The stratum corneum (SC) consists of corneocytes and intercellular lipids such as ceramides (40%), cholesterol (25%) and free fatty acids (10%). This lipid mixture is vital to maintaining barrier integrity. The SC is also known as the permeability barrier and moisture barrier and is responsible for ensuring essential water and electrolytes do not evaporate from skin. A lack of protection by the skin barrier means that substances like irritants, allergens and bacteria can find their way in, leading to itching, infection, inflammation and further breakdown of the protective barrier. The brick and mortar model of the SC created by Dr. Peter Elias explains how efficiently the skin prevents outside agents from penetrating and the moisture contained in the deeper layers from evaporating. It is referred to by dermatologists as the “barrier function of the skin,” but it functions as a very selective barrier.

Elias determined that the skin’s ability to resist permeation is not related to the thickness of the skin but rather the amount of lipids present in the skin. The dermatologist also postulated that there is a direct correlation between desquamation of the SC and amount of cholesterol sulfate in the stratum corneum and the intercellular cement that contains keratin and lipids. These materials provide mechanical protection and the permeability barrier to the skin.

Phospholipids, cholesterol and glycolipids contribute to healthy skin. They are responsible for binding water between the cells of the epidermis, helping the skin look smooth and firm and maintaining its health. These lipids prevent transepidermal water loss (TEWL). Their absence dehydrates the skin surface which leads to irritation or skin inflammation. The skin barrier prevents irritants from entering the skin. Cold weather and lack of humidity are common culprits for barrier damage. Damage is also caused by ingredients such as solvents, surfactants, foaming cleansers and bubble baths; mechanical influences such as stripping or abrasion; and the loss of ceramides and cell cohesion.

A fixation on cleanliness is ingrained in all of us at a young age, but “squeaky clean” is not a sign of health. Skin tightness, according to Dr. Zoe Draelos, is not related to cleanliness, but to skin barrier damage. Our obsession with that feeling is disrupting and destroying our skin’s barrier, according to Whitney Bowe MD, a New York City dermatologist and author of “Dirty Looks.”

This column reviews the skin barrier and how to keep it healthy. It serves as a protective shield against harmful microorganisms by producing antimicrobial peptides and proteins. Once the invading microorganisms are brought under control, the skin proceeds to heal itself.

The Benefits of NMF

When the skin barrier is healthy, skin is smooth, clear, even toned and balanced. If it is damaged, skin is red, irritated and prone to breakouts and other symptoms. If the waxy lipid bilayer is stripped away, skin is dull and lifeless. Moisture is not locked in, and the skin will become dehydrated and prone to fine lines. It is typically seen as redness of the skin. Most people experience uncomfortable symptoms because they have damaged their skin barrier. Skin dries out in winter and is made worse with forced air indoor heating. Cleansing habits also contribute to dry skin by disrupting skin’s natural moisturizing factor, which attracts and binds water in order to maintain moisture homeostasis in the stratum corneum. With age, various components of the NMF, such as amino acids, urea and lactic acid, decline.

As one ages, the SC loses lipids and acidity. These changes reduce the desquamation rate of keratinocytes, leading to scaling and dryness. Moisturizing cleansers help mitigate these changes, according to Dr. Andrew Alexis, a New York City dermatologist. This view is supported by Dr. John Kuleza of Young Pharmaceuticals who suggests that this not only leads to a reduction in water content, but slows the rate of exfoliation of dead cells from the skin’s surface and creates a buildup of dead cells causing a rough texture and dull appearance.

According to Alexis, cleansing is a delicate balance between removing what we don’t want and leaving behind what we do want. While it is important to remove pathogens from the skin’s surface, soaps and other cleansers remove natural lipids and oils, resulting in dryness. Soaps made with long chain fatty acid alkali salts with a high pH disrupt the skin barrier by stripping many of its natural lipids and increasing skin surface pH, which causes further barrier disruption.

In contrast, synthetic detergents used in moisturizing body washes and soaps are significantly less disruptive. The most preferred synthetic detergent is sodium cocoyl isothionate (SCI) and glycinate. Certain detergents in cleansers, such as sodium lauryl sulfate, may deplete NMF.

According to Joel Cohen MD, director of AboutSkin Dermatology & DermSurgery in Colorado, some ingredients including solvents like propylene glycol and preservatives like isothiazolinones, also deplete the NMF. Consumers with skin diseases such as acne, rosacea or atopic dermatitis may have lower ceramide levels in their skin, which decreases its water-binding capacity. Sometimes, cleansers like salicylic acid or benzoyl peroxide can dry and irritate skin.

Occlusion Is Critical

Occlusive ingredients are critical for people with atopic dermatitis. Humectants like urea improve elasticity and skin barrier function. All ingredients that can improve the NMF can also improve atopic dermatitis. With age, the skin barrier function naturally weakens. Emotional, environmental and physical stress, smoking, pollution, over-exfoliation, sensitizing ingredients, cosmetic procedures, sun damage, dehydrating beverages and poor nutrition, add to the assault on the skin. The best ways to restore skin barrier are incorporating treatments that contain ceramides and/or glycerin, both of which improve the skin barrier function by restoring and sustaining moisture.

Topical moisturizers help return skin to a healthier, more youthful state. The right combination of moisturizing ingredients must be used. Hygroscopic ingredients such as glycerin, urea, hyaluronic acid and hydrophobic ingredients such as petrolatum, mineral oil, squalene and other lipids that form a film on the skin’s surface boost barrier repair.

According to Dr. Tess Mauricoio, any moisturizer that increases skin hydration will help repair and protect the skin barrier. Occlusive moisturizers like Aquaphor, as well as humectants such as urea and sodium lactylate, help, although both humectants, and occlusive provide only temporary results. Ideal barrier repair ingredients include Phosphatidylcholine from lecithin, ceramides, triglycerides from coconut oil and squalene from olives.

Barrier Repair Products

Too many creams, serums and other hope-in-a-jar products are to blame for barrier failure, according to an article in The New York Times.¹ Or, Dr. Bowe suggests, its “largely a product of our own obsession with squeaky clean, and using product upon product upon product.” Combine product overload with environmental assaults and you have a recipe for skin barrier disaster.

According to Dr. Christian Surbar of Zurich University, who has authored a book on skin’s acid mantle, one should avoid skin care products with a pH of more than 7. This does not mean that lower the pH the better. The acid mantle of a healthy complexion has a pH of 4 to 5.5 and the ability to tolerate more acid depends on both your skin, and how well the product is formulated.

Skin grows more alkaline with age, activating enzymes that chew away at collagen. Acidic products can restore pH, protect against droopy skin and the development of wrinkles. Initially there was a lot of excitement among doctors about ceramides which glue the barrier back together and help prevent the skin from drying out and wrinkling, but the skin is simply too complex for any single ingredient to do the job, according to Dr. Stanley Tyler Hollmig, an assistant professor of surgery at Stanford University. He still recommends ceramides, but they are not a cure-all.

For barrier repair benefit, consumers should use skin care products formulated with fatty acids such as stearic or palmitic acid, cholesterol and ceramides. The most preferred humectants include glycerin, propylene glycol, urea, AHA, BHA, shea butter, lactic acid and hyaluronic acid. The most preferred occlusive agents are petrolatum and shea butter.

Hollmig notes that not all fatty acids repair the skin barrier. In fact, oleic acid, the fatty acid found in olive oil, can cause tiny holes in the skin barrier. To keep complexions hydrated and supple, choose formulas with fatty acids and phytosterols derived from evening primrose, borage and shea butter. Skin hydration and barrier function are essential to skin health and appearance. Beautiful, glowing skin is only possible when the barrier is strong and nurtured.  

Reference
1. C. Rubin, The New York Times, “All of Those Products Are Making Your Skin Worse,” July 30, 2019.

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Navin M. Geria
Chief Scientific Officer
AyurDerm Technologies, LLC
navin@AyurDerm.com

Navin Geria, former Pfizer Research Fellow is a cosmetic and pharmaceutical product development chemist and the chief scientific officer of AyurDerm Technologies LLC, which provides Ayurvedic, natural and cosmeceutical custom formulation development and consulting services to the spa-wellness-dermatology industries. He has launched dozens of cosmeceutical and ayurvedic anti-aging products. Geria has more than 30 years of experience in the personal care industry and was previously with Clairol, Warner-Lambert, Schick-Energizer, Bristol-Myers and Spa Dermaceuticals. He has nearly 20 US patents and has been published extensively. Geria edited the “Handbook of Skin-Aging Theories for Cosmetic Formulation Development” focus book published in April 2016 by Harry’s Cosmeticology. He is a speaker, moderator and chairman at cosmetic industry events. Most recently, he is author of the soon-to-be-released “Aging Well: Advances & Treatments” published by Chemical Publishing Company.