TEWL stands for trans epidermal water loss. It is the “unperceived” loss of water through our skin, in distinction to the “perceived” loss of water when we sweat. It is also sometimes called insensible water loss. It has been known for quite some time that children and adults with eczema have a greater TEWL than normal, but the difference has never been carefully measured. The Allergy and Asthma Proceedings recently published new research doing just that.
The measurements were adjusted for body surface area and were 2 ½ times greater in people with eczema than those without. This water loss leads to excess dryness of the skin which disrupts the barrier function of the skin. Think of the cracks in the bottom of a dry lake bed. These micro-cracks in the skin allow ingress of both allergens (such as pollen, dust mites, animal dander) and irritants (such as soap, preservatives in personal care products including their fumes) to get “under the skin” and therefore potentiate the eczema. Two simple strategies work: maintain good hydration and always apply a moisturizer after bathing.