The connection between the skin barrier and the rest of the body

The skin barrier is our outermost layer of protection against the surroundings. Recent research has shown that a properly functioning skin barrier is important not only for the skin, but for the whole body to be in balance.

This article is based on an interview with Professor of Dermatology, Torkil Menné.

The skin barrier is our outermost layer of protection against the surroundings. It works as a shield to protect the body’s internal environment against the many influences in our surroundings, and it prevents water evaporating from the body. A properly functioning skin barrier is essential to maintain the whole body in balance. Recent research has shown that a damaged skin barrier can lead to a chronic low-grade inflammatory response inside the body and, conversely, certain systemic immune disorders can trigger an inflammatory response outwardly in the skin, damaging the skin barrier.

The skin is the largest organ in the human body. The skin is made up of a subcutaneous layer, the dermis and the epidermis. The epidermis is made up of cell layers that are continuously renewed. Uppermost in the epidermis is the skin’s barrier against the surroundings.  If this barrier is disrupted or damaged, dry and scaly skin can result.

Structure of the Skin Barrier
The epidermis helps to form the barrier that forms our outer surface. This barrier is constructed in a pattern that resembles a wall of bricks and mortar. The “mortar” is a layer of fats called lipids. While the “bricks” are cells from the epidermis that are gradually transformed into keratin bricks. These keratin bricks are made up of protein fibrils held together by the protein filaggrin, which plays an important role in the maintenance of a normal, properly functioning skin barrier.

On the surface of the skin, these bricks and mortar are broken down. This process creates free lipids and filaggrin is broken down into amino acids. This mixture of lipids and amino acids is a key part of the skin’s Natural Moisturizing Factor (NMF).

The Natural Moisturizing Factor (NMF)
It is absolutely crucial for the skin barrier that the epidermis has a normal NMF (Natural Moisturizing Factor). Otherwise, it can lead to dryness and the formation of scales and cracks – which can eventually evolve into eczema.

A correctly functioning NMF contains water-binding substances, especially amino acids derived from filaggrin but also lactic acid, for example.

The skin’s moisturizing factor
It is absolutely crucial for the skin barrier that the epidermis has a normally functioning NMF (Natural Moisturizing Factor). Otherwise, it can lead to dryness and the formation of scales and cracks – which can eventually evolve into eczema.

The acid-base balance in the skin
It is also important for the skin barrier that there is a normal acid-base balance in the skin – that is, a pH between 5.5 and 6. A normal acid-base balance helps to ensure that the metabolic processes in the skin function normally so that lipids can be formed, etc. The amino acids – especially the amino acid histidine – are responsible for maintaining this normal acid-base balance in the skin.

Keeps chemicals out and water in
The skin is exposed to many impacts from the environment – dry weather, a dry indoor climate, chemicals in the workplace, cosmetic products for washing and caring for the skin, etc. The barrier acts as a shield that protects the skin from absorbing chemicals. A damaged skin barrier increases the risk of developing chronic eczema – especially hand eczema, also called hand dermatitis.

The barrier also ensures that water does not evaporate from the body causing the body to dehydrate. This is an important function as the body contains approx. 70% water.

Link between the barrier and the rest of the body
If the skin barrier is not functioning properly, an inflammatory response occurs throughout the skin. Recent research has shown that a damaged skin barrier can also have a more systemic effect on the body – so you not only have an inflammatory response in the skin but also get a chronic low-grade inflammatory response, which goes inward into the body. This is known as inflammaging and is associated with the development of certain age-related systemic disorders. A properly functioning skin barrier is therefore important, not only for the skin, but for the whole body to be in balance.2

The connection between the skin barrier and the rest of the body also goes the other way. The illness Sjögren’s syndrome and other similar systemic immune disorders inside the body can lead to an inflammatory response in the skin. This inflammatory response in the skin results in insufficient production of filaggrin and leads to a defective skin barrier.

Protects against allergenic substances
A correctly functioning barrier is also important to protect the skin from allergens in the surrounding environment. If you have filaggrin deficiency, you are exposed to an increased uptake of certain cosmetic products. Nickel allergy is also seen more frequently in people who suffer from a lack of filaggrin.

A damaged skin barrier must be treated
In the past, a damaged barrier was typically treated by applying a layer of fat that settled on the skin as a kind of artificial barrier. However, newer products have been developed that repair the skin barrier by adding water-binding elements in the form of amino acids, which are the building blocks of the filaggrin protein. These amino acids occur naturally in a properly functioning skin barrier.

Amino acids are important for maintaining the water-binding capacity of the epidermis and also play an important role in maintaining the normal acid-base balance in the skin. Amino acids also block allergenic metal compounds such as nickel and reduce the risk of skin infections. It has been shown that a normally functioning skin barrier built with the body’s naturally occurring amino acids reduces the risk of staphylococcal infections.

Amino acids: An important part of the skin barrier
Amino acids occur naturally in a properly functioning skin barrier. They play a key role in maintaining the skin’s water-binding ability and a normal acid-base balance in the skin. Amino acids also block allergenic metal compounds such as nickel and reduce the risk of skin infections.

Would you like to learn more?
If you would like to gain a deeper insight into the fascinating research on the structure and function of the skin barrier, you can delve into the articles listed as references below.

References:
  1. Yosipovitch G, Misery L, Proksch E, Metz M, Ständer S, Schmelz M. Skin Barrier Damage and Itch: Review of Mechanisms, Topical Management and Future Directions. Acta Derm Venereol. 2019 Dec 1;99(13):1201-1209
  2. Wang Z, Man MQ, Li T, Elias PM, Mauro TM. Aging-associated alterations in epidermal function and their clinical significance. Aging (Albany NY). 2020 Mar 27;12(6):5551-5565
  3. Howell MD, Kim BE, Gao P, Grant AV, Boguniewicz M, Debenedetto A, Schneider L, Beck LA, Barnes KC, Leung DY. Cytokine modulation of atopic dermatitis filaggrin skin expression. J Allergy Clin Immunol. 2007 Jul;120(1):150-5
  4. Angelova-Fischer I, Dapic I, Hoek AK, Jakasa I, Fischer TW, Zillikens D, Kezic S. Skin barrier integrity and natural moisturising factor levels after cumulative dermal exposure to alkaline agents in atopic dermatitis. Acta Derm Venereol. 2014 Nov;94(6):640-4
  5. Thyssen JP, Johansen JD, Linneberg A, Menné T, Nielsen NH, Meldgaard M, Szecsi PB, Stender S, Carlsen BC. The association between null mutations in the filaggrin gene and contact sensitization to nickel and other chemicals in the general population. Br J Dermatol. 2010 Jun;162(6):1278-85
  6. Fluhr JW, Elias PM, Man MQ, Hupe M, Selden C, Sundberg JP, Tschachler E, Eckhart L, Mauro TM, Feingold KR. Is the filaggrin-histidine-urocanic acid pathway essential for stratum corneum acidification? J Invest Dermatol. 2010 Aug;130(8):2141-4

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