Transepidermal Water Loss: Causes, Treatment & Tips to Prevent It

Your skin does a lot for you every day, from shielding against environmental stressors to keeping precious moisture locked in. However, some of that moisture naturally evaporates from your skin into the air, a process known as transepidermal water loss (or TEWL). While TEWL is inevitable and a totally normal biological process, increased TEWL can be caused when your skin’s balance gets disrupted and it starts losing water faster than it should — and it’s a common culprit behind dryness and irritation.

The good news? Understanding what causes TEWL is the first step toward keeping your skin barrier strong and comfortably hydrated. Below, we’ll break down what TEWL really means, what can trigger increased TEWL, and how a good SPF moisturizer can help your skin stay soft, smooth, and protected.

What Is Transepidermal Water Loss?

Transepidermal water loss (TEWL) refers to the amount of water that naturally evaporates from your skin into the air. It’s part of a normal biological process. Your skin is constantly balancing internal hydration with the external environment. But when that balance is thrown off, TEWL increases, and your skin can start feeling tight, dry, or sensitive.

Your skin barrier—made up of the stratum corneum and the acid mantle—carefully regulates this process:

Stratum corneum: The outermost layer of the epidermis, made up of flattened cells called corneocytes. Think of it as the brick wall that keeps your skin resilient.
Acid mantle: A thin, protective layer on top of that wall, made from ceramides, cholesterol, fatty acids, and sebum. This helps seal in moisture and protect against external stressors.

When either part of this barrier is compromised, water can escape more easily. That moisture loss not only leaves skin feeling dehydrated but can also make it more prone to redness, flaking, and even increased sensitivity to the sun and pollution.

What Causes Transepidermal Water Loss?

Some level of water loss is totally natural. But certain factors can speed it up and make skin feel more parched than protected.

1. Low Humidity and Dry Air

If you’ve ever noticed your skin feeling tight after a long flight or a night with the heater running, that could be TEWL at work. Dry air pulls moisture from the skin’s surface, increasing water loss. Environments with air conditioning or central heating can have the same dehydrating effect, especially overnight.

2. UV Exposure

UV rays don’t just cause sun damage—they also weaken the skin’s moisture barrier. Over time, this can make it harder for your skin to retain hydration, leaving it feeling dry and compromised. Daily SPF is key to helping minimize this effect.

3. Sleep and Circadian Rhythm

Believe it or not, your skin loses a lot of water while you sleep. As your body’s temperature drops and skin temperature rises, your pH becomes slightly more acidic, all of which encourages moisture evaporation.

4. Aging

As we age, the skin’s natural ability to repair itself slows down. The epidermal layer becomes thinner, and sebum (your skin’s natural oil) production decreases. Together, that means less protection and more water loss.

2 SPF Moisturizers to Help Keep Your Skin Hydrated and Protected

Using an SPF-infused moisturizer is one of the easiest ways to care for your skin. Here are two Supergoop! favorites that hydrate, support, and protect all at once.

Superscreen Hydrating Daily Cream SPF 40

We believe sunscreen should be an easy, essential part of your daily routine, so we added it to your morning moisturizer. Superscreen is a soft, rich cream with a natural finish that delivers deep hydration and daily protection. Its fast-absorbing formula features ectoin and ceramides to help replenish and fortify your moisture barrier while providing broad spectrum SPF 40 protection. It’s suited for normal, combination, or dry skin types that crave comfort and lasting hydration. By combining intense hydration with SPF protection, Superscreen helps prevent the dehydration that can result from UV exposure, leaving skin feeling smooth and comfortably moisturized.

Triple Prep Weightless Multitasking Moisturizer SPF 40
Triple Prep was made to be your essential morning moisturizer: It hydrates, supports, and protects your skin in one powerful step. As well as broad spectrum SPF 40, this multitasking formula features a hydrating complex of ectoin, hyaluronic acid, and glycerin, which helps support and replenish skin’s moisture barrier while protecting against oxidative stress caused by blue light, radiation, and pollution. The result is skin that feels replenished with hydration, comfortably balanced, and prepped for the day!

Keep Moisture In, Keep Skin Happy

Water loss is a natural part of how your skin functions, but that doesn’t mean you have to put up with dryness or irritation. With the right routine, you can support your skin’s barrier, lock in lasting hydration, and protect it from the everyday factors that can throw it off balance.