Supporting Skin Structure & Its Barrier Functions With Evidence-Based Skin Care Ingredients

Medically reviewed by Dr. Adam J. Friedman. Professor and Chair of Dermatology, George Washington School of Medicine and Health Sciences, Washington, DC

The epidermis—and in particular its outermost layer, the stratum corneum—contributes much of the barrier function of the skin and is a readily visible representation of skin health (Marieb 2019). Maintaining the health of the skin barrier has arguably become more important than ever in the modern world, in which a large majority of people are exposed to environmental chemicals (Quinovic 2021; CDC 2021). These external factors can damage the integrity of the skin barrier and promote premature aging of the skin (Roberts 2021; Schachner 2023). Thus, maintaining and protecting the stratum corneum has become increasingly important.
Here, we briefly review the complex, multilayered structure of the skin and relate it to clinically translatable function, with an emphasis on the stratum corneum. In the context of epidermal structure and function, the formulation and clinical data for Phelityl® Reviving Cream will be reviewed.

Skin Homeostasis: A Brief Review of Skin Barrier Structure and Function

The functionality of the epidermis extends far beyond simply forming an interface between the body and the environment, with roles in sensation, maintaining water content, defending against and responding to infection, photoprotection, and responding to and ameliorating oxidative stress, along with crucial regulatory, metabolic, and excretory functions (Lopez-Ojeda 2022). Among all of the body’s organs, the skin is the first point of contact and is most exposed to environmental insult from microorganisms, physical injury, temperature extremes, chemical pollution, and ultraviolet (UV) light. Its remarkable ability to self-repair is an essential element of healthy skin function for people of all ages, and progressive compromise of the skin barrier is common as individuals age, as well as in patients with dermatologic and certain systemic disorders (Roberts 2021).

The most superficial layer of the epidermis—and the one that is largely responsible for the appearance of the skin to the observer and the main contributor to the skin barrier function—is the stratum corneum (Marieb 2019) (Figure 1). Only 10 to 20 µm thick, (Sandby-Møller 2003), the stratum corneum is composed of up to 30 layers of metabolically inactive, keratin-filled corneocytes that are shed at a rate approaching 50,000 cells per minute (Marieb 2019). The spaces between these cells are filled with a lipid-laden extracellular matrix. Far from being just a dead, dry layer, the healthy stratum corneum also contains about 20% to 25% water under average conditions, with water content changing dynamically in response to the humidity of the environment and the use of topical products (Murthy 2010).

Figure 1.Epidermal Structure

Focus on the Stratum Corneum

The stratum corneum has a “brick-and-mortar” composition, with the corneocytes forming the bricks and the extracellular matrix forming the mortar (Figure 2) (Kim 2020). The corneocytes are connected by corneodesmosomes that contribute to its resistance to mechanical stressors and selective permeability (Kim 2020). It is primarily composed of protein (75%-80%) and is rich in a variety of lipids that provide structural support and act as a barrier (Knox 2021). The extracellular space is a mixture of ceramides, cholesterol, and non-esterified fatty acids in approximately a 3:1:1 ratio (Knox 2021; Del Rosso 2011). Collectively, the relative composition of these lipids is critical for maintaining skin hydration and regulating transepidermal water loss (TEWL) (Del Rosso 2011).
Figure 2. "Brick-and-Mortar" Structure of the Stratum Corneum (Harding 2004)

Ceramides constitute about half of the stratum corneum lipids (Knox 2021). These molecules consist of an amino acid–containing sphingoid base linked to a hydrophobic fatty acid chain (Knox 2021). They play a critical role not only in forming the lamellar barrier of the skin, maintaining skin moisture, and preventing ingress of microbes, but also act intracellularly as second messengers for a broad range of processes (Cha 2016). Cholesterol constitutes about one-quarter of lipids in the stratum corneum (Knox 2021). It maintains the fluidity and rigidity of cell membranes and is, along with ceramides, critical for the barrier function of the stratum corneum (Knox 2021). Fatty acids, most but not all of which are synthesized de novo by keratinocytes, comprise an additional 10% to 15% of the stratum corneum lipid content (Del Rosso 2011; Khynykin 2011). These compounds are known to modulate skin-surface pH, helping it maintain its natural acidity, and to contribute to the regulation of permeability, the antimicrobial properties of the skin, and the inflammatory response (Khynykin 2011). In addition to the fatty acids synthesized by keratinocytes, the essential fatty acids (EFAs) linoleic acid and α-linolenic acid are critical elements of both the epidermis and dermis. These essential compounds are unique among the fatty acids in that they must be supplied by the diet or exogenously by topical application and are the parent compounds for more than 30 derivatives that are critical for healthy skin, as illustrated by early studies showing that deficiencies manifest as dermatitis and increased TEWL (Prottey 1975; Hansen 1958)

Along with ceramides, fatty acids, and cholesterol, the stratum corneum contains natural moisturizing factor, 
which is a mixture of small, water-soluble compounds derived from filaggrin, sweat constituents, and triglyceride turnover in the sebaceous glands (Gunnarsson 2021). These compounds make up approximately 10% of the dry weight of corneocytes and include a range of amino acids and amino acid derivatives, including pyrrolidone carboxylic acid, urocanic acid, lactic acid, sugars, urea, glycerol, and various ions (Gunnarsson 2021).

Lipids supplied by the sebum—produced by sebaceous glands—are also present on the skin surface. Sebum consists of squalene, triacylglycerols, and wax esters and is present at the highest levels on the forehead, upper chest, and upper back (Knox 2021). Squalene, an intermediate in cholesterol biosynthesis, is a particularly potent natural emollient that is efficiently absorbed deep into the skin, maintaining its suppleness and flexibility (Huang 2009). Squalene also has a protective role, quickly neutralizing free radicals and protecting the skin against oxidative damage (Huang 2009).

Normal Functions of the Stratum Corneum

The main functions of the stratum corneum include providing a selectively permeable barrier, protecting against UV light, serving as the first line of defense against pathogens and initiating the immune response to these microorganisms, quenching free radicals, and serving as a home for a diverse array of commensal skin microbiota.

Barrier and homeostatic functions: The most commonly understood function of the skin is to act as a selectively permeable physical barrier between the
internal and external environment. The multiple layers of corneocytes that comprise the bricks of the stratum corneum, together with the glycolipids that serve as the mortar, maintain proper cutaneous water balance by preventing excess TEWL (Woodby 2020). Healthy skin is critical for maintaining body temperature to avoid uncontrolled water and solute loss (Marieb 2019).

Photoprotection: The skin barrier is the primary site of exposure to UV radiation, and solar UV radiation (primarily UVA and UVB) is the primary driver of skin photoaging (Markiewicz 2019). Damage to the skin by UV radiation can be mediated by direct absorption of radiation by nuclear DNA, causing specific mutations in the skin genome. Indirect damage also may occur as a result of UV absorption into other skin constituents, the generation of reactive oxygen species, and the resulting formation of DNA photoproducts, in addition to characteristic alterations in cellular proteins and membranes (Markiewicz 2019). The skin contains an exquisite set of enzymatic pathways to continuously repair the damage caused by UV radiation and other environmental insults. Without proper care, the skin accumulates UV damage over time, leading to manifestations ranging from benign damage (wrinkling) to cancers (Markiewicz 2019).

Antimicrobial functions: The stratum corneum is the first line of defense against many microbes and contains multiple mechanisms to prevent colonization by pathogens. It responds to those that manage to survive the harsh environment of the skin, and prime the downstream immune response. The first line of defense is the acid mantle—a pH that is maintained in healthy skin of between 5.4 and 5.9—a range that is inhospitable for many potential pathogens but is tolerated by commensal bacteria (Nguyen 2019). The skin also produces a number of antimicrobial peptides that can be present constitutively or produced in response to inflammatory stimuli (Nguyen 2019). The defensins and cathelicidins, which are produced by keratinocytes, sweat glands, and sebaceous glands, among other sites, and dermcidin, which is expressed by sebocytes, have broad bactericidal activity against microbes and also may play a role in initiating the immune response (Nguyen 2019). Certain skin lipids also have intrinsic antimicrobial activity against Staphylococcus aureus, Streptococcus pyogenes, and Propionibacterium acnes, among other bacterial species (Marieb 2019; Cartron
2014; Nguyen 2019).

Antioxidant: UV radiation, air pollution, and other environmental pollutants are well-understood to cause oxidative stress. After entering the skin as nanoparticles, air pollutants can produce reactive oxygen species that negatively impact the enzymatic and nonenzymatic activities of the skin and stimulate the release of proinflammatory mediators, among other negative effects (Roberts 2021). The skin contains an endogenous network of enzymatic and nonenzymatic systems to counter oxidative stress by quenching free radicals generated by environmental insults (Del Rosso 2011).

Host to the skin microbiota: The skin also hosts a diverse array of bacteria, fungi, and viruses that collectively compose the skin microbiota, the composition of which varies substantially depending on the local physiology of the skin (Byrd 2018). Commensals on the skin surface actively prevent colonization by pathogenic microbes; furthermore, evidence suggests that there is crosstalk between the immune system and microbiota to assist in the maintenance of the normal microbial composition of the skin and eliminate pathogens (Byrd
2018). The normal microbiota not only defends against potentially harmful microorganisms but can also produce substances that are directly beneficial for the skin. For example, data suggest that commensal Staphylococcus epidermidis produces protective ceramides that contribute to skin barrier homeostasis, and thus help to prevent skin dehydration and aging (Zheng 2022).

Importance of Maintaining the Skin Barrier

As discussed, the skin barrier is both a multifunctional structure with critical roles in defending against environmental assault and homeostasis, as well as the structure that reflects our outward appearance to the world. Many of the functions of the epidermal barrier are the responsibility of the stratum corneum; thus, maintaining the stratum corneum is a priority for overall skin health. In addition to exogenous factors, aging has been shown to compromise the integrity of the stratum corneum, with changes in its biomechanical properties including stiffening of keratin fibers, increased cellular cohesion, and decreases in water movement through the stratum corneum (Biniek 2015). Levels of all 3 major classes of skin lipids—ceramides, cholesterol, and free fatty acids—also decline significantly with age, leading to compromise of the barrier function of the skin (Rogers 1996). Furthermore, the pH of the stratum corneum tends to increase with age, which has been shown to increase serine protease activity and reduce corneodesmosome density (Choi 2007).

Several modifiable risk factors for poor skin barrier function can be readily addressed with appropriate routine skin care, including gentle cleansing and use of topical products designed to moisturize and support skin barrier function and avoiding unnecessary environmental exposure, the use of irritating topical products, and extended exposure to low-humidity environments (Del Rosso 2016). Conversely, without proper attention, the integrity of the stratum corneum can be compromised, leading to both visible and invisible manifestations such as dry, flaky skin, itching, and irritation.

Phelityl® Reviving Cream

The science underlying the structure and function of the skin barrier was carefully considered in the development of Erno Laszlo’s Phelityl® Reviving Cream. Central to the product formulation is the Phelityl® Complex, a blend of botanical substances with evidencebased benefits on skin barrier health, which was combined with other ingredients to support the skin barrier and enhance hydration.

Phelityl® Reviving Cream Key Components
  • Phelityl® Complex
    • Biobotanical blend
      • Acacia gum biopolymer
      • Plant-derived polyglycerides
      • Rosehip oil
    • Squalane
    • Ceramides
  • Red algae
  • African tree and oleanolic acid blend
  • Glycerin

Phelityl® Complex

The Phelityl® Complex is composed of a blend of botanical substances, including acacia gum biopolymers, plantderived polyglycerides, and rosehip oil, along with squalane and ceramides.

Acacia gum (also known as gum Arabic) is an exudate gum produced by the Acacia senegal tree and a primary ingredient in Phelityl® Complex. Acacia gum is among the oldest substances used by humans, with the first recorded use over 5000 years ago. In clinical studies, acacia gum was shown to improve skin barrier and hydration (Data on File).

The plant-derived polyglycerides and rosehip oil in the Phelityl® Complex each contribute EFAs to the formula. The mixture of polyglycerides is of 100% vegetable origin and includes oleic, linoleic, and linolenic fatty acids, the latter 2 of which are the parent fatty acids of the omega-6 and omega-3 series of EFAs (Linus Pauling 2024). Rosehip oil, an extract prepared from Rosa damasca, contains high amounts of essential polyunsaturated fatty acids derived from linoleic, linolenic, and arachidonic acids (Kutaitiene 2020).

Squalene is a triterpene intermediate in the cholesterol biosynthesis pathway (Huang 2009). In humans, squalene is present in the highest concentrations in the skin, where it is produced in abundance by the sebaceous glands and constitutes approximately 13% of sebum (Huang 2009). Squalane, a hydrogenated derivative of squalene, is a powerful emollient and is absorbed into the skin, where it plays an important role in maintaining the suppleness and flexibility of the skin (Huang 2009). Beyond its emollient properties, squalane, sourced from renewable sugarcane, contributes to the ability of Phelityl® Reviving Cream to limit TEWL (Huang 2009).

Finally, the Phelityl® Complex contains a ceramide blend. Ceramides are the predominant lipid in the stratum corneum and act to maintain skin moisture (Dragicevic 2015; Knox 2021).

Additional Key Constituents of Phelityl® Reviving Cream

Phelityl® Reviving Cream contains an extract from red algae (Porphyridium cruentum). The marine exopolysaccharide derived from this organism contributes to the long-lasting moisturizing properties of Phelityl® Reviving Cream, and its high molecular mass contributes to its film-forming properties, which together help to preserve and maintain skin hydration for extended periods (Data on File; Mourelle 2017; The Derm Review 2024).

In addition to red algae, Phelityl® Reviving Cream contains a blend composed of extracts from the African Tree (Enantia chlorantha) in combination with oleanolic acid. In particular, extracts from this plant have been reported to regulate sebocyte differentiation and proliferation and to mildly inhibit 5α-reductase activity in the skin, leading to a reduction in sebum secretion (Data on file). Finally, glycerin, a natural humectant, contributes to the hydration of the stratum corneum and may protect against skin irritants (Milani 2017).

Phelityl® Reviving Cream: Clinical Study Results

The effect of Phelityl® Reviving Cream on key skin parameters was evaluated in a study in which female subjects (N=31) aged 20 to 60 years who were predominantly of combination face skin type applied the product twice daily for 56 days.

The use of Phelityl® Reviving Cream was associated with statistically significant improvements in a broad range of parameters, including skin barrier (TEWL), hydration, and sebum on the skin surface, while helping maintain a physiologic acidic skin pH (Data on file, Erno Laszlo 2024). Specifically, there were statistically significant results including a decrease in TEWL (P<0.0001), an increase in hydration (P<0.0001), and a decrease in skin surface sebum (P<0.0001) compared with baseline. The skin’s acidic pH was maintained with no change throughout the study. On the forearm portion of the study for assessing hydration, when comparing treated and untreated areas, there were statistically significant increases in hydration immediately after application (P<0.0001) and after 24 hours following a single application (P<0.0001). In the subject questionnaire, 97% of the subjects reported that their skin felt hydrated after use, 90% reported that the product left a soft matte finish, and all the subjects were satisfied with the results.


Complex and multilayered, the skin performs a multitude of essential functions. The health of the stratum corneum is at considerable risk in today’s environment, with people exposed more than ever before to air pollution and environmental chemicals that can damage its structural and functional integrity (Roberts 2021; Schachner 2023). It is clear that preserving the epidermal barrier—the stratum corneum—is a priority for proper skin function and appearance. Carefully formulated topical products that have long-lasting moisturizing properties and can potentially optimize skin barrier health are an important way to support overall skin health.

Phelityl® Reviving Cream is formulated with ingredients that have synergistic benefits that, together, help strengthen the skin barrier and maintain skin hydration. The effects of Phelityl® Reviving Cream were confirmed in a study in which Phelityl® Reviving Cream was shown to be associated with improvements in both immediateand long-term parameters, including a significant positive effect on the skin barrier and immediate and long-lasting hydration. Phelityl® Reviving Cream also had a statistically significant, effect on skin-surface sebum, consistent with subject reports that the product left a soft-matte finish to their skin. Together, these results indicate that Phelityl® Reviving Cream provides important skin benefits including supporting the skin barrier and enhancing hydration, to help maintain healthy looking skin.


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