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Water loss through the skin, called transepidermal water loss or TEWL, is measured with a probe that reads the water vapor rising off the skin in grams per square meter per hour, and you slow it by doing two things at once: putting water-binding humectants on damp skin and sealing them with barrier lipids or an occlusive layer. Hydration alone does not stop evaporation. In human studies, petrolatum sped up barrier recovery after the barrier was disrupted, and a cholesterol-dominant lipid mix sped up recovery in aged skin.
I am a cosmetic formulator, and TEWL is one of the numbers supplier labs report when they test a moisturizer or an active. This guide explains how TEWL is measured, how to read your own skin at home, which ingredients slow water loss, and the exact routine I use when skin feels tight no matter how much serum goes on. For the basic definition and science of TEWL, see our companion article, What Is Transepidermal Water Loss.
How TEWL is measured
TEWL is a passive, invisible flow of water vapor from the deeper skin layers out through the stratum corneum. Instruments measure it by sitting a probe on the skin and reading the humidity gradient just above the surface. The EEMCO guidance for cosmetic science (Rogiers, 2001) describes the main use of these readings: supporting claims about mildness, hydration and barrier effects, and screening ingredients for how they affect barrier function.
| Method | How it works | Where you see it |
|---|---|---|
| Open chamber | Two sensors in an open cylinder measure the vapor gradient above the skin | Classic research and cosmetic testing labs |
| Closed chamber | A small closed cap collects vapor and reads the rise in humidity | Handheld devices used in supplier claim tests, such as the VapoMeter |
| Condenser chamber | A cooled surface condenses vapor, keeping the chamber humidity steady | Longer or continuous measurements |
Readings shift with room temperature, humidity, body site, recent washing and product left on the skin, which is why labs acclimatize volunteers before measuring and why a single home reading means little. A 2018 meta-analysis of healthy adults (Akdeniz and colleagues) pooled TEWL values from 212 studies covering 86 skin areas and found TEWL is highly dependent on body site, with a symmetrical pattern between left and right. A 2022 systematic review (Green and colleagues) concluded that defining a single "normal" TEWL value is currently problematic because age, BMI, bathing habits and other factors move the number.
What that means for you: compare your skin to itself, on the same site, under the same conditions, over time. That is exactly how ingredient suppliers report TEWL: as a percentage change from day 0.
What a TEWL result looks like in a supplier test
Here is a real example from one of my supplier files. A lotion containing 5% of a copper tripeptide solution (SpecKare E-GCu11) was tested on the faces of 20 women aged 20 to 55, with TEWL measured by a VapoMeter (supplier data):
| Day | TEWL change vs day 0 |
|---|---|
| 14 | -17.82% |
| 28 | -27.91% |
| 56 | -31.37% |
A falling TEWL number means less water escaping. Notice the time frame: the change kept building over 8 weeks. That is typical. Barrier-supporting routines are judged in weeks, not hours.
How to read your own skin at home
You cannot calculate TEWL with a mirror, but you can track the signs consistently:
- Cleanse with lukewarm water and a gentle, fragrance-free cleanser. Pat dry.
- Apply nothing and set a timer for 20 minutes.
- Score tightness, flaking, dullness and stinging from 0 to 3 in a notebook.
- Note the indoor conditions: heating, air conditioning or a humidifier.
- Repeat at the same time of day three times a week for four weeks while you change your routine.
A consumer moisture meter can add a number to your notes, but it reads surface hydration, not TEWL. Use it the same way: same spot, same time, compared to yourself. If dryness comes with cracking, bleeding, swelling or persistent burning, see a dermatologist rather than adjusting products.
The three ingredient jobs that slow water loss
| Job | What it does | Examples | Use it |
|---|---|---|---|
| Humectant | Binds water in the outer skin | Glycerin, sodium hyaluronate, panthenol, aloe | On damp skin, first |
| Barrier lipids and emollients | Fill gaps between surface cells and soften texture | Ceramides, cholesterol, fatty acids, squalane, plant oils | In the moisturizer |
| Occlusive | Forms a film that physically slows evaporation | Petrolatum, waxes, shea butter, some silicones | Last, a thin layer, especially at night |
Humectants: glycerin is the workhorse
A review in the British Journal of Dermatology (Fluhr, Darlenski and Surber, 2008) describes glycerol as a contributor to stratum corneum hydration, elasticity and barrier function, with reported effects that include better hydration and protection against irritants. Glycerin and sodium hyaluronate both work best on damp skin, followed by a layer that keeps the water in.
Lipids: the ratio matters
Zettersten and colleagues (1997) tested topical stratum corneum lipids on aged skin. In aged mice, a cholesterol-dominant mixture of cholesterol, ceramides and free fatty acids in a 3:1:1:1 molar ratio sped up barrier recovery at 3 and 6 hours compared with an equal mix, while a fatty-acid-dominant mix delayed it. In six aged human volunteers, the cholesterol-dominant mixture significantly sped up barrier recovery at 6 hours. The takeaway for shopping: a moisturizer with a complete lipid set beats one that lists a single ceramide. Our guide to strengthening the skin barrier covers the daily habits side, and if you are choosing a lightweight emollient, see is squalane comedogenic.
Occlusives: they help, they do not suffocate
Ghadially, Halkier-Sorensen and Elias (1992) disrupted the skin barrier with acetone in human volunteers and applied petrolatum. Instead of slowing recovery, as expected from occlusion, petrolatum accelerated barrier recovery. A thin occlusive layer at night is one of the most effective steps you can add when skin feels tight.
The routine I use for skin that will not stay hydrated
Morning
- Rinse with lukewarm water, or a gentle cleanser if needed. Skip hot water.
- While the skin is still damp, apply a humectant serum: sodium hyaluronate gel (recipe below) or our Hyaluronic Acid Plumping Serum.
- Within 60 seconds, apply a moisturizer with barrier lipids or squalane.
- Finish with broad-spectrum sunscreen.
Evening
- Gentle cleanse. Double cleanse only if you wore water-resistant sunscreen or heavy makeup.
- Humectant on damp skin.
- Moisturizer, or a no-rinse overnight mask such as our HydroGlow Night Mask, which combines three types of hyaluronic acid with glycerin, jojoba and squalane.
- On dry nights, press a thin layer of an occlusive balm over the driest areas.
- Pause exfoliating acids, scrubs and retinoids until tightness settles, then bring them back one at a time.
DIY humectant gel at the highest recommended rate
This is the damp-skin layer in the routine above. Our sodium hyaluronate powder is a high molecular weight grade (800 to 1500 kDa) used at 0.1 to 2%, so this gel uses 2%.
| Ingredient | % | Grams (100 g batch) |
|---|---|---|
| Distilled water | to 100 | balance |
| Glycerin | 3 | 3.0 g |
| Sodium hyaluronate powder | 2 | 2.0 g |
| Leucidal Liquid | 4 | 4.0 g |
Method. Sanitize tools with 70% isopropyl alcohol. Mix the sodium hyaluronate into the glycerin to form a slurry, then stir it into the water slowly. Cover and let it hydrate for 4 to 12 hours until smooth and clear. Stir in the Leucidal at room temperature, fill an airless pump and label with the date. Use a pea-sized amount on damp skin, then seal with moisturizer within a minute.
Sensitive skin
Patch test each new product on the inner arm for 24 hours. For the gel above, start at the lowest rate on the product page, 0.1% sodium hyaluronate (0.1 g per 100 g), which makes a thin, watery serum, and work up toward 2% over several weeks. Introduce one new product at a time, and choose fragrance-free moisturizers while your skin is tight or stinging.
Water loss skin: frequently asked questions
What is a normal TEWL reading?
There is no single normal number. Large reviews show TEWL varies by body site, age, BMI, bathing habits and room conditions, so compare your skin with itself over time under the same conditions.
Can oily skin have high water loss?
Yes. Surface oil does not mean the barrier is holding water well. Tightness after cleansing, flaking around the nose and shine at the same time are common signs.
Why does hyaluronic acid sometimes make my skin feel drier?
A humectant applied to dry skin in dry air, with nothing over it, can leave skin feeling tight as the surface dries out. Apply it to damp skin and seal it with a moisturizer within a minute.
Is petrolatum bad for the skin barrier?
In a human study, petrolatum accelerated barrier recovery after the barrier was disrupted with acetone. A thin layer at night is a reliable way to slow water loss. If you prefer plant-based options, shea butter or a wax-based balm forms a similar film.
How long does it take to see a difference?
Skin can feel more comfortable within days. Measured TEWL changes in supplier tests built over 2 to 8 weeks, so track your notes for at least four weeks.
Sources
- Rogiers V. EEMCO guidance for the assessment of transepidermal water loss in cosmetic sciences. Skin Pharmacology and Applied Skin Physiology. 2001;14(2):117-128. doi:10.1159/000056341.
- Akdeniz M, et al. Transepidermal water loss in healthy adults: a systematic review and meta-analysis update. British Journal of Dermatology. 2018. 212 studies, 86 skin areas.
- Green M, Feschuk AM, Kashetsky N, Maibach HI. "Normal" TEWL: how can it be defined? A systematic review. Experimental Dermatology. 2022;31(10):1618-1631.
- Fluhr JW, Darlenski R, Surber C. Glycerol and the skin: holistic approach to its origin and functions. British Journal of Dermatology. 2008;159(1):23-34.
- Zettersten EM, Ghadially R, Feingold KR, Crumrine D, Elias PM. Optimal ratios of topical stratum corneum lipids improve barrier recovery in chronologically aged skin. Journal of the American Academy of Dermatology. 1997;37(3 Pt 1). Aged mice and 6 aged human volunteers.
- Ghadially R, Halkier-Sorensen L, Elias PM. Effects of petrolatum on stratum corneum structure and function. Journal of the American Academy of Dermatology. 1992;26(3):387-396. Human volunteers, acetone barrier disruption.
- PEPTIDES+ catalog, SpecKare E-GCu11 Solution efficacy test (supplier data): 5% lotion, 20 women aged 20 to 55, face; TEWL -17.82% at day 14, -27.91% at day 28, -31.37% at day 56 vs day 0, VapoMeter SWL5.
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure, or prevent any disease.
About the Author
Written by Kari Thomas, cosmetic formulator and founder of Skin Perfection.