The different types of ceramides.

Alongside cholesterol (25%) and free fatty acids (25%), ceramides are essential lipid components that protect the skin. A healthy epidermis is composed of approximately 50% ceramides, hence their importance. Indeed, ceramides play the role of a "intercellular cement": they are responsible for creating a strong cohesion between the cells of the stratum corneum, thereby ensuring the integrity of the epidermis, slowing down water loss and the penetration of harmful external substances, while providing flexibility.

However, with age or due to external aggressions (UV rays, temperature variations, pollution...), when their content decreases, this leads to a weakening of the skin barrier and a state of skin dryness, thus contributing to dull, rough skin that is more vulnerable to external stress factors and dehydration. This is where ceramide-based treatments come into play to compensate for this deficit and thus rebuild the skin barrier.

Ceramides are polar lipids belonging to the sphingolipid family, structurally heterogeneous and complex, and thus appearing in INCI lists under various names. They result from the combination of a long-chain sphingoid base and a fatty acid via an amide bond.

Whether of synthetic or plant origin, there are different fractions of ceramides depending on the number of carbon atoms in the considered fatty acid (between 16 and 36 carbons), its degree of unsaturation (saturated or mono-unsaturated), and the length of the sphingoid residue chains.

The nomenclature used to identify ceramides is based on a letter code, referring to the chemical modifications of different ceramide species. The first letter informs about the type of fatty acid modification: N represents a non-hydroxylated fatty acid, A an α-hydroxylated fatty acid, O an ω-hydroxylated fatty acid, and EO if the ω-hydroxylated acid is esterified. The second letter defines the type of sphingoid base: S corresponds to sphingosine, P to phytosphingosine, H to 6-hydroxy-sphingosine, dS to dihydroxysphingosine, and T to the dihydroxy-sphinganine.

Note : The initial nomenclature of ceramides was based on a series of numbers from 1 to 8, in accordance with the six ceramide fractions separated by chromatography and identified in human skin. The higher the number, the greater the polarity.

As a result, a total of 18 different species of skin ceramides have been discovered to date: Ceramide AdS (Ceramide 11), Ceramide AH (Ceramide 7), Ceramide AP (Ceramide 6), Ceramide AS (Ceramide 5), Ceramide EAS or 1-O-EAS, Ceramide ENS or 1-O-ENS, Ceramide EOdS, Ceramide EOH (Ceramide 4), Ceramide EOP (Ceramide 9), Ceramide EOS (Ceramide 1), Ceramide OS, Ceramide OH, Ceramide OP, Ceramide NdS or NG (Ceramide 10), Ceramide NH (Ceramide 8), Ceramide NP (Ceramide 3), Ceramide NS (Ceramide 2) and Ceramide NT.

The facts to know about these subclasses of ceramides.

• The ceramides AdS, AH, AP and AS have a structure very similar to the ceramides NdS, NH, NP and NS, but they differ by the hydroxylation of the fatty acid in position α.

• Regarding esterified ceramides, the esterification can occur either on the fatty acid part in the ω position (EO), typically with linoleic acid, or on the primary hydroxyl in position 1 of the sphingoid base (1-O-E), typically with a saturated acyl chain.

• Esterification endows ceramides with enhanced stability against oxidative influences.

• Ceramides, in which the "fatty acid" part is hydroxylated in the ω (O) position, are the least abundant in the stratum corneum of humans.

• The dihydroxysphingosine (dS) type ceramides differ from the sphingosine (S) type by the absence of the trans double bond in the head group, thus making it more permeable to water and various substances.

• The class of ceramides in which the fatty acid part is esterified in the ω position is known as acylceramides.

• Ceramides with a non-hydroxylated fatty acid (N) represent the most abundant group of ceramides in the stratum corneum compared to all ceramide subclasses, particularly the NP and NS ceramides.

  Our lip mask is formulated with NS ceramides that contribute to repairing the skin barrier, in addition to the hyaluronic acid for hydration (INCI name: Sodium Hyaluronate) and the mango butter (INCI name: Mangifera Indica Seed Butter) for nourishment.