The natural skin hydration process and transepidermal water loss (TEWL)
Defined as a measurement of the quantity of water that passes from inside a body through the epidermal layer to the surrounding atmosphere via diffusion and evaporation processes. This is a continuous process over which we have little control. It can increase due to disruption to the skin barrier (wounds, scratches, burns, exposure to solvents or surfactants, extreme dryness) and is affected by humidity, temperature, season, and moisture content of the skin (hydration level).
So what can we do to reduce TEWL? We can stay away from things that damage our skin, like too much sun or wind exposure, extremes in temperatures, or really scratchy sweaters. We can live in a humid climate or have a humidifier in the house (40% to 60% humidity is ideal). And we can make lovely creations that will trap water into our skin or add more when needed.
Again, using a mild cleanser with re-fatteners in it will help a lot, as well as using lotions and creams. Thick moisturizing creams (those with nice butters or other occlusive ingredients) will reduce TEWL due to the occlusion. As the film on our skin disappears (it takes a few hours), the TEWL will increase, so re-applying our lotions is a good thing.
Light, moisturizing lotions (those with high water contents) will actually increase TEWL as measured by that the ServoMed Evaporimeter, but there’s a reason for this – the evaporation of the water from the lotion itself increases the measurement and the evaporation of water from our skin…because we now have enough water in our skin, so the rest evaporates! You can make a light, moisturizing lotion more occlusive by using things like allantoin or dimethicone – these will form a barrier that will stop the evaporation, if you don’t want to use butters! And aloe vera or other polysaccharides like hydrolyzed protein will offer a light moisturizing gel layer that can reduce water loss slightly.