WHAT IS THE SKIN BARRIER?

Your skin has two major layers: the outer layer- the epidermis- and an inner layer- the dermis. The technical term for the skin barrier is the stratum corneum and it is the outermost sublayer of the epidermis. This sublayer consists of keratin-rich dead cells called corneocytes which are pushed up through the five sublayers of the epidermis as they mature, releasing lipids, ceramides, growth factors, antimicrobial, and antioxidant molecules into the epidermis along the way. As these cells reach the outer most layer, they become tightly organized like a brick-and-mortar wall or barrier1. Our skin barrier functions to retain moisture while protecting us from environmental aggressors like sun damage, harmful chemicals, infections, and lacerations. It’s easy to see why nourishing our skin barrier is so important and how sometimes, it needs extra help fighting off or repairing damage. 

A healthy skin barrier contains both an extracellular lipid “sheet” referred to as the lamella and an intracellular environment rich in natural moisturizing factors (NMF). In the lamella, corneocytes are closely embedded in a lipid- and protein-rich extracellular “sheet” which contains cholesterol, fatty acids, and the secretory molecules mentioned above2. However, the intracellular composition of the corneocytes is quite different, containing NMF, a combination of amino acids, electrolytes, urea, and other hygroscopic molecules that pull moisture from the environment to maintain the delicate moisture balance3. A skin care regimen that addresses the both the strength of the lipid lamella and the moisture needs of the intracellular environment will create a healthy skin barrier that can handle every day environmental microdamage.

What we observe as damage to the skin barrier and attempt to treat with cosmeceuticals is often a result of dysfunction at multiple sublayers of the epidermis4. As mentioned above, skin damaging agents are a diverse group of physical (e.g. infections or cuts), chemical (e.g. dehydration, chemical burns, or allergic reactions), and electromagnetic (e.g. UVA and UVB radiation) insults5. Our skin barrier and additional sublayers of the epidermis perform highly coordinated signaling cascades that allow for dynamic and adaptive responses to all of these aggressors. In addition to external damage, our genes and the small variations that exist person to person determine the natural disposition of our skin and its ability to repair itself. Our unique genetic composition combined with our unique lifestyles (exposure to environmental damage) is why different products work for different people. 

Thankfully, research in the dermatology field is continuing to discover powerful ingredients that maintain and restore the functions of the skin barrier. By understanding the composition of the skin barrier and the types of damage that it incurs, you can tailor your skin care regimen to your needs with less trial-and-error. 

Sources:

1. Rosso, J. D.; Zeichner, J.; Alexis, A.; Cohen, D.; Berson, D. Understanding the Epidermal Barrier in Healthy and Compromised Skin: Clinically Relevant Information for the Dermatology Practitioner.J Clin Aesthet Dermatol 2016,9 (4 Suppl 1), S2–S8.

2. Harwood, A.; Nassereddin, A.; Krishnamurthy, K. Moisturizers. InStatPearls; StatPearls Publishing: Treasure Island (FL), 2020.

3. Sethi, A.; Kaur, T.; Malhotra, S.; Gambhir, M. Moisturizers: The Slippery Road.Indian J Dermatol 2016,61 (3), 279–287. https://doi.org/10.4103/0019-5154.182427.

4. Kanwar, A. J. Skin Barrier Function.Indian J Med Res 2018,147 (1), 117–118. https://doi.org/10.4103/0971-5916.232013.

5. Parrado, C.; Mercado-Saenz, S.; Perez-Davo, A.; Gilaberte, Y.; Gonzalez, S.; Juarranz, A. Environmental Stressors on Skin Aging. Mechanistic Insights.Front Pharmacol 2019,10. https://doi.org/10.3389/fphar.2019.00759.