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Skin Barrier Function 101

Why it matters  

Skin is the largest organ in your body. Its main role is to provide a protective barrier between your internal and external environments - this is called the skin barrier function [1]. Your skin protects you from allergens, microbes, UV radiation, and pollution. It also prevents excessive water loss to keep your skin hydrated and radiant. Thus, a healthy skin barrier is the key to achieving happy, glowing skin. Without a healthy skin barrier, the skin appears aged, dry, rough, and conditions such as xerosis, eczema, or even sensitive skin can arise.

The cycle of skin renewal

The outermost layer of the skin, known as the stratum corneum (represented by the peach-colored cells called corneocytes in the diagram below), is where your skin barrier health is put to the test: external factors, such as UV, pollution, mechanical stress, and cleansing with detergents constantly challenge your skin’s outer layer. However, healthy skin is resilient, and stands against these external irritants through constant shedding and regeneration – your skin’s outer layer is actually completely renewed every 2-3 weeks [2]! Miraculous, isn’t it?

Your skin's outer layer is actually completely renewed every 2-3 weeks. 

The renewal process starts in the deeper layers of the epidermis called the stratum basale (in red below). The stem cells in the stratum basale divide and create new cells called keratinocytes. These keratinocytes undergo a transformation as they move from one layer to another until they rise to the skin's surface, eventually becoming corneocytes. Corneocytes play an active role in your skin barrier function until they are eventually shed in your skin's renewal process, revealing a new batch of corneocytes underneath.

Healthy Skin Barrier vs Compromised Skin Barrier 

Breaking down the anatomy!

Your skin barrier has two components, the physical barrier, and the acid mantle. The physical barrier is composed of corneocytes surrounded by multilamellar lipid membranes (ceramides, fatty acids, and cholesterol [3]). The acid mantle consists of many different molecules (such as amino acids, alpha hydroxy acids, fatty acids, and other small molecules) that are released from the sweat and sebaceous glands. The physical barrier and acid mantle work together to maintain healthy skin: components of the physical barrier (such as cholesterol sulfate or fatty acids) contribute to the acidic skin surface pH and in turn, this acidic pH is required to synthesize important skin ingredients such as ceramides.

A defective skin barrier is more prone to allergen penetration and microbial infection.

All of the components of the skin barrier (corneocytes, lipids, and the acid mantle) are necessary to maintain skin barrier integrity and consequently skin health in general. Defects in the skin barrier result in excessive transepidermal water loss (TEWL) that may result in dry skin or xerosis. A defective skin barrier is also more prone to allergen penetration and microbial infection. These in turn can stimulate an immune response that results in inflammation, irritation, and itch that may further weaken the skin barrier and affect skin barrier renewal. This can create a vicious cycle, often seen in eczema.

What are the common factors that can disrupt the skin barrier?

UV and pollution UV and pollutants may induces oxidative damage to the stratum corneum. The oxidation of lipids and carbonylation of proteins induced by UV or pollution can result in barrier disruption and poor skin conditions.

Frequent cleansing – during cleansing, skin is exposed to relatively high concentrations of surfactants. Surfactants have the ability to remove your stratum corneum proteins, lipids, and natural moisturizing factor. So, don't over-cleanse! If your skin is oversensitive or dry, consider only rinsing with water in the morning. 

Traditional bar soaps – in addition to containing high concentration of surfactants, traditional soaps usually have very high pH 9+. That high pH may be harmful to your skin barrier. 

Conclusion:
In conclusion, a healthy skin barrier is critical for healthy and glowing skin. Take care of your barrier and it will take care of you! Read our article on how to protect your skin barrier.

 

References:

[1]       J. A. Bouwstra and M. Ponec, “The skin barrier in healthy and diseased state,” Biochim. Biophys. Acta - Biomembr., vol. 1758, no. 12, pp. 2080–2095, 2006, doi: https://doi.org/10.1016/j.bbamem.2006.06.021.

[2]       W. L. EPSTEIN and H. I. MAIBACH, “Cell Renewal in Human Epidermis,” Arch. Dermatol., vol. 92, no. 4, pp. 462–468, Oct. 1965, doi: 10.1001/archderm.1965.01600160118025.

[3]       K. C. Madison, “Barrier Function of the Skin: ‘La Raison d’Être’ of the Epidermis,” J. Invest. Dermatol., vol. 121, no. 2, pp. 231–241, 2003, doi: https://doi.org/10.1046/j.1523-1747.2003.12359.x.

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