This is a comprehensive guide to understand what is the exact difference between a penetrating and a coating oil and which oils to use depending on your afro hair type.
Composition of vegetable oils
Vegetable oils are made by pressing or extraction from fatty fruits (olive, avocado…), beans (cocoa) or seeds (peanuts, corn, sesame …).
Oils have softening properties and, depending on their composition, will generate a more or less occlusive fat film.
Vegetable oils consist primarily of triglycerides of fatty acids.
These triglycerides are responsible for the softening qualities of vegetable oils.
Triglycerides and fatty acids
Triglycerides consist of 3 fatty acids attached to a glycerol molecule.
These 3 fatty acids of a triglyceride molecule may be identical, nonetheless, they are most often different.
There are two kinds of fatty acids: saturated fatty acids and unsaturated fatty acids.
Saturated fatty acids do not contain double bonds. Lauric acid is a saturated fatty acid present in large quantities in coconut oil.
Oils possessing a high amount of saturated fatty acids are generally very stable and do not oxidize easily.
Besides, as the structure of saturated fatty acids is relatively simple, they are more readily compacted together.
Consequently, oils containing high concentrations of saturated fatty acids are solid at room temperature (like coconut oil).
Unsaturated fatty acids include one or more double bonds (equally known as unsaturations). Oleic acid found in olive oil has 1 double bond.
The double bond of an unsaturated fatty acid creates a “bend” in the molecule.
Hence, the more double bonds the fatty acid contains, the more complex its structure will be.
Because of their cumbersome structure, the fatty acids present in the oil compact together with difficulty.
And, as a result, oils containing large amounts of unsaturated fatty acids are liquid at ambient temperature.
Furthermore, the more double bonds the fatty acid incorporates, the higher the rate of oxidation, and the faster the oil turns rancid.
Depending on their fatty acid composition, oils will be able to progressively penetrate the hair fibre or else to remain on the surface of the cuticle.
Penetrating oils and natural afro hair
Properties of penetrating oils
The ability of an oil to penetrate the hair depends on its fatty acid composition. As a matter of fact, the shorter fatty acids are included in the oil, the more the oil is able to infiltrate the hair fiber.
Additionally, certain fatty acids display a slight positive charge and will be attracted by the negative charges of the hair proteins.
These so-called “polar” fatty acids present a high affinity for hair proteins .
Which are the penetrating oils?
Coconut oil [INCI: Cocos Nucifera (Coconut) Oil] contains lauric acid.
This small fatty acid has a strong affinity for hair proteins.
When applied to the hair, this oil is able to penetrate deeply into the cortex and to diminish protein loss .
Murumuru Butter [INCI: Astrocaryum Murumuru Seed Butter] and Babassu Oil [INCI: Orbignya Oleifera (Babassu) Seed Oil)] also include a high amount of lauric acid and would as well be able to penetrate the hair.
Sunflower oil [INCI: Helianthus Annuus (Sunflower) Seed Oil)], avocado [INCI: Persea Gratissima (Avocado) Oil)] and olive oil [INCI: Olea Europaea (Olive) Oil] equally have the ability to infiltrate the hair, however just in a superficial way , .
The oils listed above are the only oils studied by the scientific community for their penetration property.
This does not mean that other oils are not able to penetrate the hair. They have not been the subject of studies yet.
What types of hair will benefit from the advantages of penetrating oils?
Penetrating oils are especially effective on hair damaged by excessive heat, handling or colouring. In fact, damaged hair has a porous cuticle.
When immersed in water, it will absorb a large amount of water and will excessively swell. Their cuticle will rise and can break more readily, which will make the hair even more porous.
Furthermore, too much water in the hair will undermine the proteins of the cortex and will make the hair extremely elastic.
The disproportionate absorption of water, followed by a repeated shrinking of the hair fibre (hygral fatigue) will also weaken the hair.
The use of a penetrating oil will regulate the entry of water into the hair fibre. The oil will seize the free space in the hair and, as a result, will slow down the water influx.
Besides, it will make the hair more likely to repel water and a healthy hair is a hydrophobic hair (which does not like water).
How to use penetrating oils?
Penetrating oils are particularly effective on damaged and porous hair as a pre-shampoo oil treatment. Allow working all night for maximum absorption.
The heat also facilitates the penetration of oils into the hair.
Do you need to apply your pre shampoo oil treatment on dry or damp hair? Click for more information.
Taking into account that these oils will penetrate the hair fibre, their presence on the surface of the hair will slowly diminish in favour of the cortex.
Penetrating oils are therefore less effective in retaining moisture in the hair and reducing frizz (as in the LOC method, for example).
Coating oils and afro textured hair
Properties of coating oils
Due to their composition rich in long and unsaturated fatty acids, these oils cannot infiltrate the hair fibre.
Non-penetrating oils have the ability to create a film around the hair, which will:
- limit the evaporation of water and thus keep the hair hydrated longer,
- diminish water absorption, reduce frizz and preserve the styling for a longer time.
Which are coating oils?
These are all other oils other than coconut, babassu, sunflower, olive and avocado oil.
Contrarily to its name, Jojoba Oil [INCI: Simmondsia Chinensis (Jojoba) Seed Oil] is not an oil but a liquid wax.
While vegetable oils are predominantly made up of triglycerides, jojoba oil is rich in waxy esters.
Its composition is close to that of the human sebum .
Use of non-penetrating oils
Coating oils are suitable for all types of hair. They are extremely efficient for damaged hair as a sealing oil after application of leave-in.
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- Robbins CR. Chemical and Physical Behavior of Human Hair. 4th ed. New York: Springer; 2013
- Rele, Aarti S., and R. B. Mohile. “Effect of mineral oil, sunflower oil, and coconut oil on prevention of hair damage.” Journal of cosmetic science 54.2 (2002): 175-192.
- International Journal of Cosmetic Science, Pages 78 – 78, 2006
- Keis K, Persaud D, Kamath YK, Rele AS. Investigation of penetration abilities of various oils into human hair fibers. J Cosmet Sci. 2005;56:283–95.
- Jojoba Oil Wax Esters and Derived Fatty Acids and Alcohols: Gas Chromatographic Analyses. THOMAS K. MIWA, Northern Regional Research Laboratory Peoria, Illinois 61604.