When used in their pure form, comedogenic oils can cause or exacerbate skin problems such as acne. Therefore, it is beneficial for individuals prone to such issues to research the comedogenicity of vegetable oils. What about castor oil? Let's explore its comedogenic potential together.
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Is castor oil among the so-called comedogenic oils?
Summary
Published August 26, 2024,
updated on October 4, 2024,
by
Pauline, Chemical Engineer
—
5 min read
Is castor oil comedogenic?
Typically obtained through cold pressing of the seeds of the common castor oil plant, the castor oil is commonly used in cosmetic formulation. This vegetable oil, rich in fatty acids and vitamins, can also be used pure directly on the skin or hair, exerting its various properties (moisturising, nourishing, soothing, healing...). However, for those with oily or acne-prone skin, applying a vegetable oil purely to the face is not a trivial matter, due to their fear of new imperfections appearing. To prevent this inconvenience, it is good to question the comedogenicity of vegetable oils.
As a reminder, an oil is said to be comedogenic when it has the potential to clog the pores of the skin and promote the appearance of comedones. Vegetable oils are classified on a scale ranging from 0 to 5, defining a comedogenicity index. An ingredient with an index of 0 is non-comedogenic. From 1 to 2, it is considered slightly comedogenic. An index above 3 indicates that the vegetable oil is comedogenic. Several criteria, presented in the table below, are taken into account to assess the comedogenicity of an ingredient.
| Texture | Oxidation Sensitivity | Extraction Process | Freshness |
|---|---|---|---|
| Oils with a viscous texture are more likely to clog the pores of the skin. | Oils that are sensitive to oxidation are generally more comedogenic. | Cold-press extraction allows the constituents of oils not to be exposed to high temperatures, which could potentially degrade them and lead to the formation of comedogenic compounds. | If stored for too long or exposed to light or heat, vegetable oils can oxidise and become comedogenic. |
Récapitulatif des critères évaluant la comédogénicité d'une huile végétale.
With that being said, let's turn our attention to the organoleptic characteristics of castor oil. This transparent to golden liquid with a rather strong smell has a relatively greasy texture, which is derived from its biochemical composition. Indeed, castor oil is predominantly composed of ricinoleic acid (80 - 90%), a monounsaturated fatty acid. However, the single double bond in its chemical structure does not provide it with much flexibility, unlike polyunsaturated fatty acids, which have several double bonds. This lack of flexibility in the main compound of castor oil translates at the macroscopic level into a certain viscosity, suggesting that castor oil is a comedogenic oil.
However, the relatively greasy texture of castor oil is offset by its excellent stability to oxidation, which can be explained in two ways. Firstly, it's important to remember that the main oxidation reactions affecting vegetable oils occur between an oxidant, such as atmospheric oxygen, and a double bond carried by an unsaturated fatty acid. Given that castor oil primarily contains monounsaturated fatty acids, the likelihood of it oxidising is quite reduced. Furthermore, the fatty acids in castor oil are protected by its richness in vitamin E, a powerful antioxidant sometimes used as a preservative in oily formulations.
Castor oil is considered a low comedogenic oil. Its comedogenicity index is 1.
Note : Even though castor oil naturally tends to be non-comedogenic, its occlusive nature can be increased by poor storage. Once opened, castor oil should be kept for a maximum of six months, in a tightly sealed bottle and protected from sunlight and heat. Furthermore, as specified in the table above, it is generally recommended to opt for a vegetable oil obtained by cold pressing.
Sources
STAVRIANEAS N. G. & et al. Comedogenicity of Cosmetics: A Review. Journal of the European Academy of Dermatology and Venereology (1996).
DINARDO J. & al. A Reassessment of the Comedogenicity Concept. Journal of the American Academy of Dermatology (2006).
TESSEMA S. & al. Physicochemical Characterisation and Evaluation of Castor Oil (R. communis) for Hair Biocosmetics. American Journal of Applied Chemistry (2019).
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