Transepidermal Water Loss (TEWL): The Reason Your Skin Is Always Dry
Transepidermal Water Loss (TEWL): The Reason Your Skin Is Always Dry
Skin is constantly losing water — even when you do not sweat. The process is called transepidermal water loss (TEWL), and it is why your skin can feel dry even after drinking 3 litres of water.
What TEWL Is
Water evaporates from the deeper skin layers through the surface into the air. A healthy barrier slows this; a damaged barrier accelerates it.
On a healthy adult, TEWL is around 5–10 g/m²/hour. After hot showers, harsh soaps, or in dry climate, it can spike 2–3x.
Why Drinking Water Alone Will Not Fix It
Internal hydration helps but cannot stop water from leaving through a damaged barrier. The barrier needs topical support too.
What Slows TEWL
Occlusives (shea butter, cocoa butter, mineral oil) form a film that physically blocks evaporation.
Humectants (glycerin, hyaluronic acid) draw water from deeper layers and the air into the surface.
Emollients (squalane, fatty acids) fill gaps in the barrier and improve its integrity.
The Best TEWL-Fighting Routine
Lukewarm shower → pat dry → humectant + emollient lotion within 60 seconds → in winter, add an occlusive on shins, elbows, hands at night.
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