Understanding Ceramides from the Perspective of the Stratum Corneum Lipid Barrier: Moisturizing and Barrier-Repair Mechanisms, Ingredient Selection, and Formulation Research Considerations

Introduction

When the skin feels dry, tight, stinging, or red, many people immediately attribute it to “dehydration.” However, in skincare evaluation, the more important question is often not whether water has been temporarily replenished, but whether the stratum corneum can effectively reduce water loss and limit the entry of external irritants.

This is where the value of ceramides lies. Ceramides are not ordinary hydrating ingredients; they are important components of the stratum corneum lipid barrier. The stratum corneum is not simply a layer of cells covering the skin surface. Rather, it is a protective structure composed of corneocytes and intercellular lipids. Among these, ceramides, cholesterol, and free fatty acids together form the intercellular lipid layer, directly influencing the skin’s water-retention capacity and barrier stability.

1 The Core of the Skin Barrier: The Lipid Structure of the Stratum Corneum

1.1 The stratum corneum is a protective structure composed of both cells and lipids

The outermost layer of the skin is the stratum corneum (SC). The stratum corneum is the key site responsible for skin barrier function and mainly performs two tasks: reducing the outward loss of water from the body and lowering the chance that external irritants, allergens, and microbe-associated components enter the skin.

The stratum corneum is composed of two core structural components:

Component	Main Role
Corneocytes	Provide mechanical support and form the basic framework of the stratum corneum
Intercellular lipids	Fill the spaces between corneocytes and form a continuous lipid barrier

1.2 The position of ceramides in the skin barrier

Skin barrier structure and the site of ceramide action

External environment

Irritants / allergens / pollutants / microbe-associated components

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Stratum corneum, SC

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Role of corneocytes: form the basic framework of the stratum corneum

Role of the intercellular lipid layer: fill the spaces between corneocytes and form a continuous barrier

Main lipid composition: ceramides + cholesterol + free fatty acids

Barrier outcome: reduced outward water loss; reduced entry of irritants; maintenance of skin hydration and tolerance

1.3 Why impaired barrier function can lead to dryness and sensitive-skin symptoms

When the intercellular lipid structure of the stratum corneum is intact, skin water is less likely to be lost in large amounts, and external irritants are less likely to penetrate the stratum corneum. Conversely, when the lipid structure is disrupted, or when ceramide content and the proportions of different ceramide types become abnormal, barrier function declines.

Transepidermal water loss (TEWL) is an important indicator used to evaluate skin barrier function. An increase in TEWL indicates that water is more likely to diffuse outward from within the skin. Common manifestations include dryness, tightness, roughness, and flaking. At the same time, external irritants can enter the skin more easily, and the skin may show stinging, redness, a burning sensation, and reduced tolerance to skincare products.

2 What Are Ceramides?

2.1 Ceramides are a class of sphingolipids

Ceramides are a class of sphingolipid molecules. A typical ceramide is composed of a sphingoid long-chain base and a fatty acid, connected by an amide bond. The long-chain base may include structures such as sphingosine, dihydrosphingosine, and phytosphingosine.

Structural Part	Functional Significance
Long-chain sphingoid backbone	Forms the basic backbone of the ceramide molecule
Fatty acid chain	Enhances the hydrophobicity and ordering ability of the lipid molecule
Amide bond	Connects the sphingoid backbone and fatty acid chain to form the ceramide structure

2.2 The properties of ceramides make them suitable for barrier construction

Ceramides have long-chain lipid structures and strong hydrophobicity. They can form an orderly arranged lipid layer together with cholesterol and free fatty acids. This lipid layer has relatively low fluidity and strong blocking capacity, helping the stratum corneum regulate water and external substances.

The role of ceramides can be summarized as follows:

Long-chain lipid structure

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Co-arrangement with cholesterol and free fatty acids

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Formation of the intercellular lipid barrier in the stratum corneum

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Reduction of outward water loss

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Improvement of skin barrier stability

2.3 Ceramides exist in multiple types, and different structures perform different roles

Ceramides in human skin are not a single substance, but consist of multiple subclasses. Common examples include Ceramide NP, Ceramide AP, Ceramide EOP, and Ceramide NS. These names usually represent different structural categories or INCI naming categories and do not necessarily correspond to a single fixed molecule. Within the same category, multiple molecular species may still exist due to differences in fatty acid chain length, degree of unsaturation, and hydroxyl structure.

Among them, ω-O-acylceramides are a class of ceramides with ultra-long N-acyl chains and a linoleic acid esterified structure attached at the ω position. Studies suggest that this class of ceramides is closely related to the long-period lamellar lipid structure of the stratum corneum, the corneocyte lipid envelope, and the integrity of the skin barrier.

3 The Relationship Between Ceramides and Skin Condition

3.1 Ceramide deficiency can affect lipid organization in the stratum corneum

Ceramides are important components of the intercellular lipids in the stratum corneum. When ceramide content decreases, fatty acid chain length changes, or the proportions of different ceramide subclasses become imbalanced, the lipid organization in the stratum corneum may become incomplete, and the continuity of the barrier structure may decline. This change can affect two skin functions:

Affected Function	Possible Manifestations
Reduced water-retention capacity	Dryness, tightness, roughness, flaking
Reduced ability to block external irritants	Stinging, redness, burning sensation, intolerance to skincare products

These symptoms are not necessarily caused only by reduced ceramide levels. They may also be related to over-cleansing, low environmental humidity, ultraviolet exposure, inflammatory responses, skin disease conditions, or highly irritating skincare practices. However, from the perspective of barrier structure, ceramide abnormalities are an important factor worth focusing on.

3.2 Dryness does not always require ceramides, but ceramides deserve more attention when barrier function is impaired

Skin dryness can have different causes. Some dryness is mainly related to low environmental humidity or transient water reduction after cleansing. Other types of dryness are accompanied by tightness, flaking, stinging, redness, and reduced tolerance, suggesting that barrier function may be affected. The following signs can be used for assessment:

Skin Manifestation	Possible Indication
Tightness persists for a long time after cleansing	Loss of stratum corneum lipids or reduced barrier stability
Recurrent dryness and redness during seasonal changes	Reduced ability of the barrier to adapt to temperature and humidity changes
Stinging after using acid-based or vitamin A products	Combined burden of active-ingredient irritation and barrier stress
Roughness, flaking, and repeated instability	Possible abnormalities in stratum corneum hydration and lipid organization
Reduced tolerance to skincare products	External ingredients are more likely to irritate the skin

Vitamin A products refer to skincare or pharmaceutical ingredients that affect keratinization and renewal, such as retinol, retinal, and retinoic acid derivatives.

4 The Role of Ceramides in Skin Care

4.1 The core role of ceramides is to support the barrier lipid structure

In skincare, the main significance of ceramides is to supplement lipids related to the stratum corneum barrier and support the integrity of the intercellular lipid layer, thereby helping reduce outward water loss and improve discomfort associated with dryness, tightness, and impaired barrier function. Their role differs from that of humectants:

Ingredient Type	Representative Ingredients	Main Role
Humectants	Glycerin, hyaluronic acid, betaine	Increase the water content of the stratum corneum
Barrier lipid ingredients	Ceramides, cholesterol, free fatty acids	Support the intercellular lipid structure
Emollient and occlusive ingredients	Squalane, plant oils, silicones	Reduce further water loss and improve skin softness and smoothness

4.2 Ceramides alone cannot complete all barrier repair

Ceramides are important, but barrier recovery is not a process that can be completed independently by a single ingredient. If frequent exfoliation, harsh cleansing, high-frequency use of acid-based products, or layering of high-concentration active ingredients continues at the same time, the barrier may remain under stress. Reasonable skincare approaches include:

Care Objective	Corresponding Approach
Reduce lipid loss	Use mild cleansing products and avoid over-cleansing
Support the lipid barrier	Choose leave-on products containing ceramides, cholesterol, and free fatty acids
Reduce accumulated irritation	When the barrier is unstable, reduce the frequency of acid-based and vitamin A products
Maintain hydration	Pair with moisturizing ingredients such as glycerin, hyaluronic acid, and panthenol
Reduce external damage	Use sun protection during the day to reduce the impact of ultraviolet radiation on the skin

5 The Relationship Between Ceramides and Niacinamide

5.1 They belong to different types of skincare ingredients

Niacinamide, also known as nicotinamide, is a form of vitamin B3 and is a water-soluble small-molecule active ingredient. Ceramides, by contrast, are lipid-based barrier ingredients. They are not the same type of ingredient and differ in their sites and modes of action:

Comparison Dimension	Ceramides	Niacinamide
Ingredient category	Sphingolipid barrier lipids	Vitamin B3 derivative
Main direction of action	Participate in the lipid structure of the stratum corneum	Participate in epidermal cell metabolism and barrier-related processes
Relationship with the barrier	Serve as important components of intercellular lipids	May promote the synthesis of ceramides and other stratum corneum lipids
Skincare focus	Dryness, tightness, impaired barrier function	Barrier support, while also addressing skin tone, sebum, and inflammation-related concerns
Usage considerations	Focus on the overall combination system and product mildness	Excessively high concentrations or unstable barrier conditions may cause irritation

5.2 Ceramides mainly supplement barrier lipids, while niacinamide mainly supports lipid synthesis

Research shows that, under appropriate concentrations and formulation conditions, niacinamide can promote keratinocytes to synthesize ceramides and other stratum corneum lipids. Topical niacinamide has also been observed to increase levels of ceramides and free fatty acids in the stratum corneum and reduce transepidermal water loss, or TEWL, in dry skin.

Ceramides and niacinamide are complementary:

Key role of ceramides: supplement barrier-related lipid components

Key role of niacinamide: promote the skin’s own synthesis of ceramides and other lipids

Logic of combined use: exogenous lipid supplementation + support for endogenous lipid synthesis

This is also why some barrier-care products contain both ceramides and niacinamide. Ceramides are more focused on structural supplementation, while niacinamide is more focused on physiological regulation. When used together, they can support stratum corneum barrier function through different pathways.

5.3 How to choose based on skin condition

Skin Condition	Suitable Choice
Dryness, tightness, flaking, accompanied by stinging or redness	Prioritize ceramide-based barrier-care products
Dull skin tone, higher sebum production, and generally good barrier tolerance	Consider niacinamide-based products
Reduced tolerance after using acid-based or vitamin A products	Prioritize ceramide-related barrier care and reduce the frequency of irritating active ingredients
Desire to maintain long-term skin stability	Choose products combining ceramides and niacinamide
Noticeable stinging after using niacinamide	Reduce the concentration or frequency of use and first improve the barrier condition

6 How to Evaluate Whether a Ceramide Product Is Worth Choosing

6.1 Do not only check whether ceramides are added; assess whether the overall formulation is designed around barrier care

The presence of “Ceramide” in an ingredient list does not necessarily mean the product is suitable for a compromised barrier. Ceramides are relatively lipophilic, and their stability, dispersion, skin feel, and performance are influenced by the formulation system. It is recommended to consider whether the product addresses the following aspects:

Evaluation Dimension	Key Points to Consider
Barrier lipid supplementation	Whether it contains lipid ingredients such as ceramides, cholesterol, and free fatty acids
Moisturizing support	Whether it contains humectants such as glycerin, hyaluronic acid, and betaine
Soothing support	Whether it contains ingredients such as panthenol, allantoin, and madecassoside to reduce discomfort associated with dryness
Formulation mildness	Whether it reduces highly irritating fragrances, highly volatile alcohols, and high-concentration irritating active ingredients
Product type	Whether it is a leave-on product such as a lotion, cream, or repair serum

In addition, the dissolution, dispersion, carrier system, and ratio of ceramides to cholesterol and fatty acids in the final formulation can all affect their actual performance in barrier care.

6.2 When the barrier is unstable, reduce irritation first before pursuing repair efficiency

If the skin already shows signs of impaired barrier function, such as tightness, stinging, redness, and flaking, the skincare sequence should begin with subtraction before addition.

Skincare sequence for an unstable barrier:

① Reduce sources of irritation: reduce harsh cleansing, frequent exfoliation, high-frequency use of acid-based products, and vitamin A products

② Maintain basic moisturization: use mild moisturizing ingredients such as glycerin, hyaluronic acid, and panthenol

③ Supplement barrier lipids: choose leave-on products containing ceramides, cholesterol, and free fatty acids

④ After the skin stabilizes, gradually resume function-oriented skincare: such as brightening, anti-aging, and oil-control active ingredients

7 Representative Chemical Product Classification Tables Related to Ceramides and the Stratum Corneum Lipid Barrier

Table 1 Ceramide Compounds, Model Compounds, and Sphingolipid Metabolism-Related Products

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Ceramide compound	178436-06-1	C995092	Ceramide NP	≥95%	A stratum corneum intercellular lipid-related component, used for ceramide structure research, barrier lipid model construction, and skin lipidomics analysis
Ceramide compound	100403-19-8	C647629	Ceramide mixture	≥95%	A multi-component ceramide material, used for simulating the ceramide composition of the stratum corneum, studying barrier lipid combinations, and developing repair-oriented formulations
Ceramide compound	34354-88-6	N339996	N-Stearoyl phytosphingosine	≥98%	A phytosphingosine-type ceramide, used for studying stratum corneum lipid organization, analyzing the effect of ceramide chain length, and conducting barrier lipid model experiments
Short-chain ceramide model compound	3102-57-6	C769948	N-Acetyl-D-sphingosine	Moligand™, ≥98%	A short-chain ceramide model compound, used for sphingolipid signaling research, evaluation of ceramide bioactivity, and cell-level mechanistic studies
Short-chain ceramide model compound	124753-97-5	N130615	N-Hexanoyl-D-erythro-sphingosine	≥99%	A short-chain ceramide research reagent, used for studying ceramide signaling pathways, cell apoptosis and differentiation experiments, and lipid metabolism regulation research
Dihydroceramide	2304-80-5	N130689	C18 Dihydroceramide (d18:0/18:0)	≥99%	A dihydroceramide reference compound, used for sphingolipid metabolic pathway research, analysis of the conversion between dihydroceramides and ceramides, and lipidomics detection
Sphingosine base	123-78-4	D130604	D-erythro-Sphingosine	Moligand™, ≥99%	A ceramide structural-unit-related reagent, used for sphingolipid metabolism research, analysis of ceramide biosynthetic pathways, and cell signaling experiments
Dihydrosphingosine base	764-22-7	D130610	D-erythro-Dihydrosphingosine	Moligand™, ≥95%	A dihydrosphingosine-related reagent, used for research on dihydroceramide precursors, sphingolipid biosynthesis analysis, and lipid metabolism experiments
Phytosphingosine base	554-62-1	D136389	Phytosphingosine (glycolipid)	≥98%	A phytosphingosine-type sphingoid base-related product, used for ceramide structural-unit research, sphingolipid metabolism experiments, and studies related to stratum corneum lipids
Sphingomyelin	85187-10-6	S414640	Sphingomyelins（SM） (from bovine spinal cord)	≥95% natural bovine mixture	Naturally derived sphingomyelin, used for ceramide metabolic pathway research, membrane lipid model construction, and studies of sphingolipid hydrolysis and lipid signaling

Table 2 Barrier Sterol and Free Fatty Acid-Related Products

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Barrier sterol	57-88-5	C432977	Cholesterol, plant-derived	≥98%	A key sterol component of stratum corneum intercellular lipids, used for constructing ternary lipid models composed of ceramides, cholesterol, and free fatty acids
Essential fatty acid	60-33-3	L100441	Linoleic acid	Moligand™, ≥99% (GC)	An unsaturated fatty acid component, used for research on linoleic-acid-related ceramide structures, analysis of stratum corneum lipid composition, and barrier lipid model experiments
Saturated fatty acid	57-10-3	P753896	Palmitic acid	Stearic acid ≤0.5%	A saturated fatty acid component, used for studying skin free fatty acid systems, barrier lipid combinations, and structural regulation of emulsification systems
Saturated fatty acid	57-11-4	S736443	Stearic acid	Moligand™, ≥95%, acid value 194–199 mg KOH/g	A long-chain saturated fatty acid, used for stratum corneum lipid models, structural regulation of cream systems, and barrier-care formulation research
Unsaturated fatty acid	112-80-1	O1456059	Oleic acid	USP, ≥98%	A monounsaturated fatty acid component, used for skin lipid fluidity research, transdermal penetration studies, and lipid system construction; in barrier-care applications, it is suitable as a research model for lipid fluidity or penetration enhancement
Long-chain/very-long-chain saturated fatty acid model	112-85-6	B754990	Behenic acid, also known as moringa seed oil acid	≥99%	A C22:0 saturated fatty acid-related product, used for studying fatty acid chain-length effects, analyzing ordered arrangement of lipid layers, and constructing barrier lipid models
Long-chain/very-long-chain saturated fatty acid model	557-59-5	L131579	Lignoceric acid	≥99% (GC)	A C24:0 saturated fatty acid, used for studying fatty acid chain-length effects, analyzing ceramide chain-length-related properties, and conducting barrier model experiments

Table 3 Niacinamide, Moisturizing, and Soothing Auxiliary Products

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Vitamin B3 barrier-regulating ingredient	98-92-0	N108086	Niacinamide	≥99.5% (HPLC)	A vitamin B3 active ingredient, used for research on promoting ceramide synthesis, transepidermal water loss evaluation, and development of barrier-function-regulating formulations
Vitamin B3 control ingredient	59-67-6	N103652	Niacin	Moligand™, ≥99%	A vitamin B3-related ingredient, used for niacinamide metabolism-related research, control experiments for skin active ingredients, and analysis of barrier-regulating mechanisms
Macromolecular aqueous-phase moisturizing ingredient	9067-32-7	S1519982	Sodium hyaluronate	Injection grade, ≥99.8%, molecular weight: 1.70–2.60 million	A high-molecular-weight moisturizing ingredient, used for evaluating stratum corneum hydration, constructing the aqueous phase of moisturizing systems, and developing barrier-care formulations
Polyol moisturizing ingredient	56-81-5	G755728	Glycerol	Anhydrous grade, UltraBio™, molecular biology grade, ≥99.5% (GC)	A humectant, used for stratum corneum hydration research, construction of basic moisturizing systems, and development of ceramide combination formulations
Natural moisturizing factor-related ingredient	28874-51-3	L303332	Sodium L-pyrrolidone-5-carboxylate	Oily, 50%	A natural moisturizing factor-related ingredient, used for studying water retention in the stratum corneum, moisturizing system design, and barrier-care formulation development
Natural moisturizing factor-related ingredient	57-13-6	U111897	Urea	AR, ≥99%	A natural moisturizing factor-related ingredient, used for stratum corneum hydration research, dry-skin model experiments, and moisturizing repair formulation development; at low concentrations it mainly supports moisturization, while at higher concentrations it may have keratin-softening or keratin-conditioning effects, so irritation should be considered when the barrier is unstable
Osmoregulating moisturizing ingredient	107-43-7	B105556	Betaine, anhydrous	Moligand™, ultrapure grade, ≥99%	An ingredient with both moisturizing and osmoregulatory properties, used for hydration-balance research, mild moisturizing systems, and barrier-care formulation development
Panthenol care auxiliary ingredient	81-13-0	P107368	D-Panthenol	≥98%	A panthenol-type care auxiliary ingredient, used for research on improving dryness-related discomfort, barrier-care formulations, and moisturizing-soothing systems
Panthenol care auxiliary ingredient	16485-10-2	P117668	DL-Panthenol	≥99%	A panthenol-type moisturizing and soothing ingredient, used for basic moisturizing formulations, barrier-care systems, and experiments on improving dry skin conditions
Soothing care auxiliary ingredient	97-59-6	A101660	Allantoin	≥98%	A commonly used soothing care ingredient, used for dry and rough skin care research, barrier-care formulations, and mild repair systems

Table 4 Sebum-Related Emollient Lipid Products

Category	CAS No.	Aladdin Catalog No.	Name	Specification or Purity	Product Features and Applications
Sebum-related unsaturated lipid	111-02-4	S109119	Squalene	Moligand™, ≥98%	A sebum-related unsaturated lipid, used for skin lipid composition research, lipid oxidation experiments, and prototype research on emollient systems; as an unsaturated lipid, its oxidative stability should be considered
Sebum-related emollient lipid	111-01-3	S141335	Squalane	≥98%	A stable emollient lipid ingredient, used for barrier-care formulations, skin-feel adjustment in cream systems, and research related to reducing outward water loss

Note: The above products are mainly intended for scientific research, analytical testing, lipid model construction, and formulation prototype studies. Whether they can be used in cosmetics, human-use products, or large-scale formulations should be determined based on product grade, regulatory requirements, COA/SDS, supply status, and compliance evaluation. For more product specifications, grades, and COA information, please search by “product name/CAS/catalog number” on the Aladdin official website.

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