Trans-epidermal water loss (TEWL)

Trans-epidermal water loss (TEWL) is the passive diffusion and subsequent evaporation of water vapor from within the skin, across the stratum corneum, into the surrounding air. It is expressed as a flux (grams of water per square meter of skin per hour, g/m²/h) and serves as a widely accepted, noninvasive index of epidermal barrier integrity. In general, lower TEWL indicates a more competent barrier, whereas elevated TEWL reflects impaired barrier function.

Why it matters

Because the stratum corneum is the primary barrier limiting outward water movement, TEWL is tightly linked to the organization and function of its corneocytes and lipid matrix. Many common conditions that disturb this architecture—such as atopic dermatitis, contact dermatitis, psoriasis, or acute and chronic wounds—show increased TEWL. In research and clinical practice, TEWL helps:

• Objectively assess barrier function in health and disease

• Track disease activity or recovery (e.g., after topical therapy, phototherapy, or procedural interventions)

• Evaluate the mildness and barrier effects of skincare and personal-care products

• Monitor occupational skin exposure and early barrier compromise in the workplace

• Guide special populations care, notably preterm neonates, whose immature skin has high water loss

How it is measured

Modern instruments infer TEWL from the water vapor gradient immediately above the skin. Three main approaches are used:

• Open-chamber (evaporimetry)

• Unventilated-chamber

• Condenser-/closed-chamber methods

Although devices differ in design and environmental susceptibility, all are sensitive to microclimate. Robust technique therefore matters: subjects typically acclimatize for 15–30 minutes in controlled conditions (about 20–22°C, 40–60% relative humidity), the test site is exposed to ambient air for several minutes, and confounders like recent washing, topical products, vigorous activity, or sweating are minimized. Recording the anatomical site, instrument type, and ambient conditions alongside TEWL values improves interpretability and reproducibility.

Typical values and variability

There is no single universal “normal” TEWL because values vary substantially by body site and context. Large meta-analyses in healthy adults report site-specific ranges from roughly 2.3 g/m²/h (e.g., breast skin) up to around 44 g/m²/h (e.g., axilla). On commonly tested sites such as the volar forearm, typical values in healthy adults are often in the mid–single digits to low teens g/m²/h, with modest inter-individual variability. Age, anatomical site, ambient conditions, and measurement method contribute to differences between studies, underlining the importance of standardized protocols.

Key usage areas

• Dermatology: Elevated TEWL is a hallmark of conditions with barrier disruption; it is useful on lesional and nonlesional skin to quantify impairment and to follow response to therapies such as topical corticosteroids, emollients, or phototherapy.

• Cosmetic science and product substantiation: TEWL helps substantiate claims such as “supports the skin barrier,” “is gentle/mild,” or “reduces irritation,” and is used to screen ingredients that influence barrier function.

• Occupational health: Repeated wet work, detergents, and irritants can raise TEWL before visible dermatitis develops, enabling early preventive action.

• Neonatology: Preterm infants exhibit high insensible water loss; TEWL monitoring informs incubator humidity/temperature strategies and fluid/electrolyte management.

• Wound and burn care: Burned or scarred skin generally shows higher TEWL; serial measurements can complement clinical assessment of barrier restoration.

Practical considerations and limitations

• TEWL reflects water vapor flux, not stratum corneum hydration; combining TEWL with corneometry (hydration) or other bioengineering measures yields a fuller picture.

• Sweating can confound readings; measurements should be taken at rest under thermoneutral conditions and, where possible, on sites with minimal eccrine activity.

• Because absolute values depend on device type, site, and environment, within-subject comparisons over time and careful standardization are often more informative than cross-study numerical comparisons.

Sources

• Alexander H, Brown S, Danby S, Flohr C. Research Techniques Made Simple: Transepidermal Water Loss Measurement as a Research Tool. Journal of Investigative Dermatology (2018). https://pubmed.ncbi.nlm.nih.gov/30348333/

• EEMCO guidance for the assessment of transepidermal water loss in cosmetic sciences. Skin Pharmacology and Applied Skin Physiology (2001). https://pubmed.ncbi.nlm.nih.gov/11316970/

• Kamann S, et al. Transepidermal water loss in healthy adults: a systematic review and meta-analysis update. British Journal of Dermatology (2018). https://academic.oup.com/bjd/article/179/5/1049/6732543

• Park JH, et al. Devices measuring transepidermal water loss: a systematic review of measurement properties. Skin Research and Technology (2023). https://pmc.ncbi.nlm.nih.gov/articles/PMC9907714/

• Kearney GD, et al. Comparison of Hydration Index, Percent Hydration, and Trans-Epidermal Water Loss Measurements. Annals of Work Exposures and Health (2022). https://academic.oup.com/annweh/article/66/7/907/6576506

• CDC/NIOSH guidance excerpt on TEWL measurement setup and acclimatization (summarizing EEMCO). https://stacks.cdc.gov/view/cdc/32597

• Kelleher MM, et al. Newborn transepidermal water loss values: a reference dataset. Pediatric Dermatology (2013). https://pubmed.ncbi.nlm.nih.gov/23458265/

• Schneider JC, et al. Transepidermal water loss measured in burn scars. Burns (2016). https://pubmed.ncbi.nlm.nih.gov/27233677/

• Bhat YJ, et al. Transepidermal Water Loss in Psoriasis: A Case-control Study. Indian Dermatology Online Journal (2019). https://pubmed.ncbi.nlm.nih.gov/31149569/

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