The Role of Cutaneous Microbiota Harmony in Maintaining a Functional Skin Barrier

January 2017 | Volume 16 | Issue 1 | Original Article | 12 | Copyright © January 2017


Hilary E. Baldwin MD,a Neal D. Bhatia MD,b Adam Friedman MD,c Richard Martin Eng,d and Sophie Seité PhD e

a The Acne Treatment and Research Center, Morristown, NJ bTherapeutics Clinical Research Inc., San Diego, CA cGeorge Washington School of Medicine and Health Sciences,Washington, DC dL’Oréal Research and Innovation,Tours, France eLa Roche-Posay Dermatological Laboratories, Asnières, France

Table1Skin microbiota can affect skin barrier function via bacterial enzymes, such as proteases, that may impact corneocyte des- quamation or lipases that may break down skin surface lipids (Table 1).10 Colonization by pathogenic bacteria may play a significant role in the breakdown of the skin barrier in patients with skin diseases.45 S. aureus colonization on the skin is found in up to 90% of patients with atopic dermatitis.46 This organism pro- duces ceramidase, which breaks down ceramides, an essential component of the skin barrier.47,48 The Importance of Maintaining Bacterial Diversity Changes in the normal composition of the skin microbiota can contribute to the development of in ammation. In patients with in ammatory skin disorders, increasing disease severity correlates with decreased microbial diversity overall and an elevated prevalence of Staphylococci, including both S. epidermidis and S. aureus. Several skin disorders (eg, atopic dermatitis and pso- riasis) are characterized by shifts in the skin microbiota, most notably loss of protective bacteria and outgrowth of patho- genic organisms.5,49,50 This shift has the potential to contribute to chronic in ammation. For example, S. aureus-associated molecular patterns bind to TLR2 to initiate long-lasting cutane- ous in ammation driven byT helper cells.51 MOISTURIZERS FOR MAINTENANCE OF THE SKIN BARRIER AND A NORMAL SKIN MICROBIOTA Maintaining the normal, highly diverse skin microbiota appears to be important for skin health, and moisturizers may help to maintain this diversity.52 Moisturizer modifies the water activity of the skin and so changes the growth of a wide range of bac- teria with the potential to compete with potentially pathogenic organisms.53,54 Actions of Moisturizers Moisturizers bind water to the stratum corneum, improving the skin surface hydration. This has been shown repeatedly to improve the epidermal barrier function and reduce stinging, scaling, redness, and cracks associated with xerosis.55 "To moisturize" does not only mean providing moisture, it also signi es preventing moisture evaporation from the skin. Moisturizers can be formulated with emollient, humectant, moisturizing, or occlusive agents; and some formulations have potential prebiotic activity since they may provide food for the skin microbiota.56 Emollient agents also make the skin softer and more pliable by lling the space between corneo- cytes and restoring the physical barrier function. Humectants or moisturizing agents are water-soluble substances that help the stratum corneum capture water and rebalance the cutaneous hydrolipidic lm. Occlusive agents create a sealed barrier and prevent moisture evaporation from the surface of the epidermis. Moisturizers may also have anti-inflammatory properties that potentially impact the skin microbiota since in ammation has been associated with dysbiosis.57,58 Formulation of Skin Care Products An important focus for the development of skin care products is maintaining an ecological balance in each skin niche.59,58,5 Classical moisturizers are able to protect the skin, but new-generation