What Is Transepidermal Water Loss (TEWL) + How to Stop It

You know that feeling when you wake up and your skin feels extra dry? That’s (no) thanks to transepidermal water loss, or TEWL. TEWL is the process by which coveted, needed water escapes our skin into the air. While it’s super normal and is happening to literally everyone all the time, it’s also a bummer for your skin. Losing moisture can mean your skin looks dull and is more susceptible to wrinkles and even acne caused by irritation. But why would we let an invisible, common process mess so hard with our skin goals? Thankfully, and with the help of Laura Cline, Youth To The People’s Director of Education, we have everything you need to know about TEWL—how to minimize the damage.

360 HYDRATION

Like almost all our body’s functions, TEWL is tied intimately to our circadian rhythm. This means that although we experience TEWL at all times, we tend to focus on what happens with water loss overnight, when our bodies are in repair mode.

“Typically we speak about TEWL at nighttime because our body temperature lowers, skin temperature rises and the skin can become more acidic, so you do a lot of cell work. Because of this, you just tend to lose a lot more water from the skin barrier while you’re sleeping,” says Cline. “If you sleep in a place with low humidity, that’s dry, or high elevation, your skin will tend to feel dehydrated. Also, having a heater on during winter means that the air itself is dehydrated, which means that your skin would be even more dehydrated.” 

Essentially, the air is like a sponge, and if it’s dry it will suck the moisture out of your skin at a faster rate. The solution? Create your own moisture! Cline suggests investing in a humidifier, which can regulate the moisture in the air.

To decrease TEWL, you also need to be moisturizing from within. If the layers of your dermis are properly hydrated, TEWL will have a harder time depleting you. Unfortunately, just drinking a bunch of water before you go to bed is only going to wake you up for the bathroom. Hydrating your internal atmosphere is an all-day commitment. Keep a reusable water bottle around at all times!

Read more about why topical hydration is essential. 

SKIN BARRIER STRENGTH

In addition to body temps that trigger moisture evaporation, your skin barrier, which keeps moisture in and free radicals out, is also weakened during night time. This is significant to cosmetic chemists; the products you apply at night can be better absorbed into your skin. Unfortunately, a weak skin barrier also means higher rates of TEWL. Over-stripping your skin with harsh cleansers can further weaken your skin’s natural ability to retain moisture throughout the night. To protect your skin barrier, Laura Cline suggests the sulfate-free, super gentle Superfood Cleanser.

“Your skin barrier is a whole ecosystem. It’s about having a healthy microbiome and pH level. Balancing that means you’re not totally disrupting your moisture barrier,” says Cline.

MOISTURIZING 101

Now that your body and air are properly hydrated and humidified, it’s time to get into the science of moisture. Proper moisturization comes down to three key terms: humectants, occlusives, and emollients.

Humectants are moisturizers that hydrate based on their “hygroscopicity.” This means that humectants attract and bond water—but in an unstable way that can easily be reversed, i.e. evaporated. Humectants draw water deep from the dermis, and from around you in a humid environment (another reason why 360 hydration is so essential to healthy skin.) “Humectants like glycerin, hyaluronic acid, and betaine are all things we have in our formulas,” says Cline. The Superfood Air-Whip Moisture Cream is a humectant favorite.

With humectant moisture on lock, now it’s time to lock it in. Occlusive agents act as a hydrophobic barrier over the skin to lock in the moisture provided by humectants. Emollients are a type of occlusive agent, with the bonus of giving your skin a smooth effect.

“Emollients are something in a cosmetic formula, like an oil or conditioning agents that would keep humectants locked in your skin,” explains Cline. “In YTTP products, we use things like jojoba oil, shea butter, and squalane. These are non-comedogenic and lock in moisture. Thankfully, the Adaptogen Deep Moisture Cream has all three.

Because stopping TEWL is all about locking in moisture, and the emollient squalane packs a punch. Using an overnight treatment like the Superberry Hydrate + Glow Dream Mask, means you’re prolonging the “locking in” protection of your emollients.

When you use both humectants and emollients/occlusive agents, you’re making sure you get that hydration to your skin—and that you’re keeping it.

SPF and a great moisturizer are two solid keys to maintaining skin health—and though we willingly slather on SPF to protect our skin from the sun’s rays, it’s important to remember to protect ourselves against TEWL once the sun goes down. TEWL won’t leave you with a big red sunburn, but the long term effects are worth protecting against. Remember: to stop TEWL, keep yourself hydrated, invest in a humidifier, apply both humectants and emollients, and treat your skin barrier right.

Written by Lee Phillips for Youth To The People