>>Ceramides, the “back bone” of the epidermal barrier

Ceramides, the “back bone” of the epidermal barrier

The words “fats” and “lipids” conjure up negative connotations because they are often associated with problems such as obesity and atherosclerosis.
But fat is not always negative.
Quite the opposite. When it refers to the skin, “lipid” (from the Greek “lipos” which means fat) is synonymous with wellbeing. This is because some lipids actually guarantee the functionality of the skin barrier, stopping harmful substances from penetrating the inner layers of the skin and preventing excessive water evaporation.

The essential lipids of the epidermal barrier are:

  • cholesterol
  • fatty acids
  • ceramides 

What are ceramides?

Ceramides are the “back bone” of the epidermal barrier, they retain water in our body which is needed for well-balanced cells and organs.

They are lipid molecules made up of a fatty acid and sphingosine (a component of cell membranes). They are synthesised by the skin by precursors (glucosylceramides), thanks to the action of specific enzymes (ceramide synthase).

Ceramides have been the subject of extensive study in the past 20 years, but there is still a lot we do not know about them.
Around 300 different types have been identified to date in the stratum corneum, the outermost layer of the skin, but researchers believe there could be as many as over 1000.

There are so many variants because ceramides have different characteristics: the length of the fatty acid chain or the presence of a functional hydrophilic group. 
Let’s see what that means.

What are ceramides made up of?

As we mentioned before, ceramides are made up of a fatty acid and sphingosine: they develop in linear chains of different lengths which become more “extended” and connect with one another both horizontally and vertically.

These long chains can also contain a number of functional elements like hydroxyl groups (-OH) which are made up of oxygen and hydrogen and act as anchors to retain water molecules. This creates an “architecture” of lipid layers which overlap compactly until they form lamellar structures.

What do they do to protect the skin?

In this architecture, the ceramides slot in between the fatty acid and cholesterol molecules, forming a fluid and elastic intercellular “cement” which keeps the skin’s “bricks”, or corneocytes, in the proper arrangement.

This structure is achieved only if each element is in the right place and the right quantity.

Even the slightest variation in the qualitative and quantitative proportions between the lipids in the skin barrier can bring about an alteration in the general architecture of the skin, having a significant effect on its functionality, leading to an increase in transepidermal water loss (TEWL).

This explains why common skin conditions like atopic dermatitis and psoriasis are brought on by a lack of ceramides.
With atopic dermatitis and psoriasis, the skin barrier is deficient and many studies have shown that when ceramides are present and correctly conveyed in topical emollient products, they can help restore the skin’s natural balance and reduce symptoms.

Recent studies also indicate that ceramides can act as “alarms” to control skin processes: it is thought they can modulate the self-defence mechanisms of the skin and its inflammatory responses… but we’ve still got a long way to go!

 

Bibliography
  1. P.M. Elias Structure and function of the stratum corneum Extracellular matrix  Journal of Investigative Dermatology 132 (2012) , 2131-2133
  2. D.J.Moore and A.V. Rawlings The chemistry, function and (patho)physiology of stratum corneum barrier ceramides International Journal of Cosmetic Science (2017) , 1-7
  3. J.A. Bouwstra, M. Ponec  The skin barrier in healthy and diseased state Biochimica et Biophysica Acta 1758 (2006), 2080-2095
  4. M.H.Meckfessel and S.Brandt The structure, function and importance of ceramides in skin and their use as therapeutic agents in skin-care products JAAD 2014; 71:177.84
  5. J. Van Smeden, M. Janssen, G.S. Gooris, J.A. Bouwstra The important role of stratum corneum lipids for cutaneous barrier function Biochimica et Biophysica Acta 1841 (2014) 295-313
  6. Y. Uchida Ceramide signalling in mammalian epidermis Biochimica et Biophysica Acta (2014)  1841(3): 453-462
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