Q: What is Transepidermal Water Loss?


Transepidermal Water Loss, or TEWL for short, is probably one of those skincare phrases that you’ve seen used to promote hydrating and protecting products, but may not have a complete grasp on. Or, you may have never come across this phrase at all, and it’s left you feeling a little stumped. Not for much longer…


In short, TEWL refers to the natural process of water vapour evaporating through your skin and into the atmosphere. Trans meaning across, and epidermal referring to your epidermis (the top layer of your skin). Whilst we talk about reducing TEWL with skincare, it’s part of our healthy bodily functions and we wouldn’t want to stop it completely! In fact, we tend to lose 300-400ml of water per day through this process. This may seem like a lot of water, but evaporation means it quickly disappears.

The reason that TEWL has become an important buzz phrase has a lot to do with how we identify increased water loss as a signal that your skin barrier health needs some help! So let me go on a detour for a second…

An easy way to picture your skin barrier is by imagining your skin cells as bricks, held together by ‘cementing’ lipids (fats and oils). Additional skin damage or stress can weaken how well the lipids work as cement, allowing gaps to form. This is bad news not only because more moisture is able to escape, but there’s opportunity for bacteria, irritants, or allergens to get in. This is how we can end up with dry skin conditions, bad breakouts, and very sensitive feeling skin. There are a couple of factors that can weaken your skin barrier, such as using super hot water in the shower or vigorously washing your face which can strip the lipids away. Ingredients that can lead to irritation (like SLS) and strong fragrances can also lead to lipid damage.


But back to TEWL! There are some environmental factors that can affect how much moisture is being lost, such as humidity. More humidity = less TEWL, which is why we often face more dryness and sensitivity in winter rather than summer. But generally, if your epidermis is lacking enough lipids to keep defences strong, we’re going to see an increase in Transepidermal Water Loss.

So, how do we keep TEWL to a healthy rate? Moisturise! Okay, it’s a little more complex… If you remember from our blog on Hyaluronic Acid, there are three types of moisturisers that we need to use in balance to see the best results.


Humectants are the first, which are ingredients that draw moisture back from the atmosphere into our skin, focusing on replenishment. Our favourite example is Hyaluronic Acid, or Glycerin! Look for our Hyaluronic Acid Facial Serum, Hyaluronic Acid Hydrating Cleanser or Hyaluronic Acid Face Mist, which can easily be slotted into your regime. Don’t forget, Hyaluronic Acid works best when applied to damp skin. Our Q+A Peptide Facial Serum or Zinc PCA Daily Moisturiser will also provide you with a moisture boost too!

The second type is occlusives, which are barrier creating ingredients that offer your skin physical support, giving time to your natural barrier to rejuvenate and rest. Beeswax, like in our Collagen Face Cream, is a great example of an occlusive ingredient. These are generally not the most non-comedogenic ingredients, so oily and acne-prone skin types should keep this in mind, perhaps opting for humectants and emollients instead!

The third, and most versatile, are emollients, which combine the benefits of both humectants and occlusives, providing both moisture to be absorbed, and a physical barrier to protect against moisture loss. A great emollient is another of our favourites, Squalane! Plus, it’s non-comedogenic so perfect for our oilier skinned friends. You can also look for Shea Butter and Cocoa Butter. Check out our Grapefruit Cleansing Balm, Vitamin A.C.E. Warming Gel Mask, Chamomile Night Cream and Squalane Facial Oil for an emollient-packed line-up!


Now we have the lowdown on TEWL! Hydrated and protected skin awaits.

Amy @ Team Q+A



Amy Robson


Aspiring author, craft addict, and Q+A's eCommerce Coordinator

Leave a comment