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TEWL – Transepidermal Water Loss Explained

TEWL (Transepidermal Water Loss) measures the amount of water that passively evaporates through the skin. It is a key marker of skin barrier function used in dermatology and cosmetic research.

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Things worth knowing about "TEWL"

TEWL (Transepidermal Water Loss) measures the amount of water that passively evaporates through the skin. It is a key marker of skin barrier function used in dermatology and cosmetic research.

What Is TEWL?

TEWL stands for Transepidermal Water Loss and refers to the passive evaporation of water through intact skin into the surrounding environment. This process occurs continuously and should not be confused with active sweating. TEWL is a well-established biophysical measurement parameter used in dermatology and cosmetology to assess the condition of the epidermal skin barrier.

Physiological Background

The outermost layer of the skin, the stratum corneum (horny layer), forms a semipermeable barrier that regulates water loss from the body. This barrier consists of dead skin cells called corneocytes, embedded in a lipid-rich matrix. When this structure is intact, TEWL values remain low. If the barrier is damaged or compromised, water loss increases measurably.

In healthy skin, normal TEWL values typically range between 5 and 15 g/m²/h, depending on body region, age, ambient temperature, and humidity.

Clinical Relevance

Elevated TEWL values indicate a compromised skin barrier and may be observed in a variety of conditions:

Atopic dermatitis (eczema): Genetically driven barrier defects, often linked to mutations in the filaggrin gene, lead to significantly elevated TEWL.
Psoriasis: Altered keratinocyte differentiation impairs the barrier function of the stratum corneum.
Contact dermatitis: Chemical or allergenic irritants damage the stratum corneum.
Ichthyosis: Genetic keratinization disorders substantially increase TEWL.
Aged skin: Declining lipid content in the stratum corneum with age results in higher TEWL values.
Newborns and premature infants: The skin barrier is not yet fully developed, leading to markedly elevated TEWL.

Measuring TEWL

TEWL is measured non-invasively using specialized devices called tewameters or evaporimeters. These instruments measure the water vapor gradient above the skin surface and calculate the rate of water evaporation. Two common measurement methods are used:

Open-chamber method: An open measurement chamber is placed on the skin; sensors at two different heights measure temperature and relative humidity to determine the evaporation gradient.
Closed-chamber method: A sealed chamber records the rise in humidity over a defined period of time.

To ensure reliable and reproducible results, standardized conditions must be maintained: a constant room temperature of approximately 20–22 °C, controlled relative humidity of around 40–60 %, no physical activity immediately before measurement, and a skin acclimatization period of at least 15–30 minutes.

TEWL in Cosmetic and Pharmaceutical Research

In the cosmetic and pharmaceutical industries, TEWL serves as an efficacy marker for skin care products, emollients, moisturizers, and topical drugs. Products that significantly reduce TEWL are considered to support and restore skin barrier function. Common ingredients that lower TEWL include:

Ceramides: Natural components of the lipid matrix of the stratum corneum.
Glycerol (glycerin): Attracts moisture and reinforces barrier function.
Urea: Increases water retention capacity of the stratum corneum.
Petrolatum and mineral oil: Create an occlusive layer on the skin surface, reducing evaporation.
Fatty acids (e.g., linoleic acid): Support the regeneration of the lipid lamellae in the barrier.

TEWL as a Diagnostic Marker

In clinical research and dermatology, TEWL is used as an objective, reproducible parameter to:

Quantify the severity of skin diseases.
Monitor treatment outcomes in dermatoses.
Evaluate the protective efficacy of gloves, barrier creams, or textiles in occupational medicine studies.
Assess skin maturation in newborns and premature infants.

References

Fluhr, J.W., Darlenski, R. & Surber, C. (2008). Glycerol and the skin: holistic approach to its origin and functions. British Journal of Dermatology, 159(1), 23–34.
Elias, P.M. (2005). Stratum corneum defensive functions: an integrated view. Journal of Investigative Dermatology, 125(2), 183–200.
Darlenski, R. et al. (2009). Non-invasive in vivo methods for investigation of the skin barrier physical properties. European Journal of Pharmaceutics and Biopharmaceutics, 72(2), 295–303.

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