What’s transepidermal water loss (TEWL)?Updated a year ago
Transepidermal water loss is technically a measurement of how much water is lost from the epidermis.
Watch out, we’re about to get science-y! Feel free to scroll on down if you just want to learn how to address TEWL effectively, and don’t really care about how it happens.
So basically, water loss happens through the outermost, protective layer of skin called the stratum corneum, which is composed of flattened, de-nucleated dead skin cells called corneocytes. Between those dead skin cells, we have an intercellular matrix composed of lipids that maintain the moisture-trapping abilities of the stratum corneum to keep the entire epidermis (i.e. the main layer of the skin, which includes the stratum corneum and 4 more sub-layers below it) hydrated.
Humans are always experiencing TEWL, but it’s a question of to what extent. Low water loss is good because it means your skin actively retains moisture. It corresponds with healthy, hydrated skin that feels plump, springy, resilient, and not inflamed.
High TEWL is bad - it leads to dry, irritated brittle-feeling skin, and it’s a sign that something is wrong with your skin barrier. Skin experiencing a lot of water loss will be more susceptible to external damage, resulting in further dryness, redness, and irritation. It may even lead to clogged pores since barrier issues can impede the skin cells’ natural ability to shed.
In the long term, constant dehydration will get in the way of the skin’s natural shedding and renewing mechanisms, leading to textural issues, higher susceptibility to hyperpigmentation, and speeding up the visible aging process of the skin.
That’s why the main purpose of any good moisturizer should be to reduce and prevent TEWL. Scientists can actually measure TEWL, which is helpful when judging skin health or the efficacy of a skincare product.