Skin Barrier Function: Structure, Disorders and Care

What Is the Skin Barrier Function?

The skin barrier function refers to the ability of the skin to shield the body from the external environment while maintaining internal balance. The skin is the largest organ of the human body and serves as a vital protective layer. The barrier function prevents excessive water loss from the body and simultaneously protects against the penetration of bacteria, viruses, allergens, pollutants, and UV radiation.

The barrier consists of multiple layers and components that work together: the outermost layer of the skin (stratum corneum), the skin lipid film (hydrolipid film), the lipids between skin cells, and specialized proteins such as filaggrin, which is essential for the structural integrity of the stratum corneum.

Structure of the Skin Barrier

The skin barrier is often compared to a brick-and-mortar wall, where the dead skin cells (corneocytes) represent the bricks and the lipids act as the mortar holding everything together. This so-called brick-and-mortar model illustrates how closely the structural components are interconnected.

• Stratum corneum: The outermost layer of the epidermis, composed of dead, keratin-rich cells.
• Intercellular lipids: A mixture of ceramides, cholesterol, and fatty acids that seal the stratum corneum.
• Hydrolipid film: A thin film of sebum and sweat on the skin surface that stabilizes the natural, slightly acidic pH of the skin (pH 4.5-5.5).
• Natural moisturizing factor (NMF): Water-attracting molecules within the corneocytes that bind moisture in the skin.

Functions of the Skin Barrier

The skin barrier performs several critical protective functions:

• Prevention of transepidermal water loss (TEWL): The barrier prevents excessive evaporation of water from the body and keeps the skin hydrated.
• Defense against pathogens: The acidic pH and hydrolipid film inhibit the growth of harmful bacteria and fungi.
• Protection from allergens and pollutants: The intact lipid layer prevents foreign substances from penetrating the skin and triggering allergic or irritant reactions.
• Immunological function: The skin contains specialized immune cells (e.g., Langerhans cells) that recognize invaders and initiate an immune response.
• Protection from mechanical stress: The skin protects underlying tissue from pressure, friction, and injury.

Causes of a Compromised Skin Barrier

A disrupted skin barrier function can result from many internal and external factors:

• Genetic predisposition, e.g., mutations in the filaggrin gene (commonly associated with atopic dermatitis)
• Excessive washing or cleansing with harsh detergents
• Dry air, cold temperatures, or intense UV exposure
• Chronic skin conditions such as eczema, psoriasis, or rosacea
• Aging (the skin barrier becomes thinner and less effective over time)
• Nutritional deficiencies, e.g., lack of essential fatty acids, zinc, or vitamin A
• Stress and hormonal changes

Symptoms of a Weakened Skin Barrier

When the skin barrier is not functioning properly, the following symptoms may occur:

• Dry, rough, or flaky skin
• Redness and inflammation
• Itching and burning sensations
• Increased sensitivity to cosmetics and environmental factors
• Frequent skin infections
• Eczema and allergic reactions

Diagnosis

The function of the skin barrier can be assessed using various methods:

• Measurement of transepidermal water loss (TEWL): Specialized devices measure how much water is lost through the skin. Elevated TEWL indicates a compromised barrier.
• Corneometry: Measurement of the moisture content of the stratum corneum.
• Skin pH measurement: Deviations from the normal pH range can indicate barrier dysfunction.
• Dermatological examination: Visual assessment by a dermatologist, possibly supplemented by a biopsy.

Treatment and Care

Restoring and strengthening the skin barrier is a central goal of modern dermatology and skincare:

Topical Skincare Measures

• Use of emollients (moisturizing products) containing ceramides, fatty acids, and glycerin
• Use gentle, pH-neutral or slightly acidic cleansing products
• Regular application of moisturizers, especially after bathing or showering
• Avoid excessively hot water when washing

Medical Treatment

• For inflammatory conditions such as atopic dermatitis: corticosteroids, calcineurin inhibitors, or modern biologics (e.g., dupilumab)
• Antihistamines for severe itching
• Phototherapy for chronic skin conditions

Nutrition and Supplementation

• Adequate intake of essential fatty acids (omega-3 and omega-6) to support skin lipid production
• Zinc supports wound healing and skin regeneration
• Vitamins A, C, and E are important for cell structure and antioxidant protection
• Sufficient fluid intake to support skin hydration

References

1. Elias PM. - Skin barrier function. - Dermatologic Therapy, 2009;22 Suppl 1:S1-5. PMID: 19580575.
2. Proksch E, Brandner JM, Jensen JM. - The skin: an indispensable barrier. - Experimental Dermatology, 2008;17(12):1063-1072.
3. National Eczema Association. - Understanding the Skin Barrier. - www.nationaleczema.org