plant oil.

  A vegetable oil obtained by cold-press extraction is often less comedogenic. This process requires no chemical treatment or exposure to high temperatures, which can degrade certain fatty acids and generate new compounds not necessarily beneficial for the skin.

• Rate of plant oil penetration into the epidermis.

  A thick, fatty vegetable oil is poorly absorbed by skin, which may increase its occlusive nature. Conversely, the greater an oil’s affinity with skin, the higher its penetration. These oils are classed as dry and are mainly composed of omega-3s, such as alpha-linolenic acid, and omega-6s, such as linoleic acid. Fatty oils, by contrast, contain mainly omega-9s, such as oleic acid.

Every plant oil has a comedogenic index, determined by analysis of freshness, oxidation level and rate of skin penetration.

Comedogenicity of vegetable oils is traditionally measured on a scale of zero to five.

• Rating 0: It indicates the vegetable oil is non-comedogenic and suits combination to oily and/or blemish-prone skin. These oils include argan oil, hemp oil, prickly pear oil, jojoba oil and hazelnut oil.

• Index 1 to 2: This category includes oils with low comedogenicity, such assweet almond oil, apricot oil, castor oil or nigella oil.

• Comedogenicity ratings 3 and 4: Oils with a comedogenicity rating of 3 or 4 have moderate comedogenic potential. These include coconut oil, flaxseed oil, rosehip oil and soybean oil.

• Index 5: A vegetable oil with an index of 5 has strong comedogenic potential, such as wheat germ oil.

Combination and oily skin types should select vegetable oils with a low comedogenicity rating (0 to 2). Normal to dry skin types may use oils rated between 0 and 5. Contrary to common belief, skin prone to blemishes does not need to avoid vegetable oils: it simply needs to choose the most suitable ones. A comedogenic vegetable oil in a product does not necessarily cause blemishes. Its concentration, the formula’s delivery system, synergy with other ingredients, and the user’s skin type are key factors.

Determining whether a vegetable oil is comedogenic based on texture can be difficult. If you are uncertain, we suggest referring to the table below, which lists the main vegetable oils used in skincare and their comedogenicity.

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

• DINARDO J. C. & al. A re-evaluation of the comedogenicity concept. Journal of the American Academy of Dermatology (2006).

• SHOJAN A. & al. Comedogenicity of oils. International Journal of Contemporary Medical Research (2019).