“Trans-epidermal water loss (or TEWL) is 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.” (Wikipedia) This is a continuous process over which we have little control. It can increase due to disruption to the skin...

If you’ve just joined us, please check out this post on the chemistry of your skin before reading onwards… If we think of the corneocytes in the stratum corneum as “bricks”, then the stratum corneum lipids are the mortar. (The water soluble natural moisturizing factor is found inside the corneocytes; the lipid soluble stratum corneum...

Natural moisturizing factor (NMF) is found within the corneocytes, and makes up 20% to 30% of the dry weight of the stratum corneum. It consists of amino acids (40%), sodium PCA (12%), lactate (12%), urea (7%), ions (18.5%), sugars (like glycerol – 8.5%), and a few other things. These are water soluble humectants (meaning they...