Our skin, its barrier and trans epidermal water loss (TEWL)

Our skin is our largest organ and consists of as much as 70% water. It is our barrier and this barrier (plus the person behind it) benefits from staying good and strong for as long as possible. The barrier can become weaker under the influence of UV radiation, free radicals and from bad ingredients from certain skin care and cosmetics.

A few facts:

It is helpful to understand how our skin functions as a barrier. Thus, it is important to understand the different skin layers and cells found in the skin. Our skin is composed of three layers: the epidermis, the dermis and the subcutis. For the penetration and permeability of ingredients, the first two are important.

The outer layer, the epidermis (epidermis), is separated from the dermis by a thin basal membrane. The epidermis, also called the epidermis, consists of up to five skin layers and comprises 5% of the entire thickness of the skin. From bottom to top, these are: the stratum basal, stratum spinosum, stratum granulosum, stratum lucidum and the stratum corneum (the stratum corneum). The average thickness of the epidermis varies greatly by location and averages 0.2 mm. The epidermis is rich in cells. Most cells (95%) are keratinocytes, followed by melanocytes (responsible for all processes of pigment) and Langerhans cells (part of immune system).

A keratinocyte is a very important cell. When applying and absorbing products, every ingredient at some point encounters a keratinocyte. So it can be said that these cells play a key role.

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Structure of our skin

The cells and structures responsible for the skin barrier are the keratinocytes, lipids (ceramides/skin fats), water and proteins.

The top layer of the skin can be thought of as a brick wall, with the corneocytes (the keratinocytes that have migrated to the stratum corneum) being the bricks and the lipids being the cement.

It takes both good bricks and good cement to make it solid. Sounds logical anyway.

The cement between the bricks is the most important thing. When using the right ingredients, this cement can be “replenished. Both corneocytes (bricks) and lipids (the cement) are, of course, indispensable. With a reduced barrier, such as eczema or aging skin, the number of lipids decreases. With the right ingredients, the production of lipids, such as ceramides, can be stimulated. It is then important to use a product that does not damage the skin barrier and improves the skin barrier by replenishing lipids and other important structures.

All cells in the epidermis are connected to each other and when these connections “loosen” exfoliation takes place. When the exfoliation process does not occur properly, it leads to a reduced barrier function of the stratum corneum and the entire skin. The epidermis plays a crucial role when it comes to the skin barrier and the penetration and permeability of ingredients. So this is where it all happens, both with regard to the proper absorption of ingredients but also to prevent transepidermal water loss (TEWL) from the skin.

So what exactly is transepidermal water loss?

Who does not know the image of dry lines, a tight feeling and crackling. Dry skin is partly due to a disrupted barrier and trans epidermal water loss (TEWL). TEWL is the natural, passive way the skin loses about half a liter of water per day. Not to be confused with sweating and sebum secretion, this has another cause.

The ceramides in the skin (the cement) are responsible for retaining water and preventing trans epidermal water loss (TEWL). This is possible if each element of the cement is present in the right place and in the right amount. A small change in the ratios of lipids in the skin barrier can cause an increase in TEWL and thus moisture loss. Low levels of ceramides occur in people with eczema and aging skin, i.e., with a dysfunctional skin barrier. But environmental changes such as cold weather or low humidity can also cause a decrease in these essential lipids. A reduced barrier affects the proper penetration of ingredients plus there are ingredients that can affect these essential lipids both negatively and positively.


Dry skin is caused by a lack of:

  • Natural moisturizing factors (such as urea, amino acids and lactic acid) that help bind water.
  • Upper skin lipids such as ceramides, fatty acids and cholesterol that are needed for healthy skin barrier function.

Everything impacts each other:

Deficiency of lipids and proteins: TEWL increases: moisture deficiency occurs: skin can no longer function properly -> Cell division and exfoliation do not proceed optimally, skin cells are less able to seal the skin: moisture deficiency further increases and barrier further decreases.

With a reduced barrier, more inflammatory signaling substances are released: an inflammatory reaction means reduced barrier function and a reduced barrier function, on the other hand, causes an increase in inflammatory reactions: a vicious circle!

What to do?


Skin needs nourishment in the form of active ingredients in skincare.

Ingredients that compensate for the skin’s natural lipid deficiency and strengthen the skin’s structure, by improving the attraction of the cells in the cement, thus preventing water loss and alteration of the skin (e.g. vegetable oils rich in essential fatty acids – Macademia, Pomegranate, Squalane, Triglycerides, supply of Lipid components of the epidermis).

9 Skincare Essential Serum prevents transepidermal moisture loss and does not borrow moisture from the deeper layers of the skin, but rather conditions and locks in moisture.

Essential Serum made from 100% essential oils.
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