Le Formulaire || What is TEWL?

You might have heard the use of the acronym TEWL before, we may have even casually used it here at Le Formulaire. But do you know what it means? Trans Epidermal Water Loss (TEWL) is the measurement of water lost through the stratum corneum, or uppermost layer, of the skin. It accounts for approximately 350ml of the insensible losses we experience daily. Some internal factors influence TEWL, such as the size of the skin’s corneocytes that compose the stratum corneum – the smaller the corneocytes, the more TEWL, hence why we experience more TEWL on the face. External factors like climate, season, pollution, skin disorders and even altitude can also affect TEWL.(1)

Trans Epidermal Water Loss (TEWL) is often used as a measurement of skin barrier function, as a well-functioning barrier should reduce TEWL. TEWL is influenced by the amount of water vapour pressure on either side of the skin, and so areas of high humidity are believed to cause less TEWL, helping to maintain a supple skin barrier.  Where there is abnormally high levels of TEWL you can experience dryness, irritation and flaking skin.(2)

How can we reduce TEWL?

 Moisturise

In order to reduce TEWL, we can use moisturisers to trap water and reduce its ability to evaporate into the environment. There are three types of moisturisers available, these being emollients, which are oil and lipid based. Emollients include ingredients such as ceramides and cocoa butter. The second type are humectants, which are based on ingredients such as hyaluronic acid and glycerine. Finally, the moisturiser best suited to prevent TEWL are occlusive moisturisers. These are oil based and include ingredients such as beeswax, petrolatum, and silicone. Emollients work by creating a protective seal over the skin to prevent water loss. The right mosituriser comes down to your skin type and only those with the driest skin tend to need occlusives to reduce TEWL.

Environment

Seasonal changes, sun exposure, and pollution can affect the rate of TEWL in our skin. The jury appears to be out when it comes to which season causes more TEWL than another, with some studies finding that summer causes more TEWL and others claiming that winter is the biggest offender. We recommend that you keep an eye out to see the changes in your own skin throughout the seasons to see what time of year your skin feels dryer. If you live in a dry climate with little humidity, you may want to invest in a humidifier for your home to increase your skin barrier’s ability to retain water. 

Sun exposure has also been linked to more trans epidermal water loss, as the oxidative damage to the skin also affects the cells of the epidermus and the skin’s ability to maintain moisture.(3) Yet another reason to apply your sunscreen and stay in the shade!

Pollution is found to have an effect on our skin’s ability to maintain its moisture levels, with studies finding that those who live in urban areas experience more TEWL than those who live in rural locations. Make sure to use an anti-oxidant in your morning skincare routine to combat the effect of free radical damage due to particulate matter pollution in our air.

TEWL is a natural process that occurs in our skin that can lead to dryness when it is poorly controlled, and this can lead to irritation and make our skin appear more aged and dull. To combat these factors, consider using a moisturiser that suits your skin type, wear sunscreen daily, and include antioxidant protection in your regime. Additionally, at Le Formulaire we recommend looking at how you can adapt your environment to improve water retention in your skin and enhance that dewy complexion!

(1)   Green M, Kashetsky N, Feschuk A, Maibach HI. Transepidermal water loss (TEWL): Environment and pollution-A systematic review. Skin Health Dis. 2022 Feb 25;2(2):e104. doi: 10.1002/ski2.104. PMID: 35677917; PMCID: PMC9168018.

(2)   Honari, G., Maibach, H. Skin Structure and Function. Applied Dermatology, 2014

(3)   Prihadi, I. A., Ellistasari, E. Y., and Kusumawardani, A. (2022) "The Difference In Transepidermal Water Loss (TEWL) Values Between Sun-exposed and Non-sun-exposed Skin Among Male Medical Students," Journal of General - Procedural Dermatology & Venereology Indonesia: Vol. 6: Iss. 2, Article 4. DOI: 10.7454/jdvi.v6i2.1003