What is transepidermal water loss or TEWL?

Transepidermal water loss or TEWL is considered to be one of the most important parameters that help to understand and evaluate skin health and to assess its barrier function.

Being a barrier between the inside of the body and the external environment is one of the main functions of the skin but it’s not the only one: regulating water loss and stopping water to escape from the body is another main function of this barrier and for this reason the integrity and proper functioning of the skin is of utmost importance to avoid a wide range of dermatological conditions and diseases.

When the skin barrier is disrupted, we are not only at higher risk of infection, but there is also an increase in transepidermal water loss and a decrease in water content of the skin which leads to dry rough skin, flaking and irritation.

What is transepidermal water loss (TEWL)?

Transepidermal water loss refers to the water that is able to pass through the epidermal layer, the outermost layer of the skin, and evaporate in the air. This is a normal and natural process: the water is distributed from the blood circulation to the tissues, including the deep dermal layers, and from here up to the most superficial layers of the skin where eventually it evaporates into the air. TEWL does not refer to the water loss through sweat glands.

How is transepidermal water loss regulated?

The epidermal layer is made of keratinocytes, the skin cells, which are like bricks on top of each other’s and in between them there is a lipid matrix made of cholesterol, ceramides and other fatty acids that seal the gaps between the cells. There has to be an equilibrium in the synthesis of these components in order to keep TEWL to a certain physiological level. Higher transepidermal water loss is generally associated with skin barrier impairment.

How to prevent excessive TEWL and repair the skin barrier?

Several factors can damage the epidermal layer of the skin:

  • Cold, wind and low humidity. Weather can damage the skin and decrease its water content. Protecting it against harsh weather conditions can prevent skin barrier impairment and increased TEWL.
  • UV light. UV rays cause harm to the skin in many ways; by damaging it, they also increase TEWL. Always wearing a sunscreen can prevent this from happening as well.
  • Irritating chemicals. Toluene, chloroform and many other chemicals damage the skin. Always use personal protective equipment (PPE) and the right precautions when handling them.
  • Harsh skin cleansers. Cleansers help us get rid of dirt, dead cells and excess oils and sebum. Harsh cleansers may also strip the skin from essential lipids disrupting the fat matrix between skin cells; moreover, some cleansers can also denaturate skin proteins. Limiting the amount of time the cleanser stays on the skin, or limiting the number of applications, or using milder cleansers suited for your skin type can prevent damage from happening due to their use.
  • Excessive scrubbing. Excessive exfoliation of the skin is another way of disrupting our natural barrier.

A very simple way to protect the skin and help repair the skin barrier overall reducing water loss is to use a moisturizer. Not all moisturizers are the same and not all skin types need the same moisturizers. There are humectants, occlusives and emollients and each one works in a different way. Find out the difference between them in the dedicated article to understand which one may be more appropriate for your specific case.



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