TEWL, which stands for Trans-Epidermal (aka skin) Water Loss, is exactly what it sounds like - water loss through the skin.
The skin is comprised of three primary layers: the epidermis, the outermost layer; the dermis or middle layer; and the hypodermis, the undermost layer. When water passes from the dermis through the epidermis and evaporates from the skin’s surface, this is known as trans-epidermal water loss, or TEWL.
While water loss is a normal process (sweating) that your skin naturally balances, skin with eczema seems to have a tougher time balancing it correctly.
Eczema is notoriously difficulty to measure, and doctors have been trying for a long time to come up with a consistent way to compare eczema across people. TEWL is interesting because it can be measured simply by putting a probe gently on the skin.
An example of a TEWL-meter
A study of almost 2000 newborns at Cork University Maternity Hospital took TEWL measurements of babies when they were 2 days old, 2 months, and 6 months. The babies were followed until they were 12 months old, and the TEWL measurements were compared to later diagnosis of eczema. A high TEWL score means the baby's skin was losing a lot of water, while a low score meant the skin was properly trapping the right amount of water.
The doctors found that a high TEWL score at 2 days old could predict eczema at 12 months, and a low TEWL score predicted an eczema free baby at 12 months.
And babies who develop eczema early, and babies with more severe eczema, are more likely to develop food allergies. The basic idea or conclusion is that very early on, using totally harmless methods, you may be able to assess a babies risk for developing eczema, to asthma, to food allergies and so on.This finding could be huge for parents who have a family history of eczema or allergies, to know that they should begin using emollients right from birth and introduce allergens early.