TEWL, Barrier Function and Formulation Strategy

Let’s stir up some magic in the lab with today’s hot topic: TEWL, the skin barrier function and formulation strategy, and why understanding these three ideas can completely change the way you develop moisturisers, serums, cleansers and barrier-focused skincare products!

If you spend any time reading skincare marketing, supplier presentations or trend reports, you will quickly come across the phrase skin barrier. You will also eventually meet another term that sounds technical but is actually incredibly useful for founders to understand: TEWL, or transepidermal water loss.

TEWL helps explain why some products feel comforting but do not deliver long-term skin support. It helps explain why some cleansers leave the skin tight and why some moisturisers build genuine loyalty. It also helps explain why barrier-focused skincare has become such a major category for modern beauty brands.

In this article, we are going to unpack what TEWL means, how it relates to barrier function, why it matters so much in skincare formulation, and how a thoughtful formulation strategy can support skin comfort, hydration and resilience in a much more meaningful way.

What Is TEWL in Skincare?

TEWL stands for transepidermal water loss. In simple terms, it refers to the water that passively escapes from the skin into the environment.

This is a completely normal process. Skin is not supposed to be a sealed plastic surface. Some water naturally moves outward and evaporates. The problem begins when too much water is lost too easily. That is when the skin may begin to feel dry, tight, uncomfortable or more reactive.

This is why TEWL matters so much in skincare. It gives us a way to think about how well the skin is holding onto its moisture. When the skin barrier is functioning well, TEWL stays better controlled. When the skin barrier is compromised, TEWL tends to rise.

That means a product designed to support the skin barrier is often, directly or indirectly, a product designed to help reduce excessive TEWL.

How TEWL and Barrier Function Are Connected

The outermost layer of the skin, often simplified as the skin barrier, helps regulate what stays in and what stays out. It is made up of skin cells and a lipid matrix that helps hold everything together. When this outer structure is in good shape, the skin does a better job of maintaining hydration and protecting itself from external stressors.

When that structure becomes disrupted, water escapes more easily. That increase in water loss is what TEWL is capturing as a concept.

So when founders hear about a damaged or weakened skin barrier, TEWL is part of the reason the skin feels different. The customer may notice tightness, flaking, sensitivity, stinging or visible dryness, but underneath that experience is often a barrier that is no longer controlling water loss as effectively as it should.

This is exactly why TEWL and barrier function belong in the same conversation. One helps explain the state of the skin, and the other helps explain the consequence.

Check our blog post on Understanding the Skin Barrier to understand more about it!

What Increases TEWL?

Many everyday factors can increase transepidermal water loss, which is one reason barrier-supportive skincare has become so relevant.

Harsh cleansing is one of the biggest contributors. If the cleansing system strips away too much of the skin’s natural protective material, the skin may feel fresh for a moment but more vulnerable afterwards.

Over-exfoliation is another major factor. Acids, physical exfoliants and overuse of resurfacing products can all disrupt the outer layers of the skin when used too aggressively or too frequently.

Retinoids, if introduced too quickly or combined poorly, can also increase skin stress and contribute to a compromised-feeling barrier.

Environmental factors matter too. Cold weather, wind, dry indoor heating, low humidity and UV exposure can all make it harder for the skin to maintain its moisture balance.

Then there is hot water too: washing with hot water increases the permeability of the skin and dissolves sebum more effectively than lukewarm water, leaving the barrier compromised.

And finally, there are biological and internal factors, such as aging, the circadian rhythm, inflammatory condition (eczema, psoriasis, seborrheic dermatitis) high cortisol levels, etc.

This is where founders need to think strategically. TEWL is not only a scientific measurement. It is also a real-world product design issue.

The Three Big Formulation Levers: Humectants, Emollients and Occlusive Support

When designing products with TEWL and barrier function in mind, three broad formulation levers matter again and again: humectants, emollients and occlusive or semi-occlusive support.

Humectants help attract and hold water. They are essential for giving the skin access to moisture and improving the feeling of hydration. But humectants alone are rarely the whole answer in a barrier-focused product.

Emollients help soften and smooth the skin. They improve skin feel, reduce roughness and can help make the skin surface feel more supple and comfortable.

Occlusive or semi-occlusive ingredients help reduce water loss by creating a protective layer that slows evaporation. Not every product needs to feel heavy or greasy to perform this role. The key is not maximal occlusion in all cases, but the right level of support for the target skin type and product purpose.

A strong barrier-supporting formula often uses all three approaches in a balanced way. 

TEWL, Sensitive Skin and Sensitised Skin Often Overlap

When skin becomes sensitive, reactive or sensitised, increased transepidermal water loss is often part of the picture. That does not mean TEWL is the only issue, but it often helps explain why the skin feels less comfortable, less resilient and more vulnerable.

This is why so many products positioned for sensitive skin are, in effect, barrier-support products. They aim to reduce discomfort, improve resilience and help the skin maintain a healthier moisture balance.

For you, this means TEWL is not a niche technical concept. It is directly relevant to some of the most commercially important skincare categories on the market today.

What Claims Make Sense in TEWL and Barrier-Focused Skincare

You may be able to support claims around hydration, barrier support, reducing the feeling of dryness, improving skin comfort, helping protect against moisture loss or supporting the skin barrier, depending on your formula and testing. But strong claims require strong substantiation. If you want to talk directly about reduced transepidermal water loss, you need an appropriate testing pathway behind that claim.

This is why many brands choose consumer-friendly language such as barrier-supporting, comfort-restoring, moisture-sealing or hydration-protecting rather than immediately reaching for more technical wording.

That said, education on TEWL still matters because it helps ensure the formula story is honest. You understand what the product is really trying to achieve, even if the final front-of-pack language is simplified.

For more info on claims compliance, re-read our blog post on How to Choose the Right Claims for Your Product!

Final Thoughts: TEWL Helps You Build Better Skincare From the Start

TEWL may sound technical at first, but once you understand it, it becomes one of the most practical ideas in skincare product development.

It helps explain why the skin feels dry, tight, reactive or less resilient. It helps connect hydration to barrier function. It helps founders see why some formulas create only a temporary soft feel while others genuinely support the skin over time. And it gives you a clearer framework for developing cleansers, moisturisers and barrier-focused products that actually make sense.

For cosmetic formulators like you, learning about TEWL helps you ask better questions, write better briefs, choose smarter claims and build more meaningful products for your audience.

If you want support turning barrier-focused ideas into retail-ready skincare with strong formula logic, elegant textures and clear market positioning, my lab can help you bridge that gap between skin science and founder-friendly product development.

Here’s to formulas that work and brands that thrive!

From my lab to yours,

Rose