What is the skin barrier?

The skin is divided into three layers: the epidermis (the outermost layer), the dermis (the middle layer), and the hypodermis (the deepest layer). The stratum corneum is the scientific term for the skin barrier, and this is the most superficial layer of the skin, serving as a vital protective shield. 

The skin protective barrier is often compared to bricks and mortar, which presents its highly organized nature. Homeostatic preserving nature of the barrier is best described by its protective purposes as well as moisture retention function:

• Bricks (Corneocytes): The first layer of the epidermis includes flattened, non-living cells, whose composition consists largely of keratin and natural moisturizing factors (NMFs) which are regulating the water retention. Their dense and layered arrangement makes the corneocytes foundation similar to bricks in the wall that offer stability and durability to the skin barrier against external influences. 

• Mortar (Intercellular Lipids): The passageways between corneocytes are filled with intercellular lipids made of ceramides, cholesterol, and free fatty acids. This whole intercellular lipid matrix ties corneocytes into a network making a waterproof seal that minimizes transepidermal water loss as an external substance penetration, such as pollutants and pathogens.

• Hydrolipidic Film: The top of the skin has a thin layer that is emulsified in the form of water and lipids, also known as the hydrolipidic film. Sweat combines with oil secretions and water, making an additional protective film, which helps maintain pH and serves as an extra barrier against environmental aggressors.

Without a functioning skin barrier, the body would be vulnerable to external harm and lose excessive moisture, leading to dryness and irritation. The skin barrier has several following functions that are beneficial to the human body and life in general.

Defense from external aggressors.

The skin barrier protects us from outdoor aggressors such as wind, temperature extremes, and air pollution. It also shields us from dangerous microorganisms, viruses, bacteria and fungi. The corneocytes build up a wall-like barrier that doesn't allow pathogens to pass through to the interior, much like bricks set in order. Without the proper protection all of these aggressors could easily damage and irritate the skin.

Regulation of moisture levels.

This barrier also helps in retaining moisture by serving as an occlusive layer in order to reduce trans-epidermal water loss (TEWL). It also helps in maintaining skin flexibility and smoothness and gives it a generally radiant appearance.

Protection from UV radiation.

Deeper layers of the skin, such as the dermis, are primarily responsible for repairing and mitigating long-term UV damage. On the external surface, tightly packed corneocytes provide initial reflection and scattering of UV rays, reducing their impact on the skin. When combined with a healthy diet, the addition of antioxidants to the hydrolipid film provides an extra line of defence by neutralising UV-induced free radicals on the skin. 

Maintaining pH balance.

The hydrolipidic film maintains the natural pH of the skin that plays an important role in creating a slightly acidic environment. This environment will eventually develop intercellular lipids and form an intact, functional barrier. Damage or imbalance in pH disrupts the skin’s harmony, compromising its defense and making our body susceptible to bacterial and fungal infections.

The skin barrier is dynamic and has the ability to repair itself when compromised. The rehabilitation rate and success of the repair are conditioned by age, health, and other external factors. When this barrier is damaged, processes that upregulate lipid biosynthesis and reconstitute the corneocyte structure are initiated, allowing that barrier once again to perform its protective functions.

This complex structure in the architecture of the skin is essential for protection, hydration, and overall health. Barrier functions underlie the crucial importance of maintaining skin’s integrity. In addition to dermatology, scientific research will further advocate better ways to provide skin care that will support and protect this remarkable system.

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