Similarly, we can use antioxidants, moisturizers, peptides, and sun protection on skin. The skin’s barrier function comes from its outermost epidermal skin layer, the stratum corneum, which offers the body a waterproof seal, keeping air out and moisture within, so the cells stay plump with fluid. Without a skin barrier, we would either become soggy from absorbing water while bathing or swimming, or shrivel up from the loss of water to the air through evaporation.

The Stratum Corneum
The stratum corneum or surface of skin contains about 25 layers of dead skin cells and is approximately 15 to 150 microns thick or the thickness of a human hair. While the stratum corneum is relatively thin, it is also very tough. Its resilience is primarily because of its keratin protein composition, which is resistant to water and many chemicals.
The structure of the stratum corneum is often explained with the “brick and mortar” model: the cells are the bricks; the lipids surrounding them make up the mortar. The stratum corneumis keratinized corneocytes, lipids, and natural moisturizing factors work together to provide an efficient barrier against water loss and promote hydration, which preserves the lower epidermal and dermal layers of skin to maintain skinís flexibility and function. When lipids are lost, the spaces between the cells dry out producing tiny breaks in the surface of the skin. These breaks allow irritants or pathogens to enter and there is an increase in trans epidermal water loss (TEWL). As this happens, tiny cracks and fine lines will begin to appear, skin dries out and becomes rough, and there is accelerated aging.

Skin Barrier and Immunity
The skin barrier is one of the most crucial parts of the immunity response. As structural changes occur in the skin because of aging and excessive sun exposure, cutaneous functions such as protection, secretion, absorption, and thermoregulation are detrimentally affected by as much as 60 percent, and skin barrier function becomes impaired.
At any given time, the skin contains approximately 50 million individual bacteria on the surface of one square inch of human skin. A healthy skin barrier supports its own ecosystems of microorganisms including yeast and bacteria, which cannot be removed by any amount of cleansing. Knowing this, it becomes clear that the stratum corneum must be diligently cared for. An unhealthy skin barrier cannot maintain the natural balance of bacteria and yeast normally found on skin, so it will become compromised and overrun by bacterial and yeast growth.
Sun protection and avoidance is very important for the skin barrier to function properly. When the sun burns skin, its immune cells (the Langerhans’ cells) become less effective and depleted. In fact, Langerhans cells are nearly completely wiped out within 24 hours after a sunburn. Exposure to ultraviolet radiation triggers an array of cellular defenses under the skin. UVB rays attack the living cells of the epidermis. The UVA rays, which are longer and penetrate deeper, attack the structures within the dermis and the epidermis. The side effect of this biological strategy is that the cells of the blood vessels become larger and the walls become thinner. Water from the bloodstream leaks through them and into the surrounding tissue causing swelling within the hour. The cells of the blood vessel walls also release inflammatory proteins, cytokines, to heal the area, but despite all of these efforts, there is cell death and destruction and the lipids of the skin cell walls are being destroyed. As a result, the stratum corneum dries out, becomes compromised, and blisters may appear.

Topical Treatment
There are a myriad of ways to strengthen and fortify the skin’s barrier function. From a topical perspective, the skin must be gently exfoliated to remove dead skin cells, but must not be stripped of its essential lipids. Alpha hydroxy acids function well to prepare the skin to accept moisturizing ingredients and nutrients such as antioxidants as AHAs work between the cells to loosen and exfoliate away dead skin cells. Retinoids can also be used to regulate the overproduction of dead skin cells and they have the added benefit of reducing inflammation over time. Papaya extract offers gentle exfoliation as well and may be appropriate for more sensitive skin types.
A key to preserving the barrier function is to stave off free radical damage caused by environmental assault. This can be done with sunscreen and antioxidants like vitamin C. Vitamin C prevents water loss and therefore maintains the skin’s barrier function. There is also increasing evidence that vitamin C shields the skin from the sun’s burning rays, especially when it is applied in high concentrations or combined with vitamin E, sunscreens, and skin soothers. The best source of vitamin C is goji berries, which contain 500 times more vitamin C by weight than oranges. Other powerful antioxidant sources include pomegranate, green tea, and durian extract.
As a final step, skin must be conditioned with humectant ingredients. To combat this weakening of the skin barrier, apricot, evening primrose, and borage seed oils may be used to increase moisture retention. Hydrophobic agents such as ceramides, prevent water loss from all cells while hydrophilic agents such as sodium PCA and hyaluronic acid attract water to the skin.
It’s important to note that as women age, their estrogen levels decline, which leads to hormonally aging skin. Estrogen helps skin maintain moisture as it increases mucopolysaccharides and hyaluronic acid in the skin, both of which contribute to maintaining stratum corneum barrier function. Hormonally aging skin responds well to regular exfoliation followed by application of humectants and plant-derived lipids to maintain a vital barrier.

Internal Treatment
To strengthen the skin barrier from the inside out, a diet rich in essential nutrients will do much to enhance hydration and prevent cell damage. A few of the most powerful nutrients with regard to the skin’s barrier include essential fatty acids, lecithin, quercetin, and zinc.
Essential fatty acids (EFAs) are found in cell membranes where they offer protection and prevent intracellular water from escaping, thus optimizing cellular functions. As such, in stratum corneum skin cells, EFAs play a role in maintaining the immune system. EFAs help increase the activity of phagocytes and are vital for preserving healthy cell membranes. Sources include coldwater fish such as mackerel, tuna or salmon, avocados, olive oil, flaxseeds, and walnuts. It is recommended to take at least 2.2 to 4.4 grams of alpha linoleic acid (omega-3 fatty acid) per day in supplement form.
Lecithin is a vital component to any wellness and skin rejuvenation program. Main sources for lecithin include eggs and soy foods. Lecithin repairs tissues as it fills in and rebuilds cell walls. It is mainly comprised of phosphatidylcholine, which is a major component of cellular membranes. A lecithin supplement (2000 mg to 4000 mg) should be taken every day.
Quercetin is a bioflavonoid known for its antioxidant and anti-inflammatory benefits. Quercetin helps inhibit the manufacture and release of histamine and is often referred to as an anti-allergy nutrient. Eating a diet rich in apples, onions, red grapes, citrus fruits, cherries, raspberries, cranberries, and broccoli helps to provide quercetin, or a dietary supplement of one gram per day supports daily nutrition.
Zinc is a valuable mineral that helps increase the production of white blood cells to fight infection. Zinc may be obtained in lozenges, dietary supplements, and through food. The goal is to aim for 15 to 25 mg per day of zinc. Foods rich in zinc include beans, nuts, whole grains, oysters, beef, and dark meat turkey. Also, many whole grain cereals are fortified with zinc.

Emotional Treatment
Skin does more than present one’s “face” to the world; it plays a vital role in the maintenance of physical and mental health. The skin and the body are connected through an elaborate relationship: the neuro-immuno-cutaneous-endocrine network (N.I.C.E.). To illustrate, a simple example of the N.I.C.E. network in action is blushing. When we feel embarrassed, our skin reacts with flushing. Dermatologists have long recognized neuropsychological connections between the appearance of the skin, perception of beauty, and health. Anxiety and cultural stressors trigger cellular water loss through perspiration and the skin may flare up with acne or eczema during stressful situations. As such, relaxation services will do much to soothe your clients and their skin, preserving the skin’s barrier—nature’s way of sealing us off for our own protection.

Howard Murad, M.D., FAAD, is recognized as one of the world’s foremost authorities on skin health. A board-certified dermatologist, pharmacist, and Associate Clinical Professor of Medicine at UCLA, Dr. Murad oversees the Murad Inclusive Health® Center and Spa, Murad Medical Group, and an active clinical research laboratory. He is a practicing dermatologist, author of two successful books; Wrinkle-Free Forever and The Cellulite Solution, and is the CEO and founder of Murad, Inc. For more information, visit www.murad.com or call 800-336-8723