TEWL. Trans-Epidermal Water Loss is the technical term for the amount of water that leaves your body through your skin (your epidermis) by diffusion and evaporation.
This water loss happens all the time, but the amount lost changes depending on atmospheric conditions and how damaged or hydrated your skin is. Here in California, where the climate is almost always dry, it is something you need to be especially aware of, because dry and windy climates increase TEWL. TEWL also increases when there is not enough water in our skin or when there is damage (burns, wounds, sunburns, etc.) to our skin.
What can we do to try to reduce this water loss? We can stay away from things that damage our skin, like excessive sun or wind and temperature extremes. We can use humidifiers in our homes, if we live in a place where the humidity is below the ideal of 40-60% ideal.
But perhaps the easiest thing to do is to apply things to our skin that will keep the water in. Thick moisturizing creams, like Supple, create a barrier that makes it difficult for water to leave the epidermis, reducing TEWL. However, that film on the skin disappears after a few hours, so it is important to re-apply. If you don’t want to use a cream, you can use anything with high levels of linoleic acid. Linoleic acid cannot be made naturally by human bodies, but is an important component of ceramides, one of the skin’s main moisturizing elements. Gamma-linoleic acid (GLA), in particular, has been shown to be one of the most effective agents for maintaining skin’s water content, and it can be found in oils like borage oil. Other linoleic acids can be found in evening primrose and pumpkin seed oils. Any of these, applied to your skin, will help protect from TEWL.