Ceramides have become one of the flagship ingredients in the barrier territory of cosmetics. Their scientific legitimacy is solid: as the major constituents of the intercellular lipid matrix of the stratum corneum, they play a decisive structural role in barrier function. But their presence in a formula is not enough to validate a claim. Substantiating a barrier promise built around ceramides requires a structured proof strategy, combining ingredient characterization, in vitro functional evaluation, and in vivo clinical demonstration. This guide details this approach from A to Z.
Ceramides in the stratum corneum: essential scientific foundations
Structure and functional role
Ceramides are sphingolipids composed of a sphingoid base linked to a fatty acid by an amide bond. In the human stratum corneum, they represent approximately 50% of total lipids by mass, alongside free fatty acids (10 to 20%) and cholesterol (25%). This precise composition and the lamellar organization of these lipids into bilayers are directly responsible for the waterproofing function of the stratum corneum.
More than 340 molecular ceramide species are now identified in the human stratum corneum, classified according to the nature of their sphingoid base (sphingosine S, phytosphingosine P, 6-hydroxysphingosine H, dihydrosphingosine dS) and the nature of their fatty acid (non-hydroxylated N, alpha-hydroxylated A, omega-hydroxylated O, ester-linked EO). The major subclasses are designated by their combined nomenclature: CER NS, CER NP, CER EOS, CER EOH, etc.
Ceramide deficits and barrier pathologies
Quantitative and qualitative ceramide deficits in the stratum corneum are documented in several skin conditions:
| Condition | Ceramide alteration |
|---|---|
| Atopic dermatitis | Overall decrease, altered CER NS/NP ratio, shorter acyl chains |
| Psoriasis | Decrease in CER EOS, disruption of lamellar organization |
| Chronic dry skin | Reduction of total ceramides, increase in free fatty acids |
| Ichthyosis | Severe CER EOS deficit, rupture of the bound cornified envelope |
| Skin aging | Progressive decrease in total ceramides and chain shortening |
These data scientifically justify the interest of formulas supplying exogenous ceramides or stimulating their endogenous synthesis to restore barrier function.
Plant-derived, animal-derived, and biotechnological ceramides: what brands need to know
Ceramides used in cosmetics come from three main origins, with different molecular profiles and levels of evidence:
Plant-derived ceramides (phytoceramides): mainly extracted from wheat (Triticum vulgare), rice, or corn. Their structure differs slightly from human ceramides (predominantly phytosphingosine base, shorter acyl chains). Studies show their capacity to improve TEWL and hydration, but direct comparison with human ceramides should be nuanced.
Animal-derived ceramides: mainly from bovine brain (before BSE restrictions) or bone marrow. Rarely used today for regulatory and ethical reasons.
Synthetic and biotechnological ceramides: produced by chemical synthesis or microbial fermentation, they can very precisely mimic the structure of human ceramides (CER NS, CER NP in particular). Some actives such as pseudoceramides or nanoceramides offer improved solubility and better skin bioavailability.
| Origin | Available subclasses | Structural proximity to human ceramides | Available level of evidence |
|---|---|---|---|
| Plant (wheat, rice) | CER NP, CER NS (phyto) | Moderate | High (published clinical studies) |
| Chemical synthesis | CER NS, CER NP, pseudoceramides | High | High |
| Biotechnological | CER NS, NP, EOS | Very high | Growing |
| Animal | CER NS, NP, EOS | Very high | Historical, rarely used |
The substantiation strategy: building a solid file
Step 1: analytical characterization of the ingredient
Before any biological study, the brand must have a precise analytical characterization of its ceramides. Liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS or LC-MS/MS) allows identification and quantification of the ceramide subclasses present in the ingredient and in the finished formula. This step is fundamental: it documents what the formula actually delivers, and establishes the link with clinical data.
Step 2: in vitro evaluation of the mechanism of action
In vitro studies on cell models or reconstructed epidermis allow demonstration of the mechanism of action before launching a costly clinical study. The most relevant approaches for ceramide formulas are:
On 3D reconstructed epidermis (EPI-200, SkinEthic RHE):
- Measurement of transepithelial electrical resistance (TEER) before and after treatment: direct indicator of barrier integrity
- Permeability evaluation by diffusion of labeled molecules (Franz cell)
- Quantification of ceramides integrated into the lipid matrix by LC-MS/MS after extraction
- Gene and protein expression of epidermal differentiation (filaggrin, loricrin, transglutaminases)
On keratinocytes in culture:
- Expression of serine palmitoyl transferase (SPT), the key enzyme of ceramide biosynthesis
- Quantification of endogenous ceramide synthesis after treatment
- Expression of caspase-14 (involved in filaggrin degradation and NMF production)
Step 3: in vivo clinical demonstration
In vivo demonstration is at the heart of the substantiation file. It must answer two questions: does the formula improve the functional parameters of the barrier? And does it do so via the ceramides?
Biometrological parameters:
| Parameter | Equipment | What it demonstrates |
|---|---|---|
| TEWL | Tewameter, Aquaflux | Improvement of barrier permeability |
| SC hydration | Corneometer® | Improvement of corneal hydration |
| SC lipid profile | Tape stripping + LC-MS/MS | In situ restoration of ceramide subclasses |
| Lipid organization | Raman, FTIR-ATR on strips | Reorganization of the intercellular matrix |
| Epidermal differentiation | Tape stripping + ELISA/Western blot | Filaggrin, loricrin, caspase-14 expression |
Recommended target populations:
- Dry to very dry skin: measurable hydrating and repairing effect
- Mild to moderate atopic skin (outside flares): documented ceramide deficit, relevant population for barrier restoration claims
- Mature skin (50 years and over): physiological ceramide decline, suitable population for anti-aging barrier claims
Possible claims and required level of evidence
Ceramide claims fall into several levels, each calling for a specific level of evidence:
Functional claims (standard level of evidence):
- “Strengthens the skin barrier” → TEWL + Corneometer before/after, healthy or dry skin, D0/D28
- “Improves hydration” → Corneometer, classic design
- “Suitable for sensitive skin” → TEWL + irritation scores + neurosensory evaluation
Mechanistic claims (high level of evidence):
- “Restores ceramides in the stratum corneum” → tape stripping + LC-MS/MS in vivo, comparison of subclasses before/after treatment
- “Stimulates natural ceramide synthesis” → in vitro study on keratinocytes or reconstructed epidermis, quantification of endogenous biosynthesis
- “Reconstitutes the intercellular lipid matrix” → FTIR-ATR or Raman on tape stripping strips, visualization of lamellar organization
Comparative or superlative claims: require a study versus an active comparator or versus placebo with randomization, and a statistically pre-calculated sample size.
Regulatory considerations
In Europe, cosmetic claims are governed by Regulation (EC) No. 655/2013 and the European Commission guidelines. Ceramide claims must comply with the six common criteria: legal compliance, truthfulness, evidential support, honesty, fairness, and informed decision-making.
Claims involving action on skin pathologies (atopic dermatitis, psoriasis) cross into the territory of medicines or medical devices depending on the level of promise — a line not to be crossed in a cosmetic file. Claims on “atopic skin” are acceptable if they remain on the grounds of comfort and tolerance, not treatment.
Selecting the right laboratory for a ceramide study
A CRO capable of substantiating ceramide claims must bring together several competencies rarely available in a single establishment:
- Skin biometrology (TEWL, Corneometer) with a controlled room
- Tape stripping with a standardized protocol
- Lipidomics (LC-MS/MS) for ceramide subclass analysis
- Spectroscopy (Raman or FTIR-ATR) for lipid organization
- In vitro models (reconstructed epidermis, keratinocytes) for mechanism of action
Few CROs offer all of these capabilities in-house. Selection may therefore involve a primary CRO for in vivo studies and a specialized analytical laboratory for lipidomics.
On the Skinobs platform, brands can filter laboratories by method and identify experts in stratum corneum lipidomics, analytical tape stripping, and studies on atopic or dry skin, among the 138 referenced laboratories in 38 countries.
Conclusion
Substantiating a ceramide claim does not come down to proving that the formula hydrates. It means demonstrating that the ceramides delivered by the formula integrate into the lipid matrix of the stratum corneum, restore its organization, and measurably improve barrier function. This chain of evidence — from analytical characterization of the ingredient to in vivo clinical demonstration — is today the expected standard for the most solid and defensible barrier claims.
Looking for laboratories adapted to substantiate your ceramide claims? Skinobs allows you to identify CROs expert in stratum corneum lipidomics and barrier studies. [Access the platform]
