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What’s All This Talk About TEWL?

What’s All This Talk About TEWL?

What is trans-epidermal water loss & what does it mean for my skin?

Hello, lovely readers! As you know, Codex Beauty Labs relishes in delivering insider knowledge on all-things-skin, so this week we’re addressing the buzzed-about beauty acronym on everyone’s lips— TEWL. Read on to learn what it is, how it impacts your skin, and how we measure it and treat it using innovative formulations.


What Is TEWL & Why Is It Important?

TEWL is known as Trans-epidermal water loss -  the amount of water vapor that naturally escapes through the skin barrier or skin surface. Water vapor loss is a good indicator of the integrity of the skin barrier function which inherently refers to the skin's ability to retain moisture. Water retention is one key function of the skin barrier, so an increase in TEWL indicates a significant alteration of the skin barrier function leading to de-hydration and inflammation; for example, burns, psoriasis, and both atopic and contact dermatitis are diagnosed by an increased TEWL.  Chemical or mechanical damage to the skin barrier may also increase the TEWL, such as from skin irritation from detergents, organic solvent, skin stripping or extensive occlusion.

Your skin barrier protects your complexion from harm, including maintaining the appropriate amount of balanced hydration. An increase in the TEWL indicates an impaired barrier function which often correlates to skin aging or afflictions such as psoriasis, disorders of keratinization, and atopic dermatitis.


How Do We Measure TEWL?

Fun Beauty Fact: Interest in measuring/quantifying moisture loss from the skin has existed for over a century, with the first recorded attempt to measure water loss occurring in 1614.

At Codex Beauty Labs we measure TEWL to determine the effect of our products on skin barrier (aka the stratum corneum) health. By quantifying the amount of water vapor escaping through the stratum corneum, we can estimate skin barrier “lossiness” or “integrity,” and correlate the rate of loss to the severity of potential skin dehydration.  TEWL is a sensitive indicator of skin irritation and is widely used in objective analysis of irritancy potential or protective properties of topical skincare products. 


Our efficacy tests use a TEWL analyzer such as an AquaFluxTM or C+K Tewameter TM300/HEXTM to assess skin surface water loss at the same site on face or body on day 0 of the study (baseline) and after using our products for a specific time period (e.g., 14, 28, 56 or 84 days).

It is important to note that the average TEWL in humans is about 300–400 mL/day; however, it can be affected by environmental and intrinsic factors. For example, in high humidity, the amount of water loss decreases, whereas in dryer climates, the amount of water loss increases.  TEWL varies in different anatomic sites and is inversely related to the corneocyte size, so we actually lose the most water through our hands and feet.  It also varies by race and age, and many more studies need to be done to understand the impact of diversity on TEWL.


How Does A TEWL Meter Work?

Diffusion is the movement of a substance from an area of high concentration to an area of low concentration. TEWL analyzers today use the concept that water vapor will diffuse across a membrane (e.g. your skin) owing to a concentration gradient. So they infer this concentration gradient by measuring the relative humidity and temperature at two points separated by a fixed distance, and extrapolate the rate of water vapor loss (TEWL) at the skin’s surface.  For the detail-oriented readers among you, the relative humidity actually has a precise technical definition which means “the partial pressure of water vapor divided by the saturated or equilibrium water vapor pressure at that temperature”. The partial pressure is, of course, the fraction of the pressure that is contributed by water vapor. This is why the relative humidity and temperature must be measured in the TEWL meter. 


A TEWL analyzer features either:

  • two temperature/relative humidity sensors inside an open cylindrical chamber where the water vapor flows freely, or
  • one temperature/relative humidity sensor inside a closed cylindrical chamber with or without a cooling plate at one end that freezes the water vapor and essential brings the humidity to zero, a known reference point (NOTE: Without a cooling plate, the gradient is rapidly affected by the accumulation of water vapor at the top of the closed chamber leading to inaccuracy.).


Hand-held versions are becoming more prevalent as they can be used to measure water loss at any time. Worried about a compromised skin barrier? Is your skin subject to a harsh environment? Worried about too much retinol and peelings?  Worried about those dry patches on your knees?   Want to see how well a skincare product is protecting you from dehydration?  For all of the above, check your TEWL.

Pretty exciting stuff, huh?! We love the continuous advancements science is making in the world of beauty.


Why Do We Measure TEWL?

Increased trans-epidermal water loss can lead to premature aging including fine lines, wrinkles, and thinning of the skin. To counteract and treat TEWL we focus on delivering hydration to increase water continent deep within the skin and moisturizing to protect the skin barrier and keep your skin looking supple and radiant.


What Can You Do About TEWL?

Unsure where to begin protecting against TEWL? Add one or several of our best-selling skin savors to your rotation to target TEWL in different ways!

Both of our Antü and Bia collections address TEWL with data-backed results straight from the lab. For example, our NEW fast-acting  Antü Brightening Serum protects, adds moisture, and decreases TEWL with amazing clinical results. In fact, 97% of our test subjects experienced a whopping 44% decrease in TEWL at 8 weeks.


Beauty Scoop:

Did you know The Antü line is a Byrdie favorite? Discover how our Antü collection uses hyaluronic acid and proprietary blends from Patagonia to boost hydration from the inside out and ingredients backed by efficacy data to address TEWL.



Our award-winning Bia Skin Superfood is a rich restorative cream that addresses skin hydration and moisture retention with 77% of test subjects experiencing a 13% decrease in TEWL at 4 weeks. Made with our revolutionary BiaComplex™, it is clinically proven address dry, flaky and itchy skin. Did You Know: We lose the most water through our hands and feet so Bia Skin Superfood is amazing at addressing TEWL as it expertly hydrates not only on the face, but also your entire body.



Antü Brightening Moisturizer protects and aids in UV recovery while also refining your pores. 74% of test subjects experienced a 19% decrease in TEWL at 4 weeks as our AntuComplex™ formula works hard to seriously re-hydrate your skin and remove dullness.





Bia Wash Off Cleansing Oil targets impurities without stripping—with 88% of test subjects experiencing 8.0% decrease in TEWL at 4 weeks.




We hope you find these targeted treatments useful. As always, reach out to us directly if you need assistance in creating a custom protocol to address TEWL. We’re always happy to help.


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