Transepidermal Water Loss (TEWL)

Invisible Water Loss

Your skin is not a waterproof barrier. Water constantly migrates from the deeper, well-hydrated layers of the dermis through the epidermis and evaporates from the skin's surface into the surrounding air. This process, transepidermal water loss, happens 24 hours a day, even when you are sleeping. In healthy skin with an intact lipid barrier, TEWL occurs at a controlled rate of roughly 300 to 400 mL per day across the entire body surface.

When the skin barrier is compromised (by harsh cleansers, dry air, sun damage, or skin conditions like eczema), TEWL accelerates dramatically. The skin loses moisture faster than the body can replace it from within, creating the dry, tight, flaky, uncomfortable skin that sends people searching for a better moisturizer.

What Increases TEWL

Low humidity environments (air-conditioned rooms, heated indoor air, airplane cabins) increase TEWL by creating a steeper humidity gradient between the skin surface and the surrounding air. Hot water washing strips natural lipids faster than lukewarm water. Alkaline soaps disrupt the acid mantle. Over-exfoliation thins the protective outer layer. Wind exposure accelerates surface evaporation. Each of these factors removes or disrupts the components of the skin barrier that normally slow water loss.

The Three-Part Defense

Effective moisturization addresses TEWL through a combination of three ingredient types. Humectants (like glycerin and honey) attract water molecules from the air and deeper skin layers. Emollients (like shea butter and coconut oil) fill gaps between skin cells and restore the lipid matrix. Occlusives (like beeswax and petrolatum) form a physical barrier on the skin surface that prevents evaporation. Our lotion bars and body butters combine all three mechanisms: beeswax as the occlusive, shea butter and coconut oil as emollients, and the natural humectant properties of honey compounds retained in the beeswax.