The skin is the largest organ in the body and provides us with an excellent barrier to protect against insults from the environment, while preserving moisture in our bodies. It is what protects our bodies against mechanical injury, low humidity, bacteria, viruses, cold, heat, sun, wind and chemical exposure. Other key functions include maintaining skin moisture/flexibility, regulating immune function, and activating the release of signaling cytokines to repair skin damage.
A healthy skin barrier is critical to normal skin function and many common dermatogical conditions are related to having an abnormal skin barrier function. These include dry skin, sensitive skin, and atopic dermatitis (Eczema).
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It is estimated that 3.1% of the US population is actively treating dry skin at any time and this figure is probably significantly higher in the winter. The incidence of dry skin is also increasing as the population is aging. Approximately 50% of females and 30% of males have sensitive skin and 35% of subjects with sensitive skin also have dry skin.
Atopic dermatitis is one of the most common skin diseases, particularly among infants and children. The estimated prevalence in the United States is 9% and it appears to be increasing. In man, the skin barrier function is provided by the outermost layer of skin called the Stratum Corneum. It is made up of 15-20 layers of flattened cells or Corneocytes, which are surrounded by epidermal lipids.
Dr. Peter Elias described the Stratum Corneum as being similar to a brick wall with the Corneocytes being the bricks and the epidermal lipids the mortar. These lipids are comprised of 40% Ceramides, 25% Cholesterol, 25% free fatty acids, and 10% Cholesteryl Sulfate.
Ceramides have been found to be the most important component in the Stratum Corneum for maintaining barrier function. The epidermal lipids represent ~15% by weight of the Stratum Corneum and are structured in lamellar lipid bilayers which exist in a liquid crystalline, hexagonal, and orthorhombic state.
This model is referred to as the Domain Mosaic Model and was first proposed by Forslind in 1994.The orthorhombic is the most crystalline phase and exhibits the lowest skin penetration and provides the best barrier to moisture loss. The ratio of hexagonal to orthorhombic lipid packing varies depending on the moisture content of skin. In normal skin both forms are present. However, in dry skin there is an increased proportion of hexagonal to orthorhombic forms.
Hexagonal packing is less effective at regulating water loss, resulting in the increased trans epidermal moisture loss (TEWL) seen in dry skin. Skin barrier function is determined by measuring TEWL normally after exposing skin to an irritant like Sodium Lauryl Sulfate, which causes an increase. A more robust skin barrier will have a lower TEWL than a damaged barrier.
Strategies for improving the skin barrier function include using humectants, barrier restoring lipids, and stimulating epidermal lipid synthesis. Other approaches include utilizing lamellar gel network-based oil in water formulations, and utilizing soothing agents to reduce skin irritation. It is well known that chronic low level skin irritation can reduce the skin barrier function and accelerate skin aging. I believe that a good barrier-protecting and restoring base formulation will improve the efficacy of any skin repair product sold.
• Glycerin-is the gold standard, numerous clinical studies have confirmed its efficacy at improving the barrier function.
• Hydrovance (Akzo-Hydroxyethyl Urea)-it has a similar moisturizing profile as Glycerin with a significantly better sensory profile. Synergism with Glycerin is also claimed.
Recommended barrier restoring lipids
• Isostearyl Isostearate (Crodamol ISIS)-has been shown to be more effective than Petrolatum in reducing TEWL. It also has a much better skin feel.
• SymRepair 100 (Hexyldecanol, Bisabolol, Cetylhydroxyproline Palmitamide, Stearic Acid, Brassica Campestris (Rapeseed) Sterols-Symrise) has been clinically shown to protect and repair skin barrier function at .2% active.
• Ceramide II (Givaudan) is identical to Ceramide II found in skin, has significant moisturizing activity when combined with sterol and fatty acid.
• Actilipid (Triticum Vulgare (Wheat) Germ Extract, Olea Europaea (Olive) Fruit Extract, Coleus ForskoCuspidatum (Japanese Bamboo) Extract, Helianthus Annuus (Sun flower) Seed Oil-Lubrizol) hlii Root Extract, Polygonum
Recommended epidermal lipid stimulants
• Niacinamide (Lonza)
• L-Lactic acid (Corbion Purac)
• Soline (sunflower non-saponifiables- Expanscience Laboratories)
Recommended lamellar gel network forming oil in water emulsion bases
• NET-LCS (Caprylic/Capric Triglyceride, Hydrogenated Lecithin, Cetyl Alcohol, Stearyl Alcohol, Behenyl Alcohol, Phytosterol, Glyceryl Stearate, PEG-20 Soya Sterol-Barnet Products)
• Crystalcast MM (Beta-Sitosterol, Sucrose Stearate, Sucrose Distearate, Cetyl Alcohol, Stearyl Alcohol-MMP)
• Biophilic H (Hydrogenated Lecithin, C12-16 Alcohols, Palmitic Acid-Lucas Meyer)
Recommended soothing agents
• D Panthenol USP (BASF Care Creations)
• SymCalmin (Butylene Glycol (and) Pentylene Glycol (and) Hydroxyphenyl Propamidobenzoic Acid-Symrise)
• Gorgonian extract BG (Butylene Glycol and Sea Whip Extract- Vantage Specialty Chemicals)
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