The importance of transepidermal water loss (TEWL) for skin health

Introduction: what is TEWL, and why does it matter?

Transepidermal Water Loss (TEWL) is the skin’s natural mechanism for regulating hydration. Water passively moves from deeper skin layers to the surface, where it evaporates. This process is crucial in maintaining skin homeostasis, ensuring the barrier remains functional and resilient. Unlike sweating, which is an active response to heat or stress, TEWL is a constant, passive occurrence influenced by factors such as skin health, environmental conditions, and individual biology.

TEWL is widely regarded as a key indicator of skin barrier integrity. TEWL remains stable when the barrier functions optimally, preventing excessive moisture loss. However, when the barrier is weakened—due to aging, harsh environmental exposure, or skin disorders—TEWL increases, leading to dehydration, irritation, and increased sensitivity. Monitoring TEWL is essential in dermatology, skincare formulation, and clinical research, as it provides insights into skin health and how different products or conditions influence the barrier.

This article will explore TEWL’s role in skin physiology, the factors influencing its levels, and how targeted skincare strategies can help regulate it. We will also examine how different areas of the body exhibit varying TEWL rates and why a tailored approach to skincare is necessary to maintain hydration and barrier strength.

Understanding TEWL and its role in skin health

The science behind TEWL

Transepidermal Water Loss (TEWL) is a natural physiological process that helps maintain skin hydration by allowing water to passively move from the deeper layers of the epidermis to the surface. Since the outermost layer of the skin (the stratum corneum) is not vascularized, it relies on this continuous water movement to stay hydrated. However, excessive TEWL can indicate a weakened skin barrier, leading to dryness, irritation, and increased sensitivity. For this reason, TEWL is widely used in dermatology and skincare research to assess skin conditions such as atopic dermatitis, psoriasis, and xerosis.^1,2,3

TEWL is influenced by multiple intrinsic and extrinsic factors, including:

Age: While some studies suggest that TEWL decreases with age due to reduced gland activity and changes in skin lipids, others indicate that those changes have little impact on TEWL.^1,2
Genetics: Genetic variations, particularly mutations in genes linked to skin barrier function (such as filaggrin), can lead to increased TEWL, making individuals more prone to conditions like eczema.¹
Skin health and alterations of the skin barrier function (such as contact dermatitis, wounds, burns, etc.)³
Environmental Conditions^1,2:

Temperature: High temperatures accelerate water evaporation, increasing TEWL, while cold environments slow it down.
Humidity: Low humidity levels cause more significant water loss from the skin, whereas high humidity helps retain moisture.
Air Movement: Wind and air circulation can enhance evaporation, leading to higher TEWL rates.
Others: Sun exposure, atmospheric pollution, smoking status.
Skincare Habits^1,3:

Cleansing: Frequent washing, especially with harsh detergents, strips the skin of its natural lipids, weakening the barrier and increasing TEWL.
Moisturization: Occlusive ingredients in skincare products, such as lanolin or petrolatum, help reduce TEWL by forming a protective layer that locks in moisture.
Exposure to chemicals or mechanical damage as a result of work.
Use of protective clothing, such as gloves and UV-blocking fabrics, or the application of sunscreen to minimize environmental damage.

Understanding these factors is essential for developing strategies to maintain skin hydration and barrier integrity through targeted skincare, environmental adjustments, or dermatological treatments.

The skin barrier and its function

The stratum corneum, the outermost layer of the skin, acts as the primary barrier against excessive water loss. It comprises corneocytes (flattened, non-living skin cells) embedded in a lipid matrix, often likened to a « brick and mortar » structure, where the corneocytes are the bricks and the lipid layers form the mortar. This complex organization maintains hydration and protects against external irritants.¹

Water retention in the skin depends on the balance between hydration and TEWL. The stratum corneum must retain enough moisture to remain flexible and resilient while preventing excessive water loss that could lead to dehydration and impaired function. When this barrier is disrupted—due to external factors like chemical exposure, friction, or UV damage—TEWL increases, often leading to visible signs of dryness, irritation, or even inflammatory skin conditions.³

TEWL varies significantly across different anatomical regions of the body. Research indicates that areas with a thinner epidermis, such as the forearm, tend to have lower TEWL, whereas areas with more sweat glands, such as the palms, soles, and forehead, exhibit higher TEWL levels.⁴ This is partly due to the sebaceous and sweat gland distribution—areas with a high concentration of sweat glands generally have more active water flux.³

A meta-analysis of TEWL across different body sites confirmed that the highest TEWL values are found in the armpit and palms, while the lowest are recorded on the breast and thigh.²These findings highlight the importance of considering anatomical site variations when formulating moisturizers, as different regions of the body have distinct physiological characteristics that influence water loss.

Understanding TEWL and its role in skin health allows skincare professionals and researchers to develop targeted strategies to maintain optimal hydration and barrier function. Whether through improved skincare formulations, environmental controls, or personalized skincare regimens, managing TEWL effectively ensures skin remains healthy, resilient, and well-hydrated.

How skincare formulations impact TEWL

The integrity of the skin barrier and its ability to retain moisture are profoundly influenced by the formulations used in skincare products. Various ingredients in moisturizers and skin treatments significantly modulate TEWL. The effectiveness of a formulation in controlling TEWL depends on its ability to reinforce the skin barrier, attract moisture, and reduce water loss.

The role of skincare ingredients in TEWL regulation

Occlusives: preventing water loss^5,6,7

Occlusive agents are fundamental in reducing TEWL by forming a hydrophobic barrier on the skin’s surface, significantly minimizing water evaporation. Petrolatum, for instance, is among the most effective, reducing TEWL by over 98%. However, while these ingredients help retain moisture, highly occlusive formulations can create a thick, greasy layer that some users find uncomfortable for daily use. Additionally, excessive occlusion traps sebum and impurities, potentially leading to clogged pores and breakouts, particularly in acne-prone skin. To balance hydration and breathability, partially occlusive ingredients like lanolin and silicones such as dimethicone reduce TEWL by 20-30% and balance occlusion with breathability to maintain skin hydration without compromising its natural functions.

Humectants: enhancing hydration^5,6,7

Humectants attract water to the stratum corneum, primarily from deeper skin layers and, to a lesser extent, from the surrounding environment. Ingredients like glycerol and urea help improve hydration and support the skin barrier, with urea showing particular benefits in conditions such as atopic dermatitis and ichthyosis. However, humectants alone can inadvertently increase TEWL if not paired with an occlusive, as they pull moisture toward the surface without providing a barrier to prevent evaporation.

While technically not a humectant, lanolin exhibits exceptional water-binding properties, retaining up to 400% of its weight in water. This makes it highly effective in maintaining skin hydration, particularly in dry conditions where external humidity is low and traditional humectants may be less effective.

Emollients and lipid replenishers: supporting barrier function^5,6,7

Emollients such as silicones, esters, and fatty acids help maintain skin texture, smoothness, and flexibility by filling in gaps between corneocytes. They also reinforce the skin barrier, reducing TEWL and preventing excessive moisture loss, which helps keep the skin hydrated and resilient.

While emollients primarily improve skin feel, and hydration, lipid replenishers go a step further by restoring the essential lipids needed for a fully functional barrier. These natural lipids, including ceramides and sterols, are crucial for barrier function and hydration retention. Lanolin, for example, functions as both an emollient and a lipid replenisher, as it contains sterols and fatty acids structurally similar to those in human skin. This allows it to integrate into the skin’s lipid layers, strengthening the barrier while helping to retain moisture and prevent dehydration.

The impact of formulation types on TEWL^5,6,7

The type of moisturizer formulation plays a crucial role in regulating TEWL, as different textures and compositions influence how water is retained or lost from the skin.

Water-based formulations – Hydration without occlusion

Water-based formulations like serums and gels provide immediate hydration by delivering humectants such as glycerin, hyaluronic acid, and urea. These ingredients attract moisture to the skin, increasing hydration levels in the short term. However, because these formulations contain little to no occlusives, they do not prevent moisture from escaping. This makes them practical for a temporary hydration boost but insufficient for long-term TEWL prevention. Water-based products work best in humid environments or as a first step before applying a more protective product.

Emulsions – A balanced approach to TEWL prevention

Emulsions like lotions and creams combine water and oil phases, offering a more balanced approach to hydration and TEWL prevention. Lotions (oil-in-water), with their high water content and lightweight feel, provide mild occlusion, making them ideal for normal or combination skin. Creams (water-in-oil), which have a higher oil content, create a stronger barrier against moisture loss, making them more suitable for dry or compromised skin. These formulations are generally more effective than serums and gels in reducing TEWL, especially in colder or drier climates, where additional protection is needed to maintain skin hydration.

Oil-based and anhydrous formulations – Maximum TEWL protection

For maximum TEWL prevention, oil-based and anhydrous formulations such as ointments, balms, and oils provide the most protection. Ointments, which contain high concentrations of occlusives like petrolatum or lanolin, form a dense barrier over the skin, significantly reducing water loss. Balms and oils, while slightly less occlusive than ointments, still help restore lipids and reinforce the skin barrier, making them particularly beneficial for severely dry, irritated, or environmentally exposed skin, such as hands subjected to cold weather or frequent washing.

Formulation strategies for harsh climates

Cold and dry environments: need for occlusive-heavy formulations^8,9

Cold and dry climates pose a significant challenge to skin hydration, as low humidity and indoor heating accelerate TEWL. Prolonged exposure to these conditions weakens the skin barrier, increasing moisture loss and heightening the risk of dryness, roughness, and irritation. Studies show that extended time in low-humidity environments can lead to a compromised barrier, making the skin more prone to sensitivity and even dermatitis.

For cold and dry conditions, formulations should be rich in occlusives like petrolatum, lanolin, or mineral oil and lipid replenishers such as lanolin and ceramides to strengthen the barrier. Oil-in-water emulsions (creams) or even oil-based formulas offer superior protection by sealing in moisture and preventing excessive TEWL.

Hot and humid climates: lightweight hydration and barrier support⁸

Hot and humid environments pose a unique challenge, as they trigger increased sweat production while simultaneously accelerating TEWL. Research shows that while high humidity initially boosts hydration, prolonged exposure leads to increased water evaporation, dehydrating the skin. Moreover, excess sebum and sweat can disrupt the barrier function, making the skin prone to irritation.

Lightweight hydration and barrier-supportive formulations are ideal for such conditions. Humectants like glycerin, urea, and hyaluronic acid help retain moisture without feeling heavy on the skin. Breathable occlusives like lanolin provide a barrier that prevents excessive water loss without clogging pores.

TEWL in exposed areas: hands, face, and lips

Exposed areas of the body are particularly vulnerable to high TEWL due to their frequent interaction with environmental stressors. These regions are more prone to dehydration, barrier dysfunction, and external damage, making their TEWL regulation crucial for maintaining healthy skin.

TEWL and hands

Why hands lose moisture⁴

The skin of the hands faces constant challenges due to its unique physiological characteristics, repeated washing, and exposure to hand sanitizers. Unlike most of the body, the palms lack sebaceous glands, meaning they do not produce sebum—the natural lipid-rich substance that helps retain moisture and protect the skin barrier. Instead, the palms rely on sweat glands, which are present in high density and primarily function to regulate temperature and improve grip rather than provide lasting hydration.

Studies show that the palms have significantly higher TEWL values than the forearm, with the hand-to-arm TEWL ratio ranging from approximately 6:1 to 8:1. This suggests that the palms’ structural ability to retain moisture is much weaker, making them particularly vulnerable to dehydration and irritation.

In addition to these intrinsic factors, frequent washing with soap, particularly those containing surfactants such as sodium lauryl sulfate (SLS), further disrupts the skin’s lipid barrier, leading to increased TEWL. Similarly, alcohol-based hand sanitizers, while effective against pathogens, accelerate water loss by dissolving the skin’s protective lipid matrix.

Because the hands do not produce sebum and rely only on sweat for moisture, these external aggressors rapidly deplete natural moisturizing factors (NMFs), leading to dry, cracked, and irritated skin. This is common among healthcare workers, people in cold climates, and individuals whose jobs require frequent hand hygiene.

Hand creams: how to formulate for optimal protection^4,7

Hand creams should combine occlusives, humectants, and lipid replenishers to provide adequate hydration and barrier repair. Research shows that this multi-layered approach is more effective than relying on a single ingredient type. Occlusives like petrolatum, dimethicone, and lanolin prevent water loss, humectants such as glycerin and urea attract moisture, and lipid replenishers like ceramides, cholesterol, and natural oils restore the skin barrier. The drier or more damaged the hands, the richer and more occlusive the formulation should be to provide deeper hydration and protection.

The frequency of application also plays a critical role in mitigating TEWL-related damage. Studies suggest using a hand cream immediately after washing or sanitizing can significantly reduce moisture loss. Formulations with fast-absorbing properties are particularly beneficial for individuals who need to maintain hand hygiene throughout the day.

TEWL and face¹⁰

The unique challenges of facial skin

Facial skin is the most exposed part of the body, making it highly vulnerable to environmental factors that can accelerate transepidermal water loss. Unlike other body areas, facial skin has a thinner stratum corneum, particularly around the eyelids, making it more permeable to external aggressors.

Environmental factors such as UV radiation, fluctuating humidity, temperature changes, and frequent washing with harsh cleansers strip away essential lipids and compromise the skin barrier, leading to increased TEWL. Seasonal variations also impact facial TEWL levels—studies show that in winter, the skin experiences higher TEWL rates and lower hydration levels, contributing to irritation and inflammation.

Another challenge is that facial skin has a higher epidermal turnover rate, completing a renewal cycle in just 10 days compared to 14 days for other body areas. This rapid renewal process means that the skin barrier is constantly undergoing changes, making consistent protection essential.

High TEWL on the face is directly linked to skin dryness, irritation, and sensitivity. Research shows that when the stratum corneum loses excessive moisture, it triggers inflammatory reactions, leading to visible redness and irritation. Furthermore, UV exposure not only increases TEWL but also depletes ceramides—key lipids essential for maintaining barrier integrity.

Best ingredients for reducing TEWL on the face

Due to its high susceptibility to TEWL, facial skin requires a balanced combination of ingredients to maintain hydration while preserving breathability:

Occlusives like petrolatum, lanolin, and shea butter form a protective layer to minimize moisture loss.
Humectants: Glycerin, hyaluronic acid, and urea attract and retain water within the skin.
Barrier Repair Lipids: Ceramides, cholesterol, and free fatty acids help restore and strengthen the skin’s natural lipid matrix.

However, overly rich or comedogenic formulations can trap sebum and impurities, potentially leading to irritation, clogged pores, and acne flare-ups.

TEWL and lips¹¹

Why the lips are prone to TEWL

Unlike most of the skin, lips lack sebaceous glands and have a thinner stratum corneum, which reduces their ability to retain moisture. Studies show that lips exhibit significantly higher TEWL values than the cheeks, making them prone to dryness, roughness, and cracking.

Additionally, the composition of lip skin lipids differs from other areas of the body. The lips contain lower levels of ceramides—critical components for maintaining a strong skin barrier—and have a higher percentage of ceramide subclasses associated with a weaker barrier function. This means that even under normal environmental conditions, the lips are predisposed to dehydration and require extra care to maintain moisture levels.

The role of occlusivity in reducing TEWL

Since lips naturally have a high TEWL rate, increasing occlusivity is a primary strategy for preventing moisture loss. Most lip balms create a protective layer that locks in hydration and reduces evaporation.

A study assessing different lip balm formulations found that highly occlusive formulas significantly improved lip hydration, roughness, and wrinkle scores over four weeks. In this study, subjects using a highly occlusive lip balm experienced smoother texture, increased hydration, and plumber lips.

Notably, occlusivity alone—without specialized care agents—was enough to enhance hydration and appearance, underscoring the importance of well-formulated lip balms.

Conclusion

Transepidermal Water Loss is a key factor in skin hydration and barrier function. While essential for maintaining skin balance, excessive TEWL leads to dryness, irritation, and increased sensitivity. Effectively managing TEWL requires a targeted approach, combining occlusives, humectants, emollients, and lipid replenishers to lock in moisture, attract hydration, and reinforce the skin barrier.

Different body areas, such as the hands, face, and lips, have varying TEWL levels and require tailored skincare. Hands, frequently exposed to washing and external stressors, benefit from richer, occlusive formulations. Facial skin, being thinner and more permeable, needs a balance of hydration and breathability. Lips, with naturally high TEWL, require strong occlusion to prevent chapping and dehydration.

By understanding TEWL and adapting formulations accordingly, skincare professionals can develop more effective products that protect, hydrate, and strengthen the skin barrier across different conditions and needs.

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