- Transepidermal water loss (TEWL) is an established parameter in skin and wound research
- Obtaining accurate TEWL measurements in clinical research is challenging
- Interpretation should focus on changes over time instead on single estimates
The skin is a layered structure performing a multitude of essential tasks. One of this task is the protection from drying out, thus enabling human life on dry land. The most important skin layer providing this inside-out water barrier is the stratum corneum. Nevertheless, small amounts of water continuously diffuse from the inside to the outside which is called transepidermal water loss (TEWL). This flux density is expressed in g/m2/h. TEWL is widely regarded as one of the most important parameters characterizing the skin barrier integrity. Elevated TEWL is usually associated with skin barrier impairments, whereas low TEWL is considered as an indicator for skin barrier integrity. Today, TEWL is measured and reported in many different areas in dermatology, skin and wound research and hundreds of papers reporting TEWL estimates have been published. However, TEWL measurement in clinical research and practice is extremely challenging, because it cannot be measured directly. All possible confounders need be controlled to obtain accurate and error-free results (Rogiers 2001). Even placing a probe onto the skin surface influences the TEWL. If the epidermis is severely compromised or even absent TEWL is not defined. Appropriate interpretation of TEWL readings is also challenging because a ‘normal’ TEWL does not exist, values differ substantially even between adjacent skin areas, and the clinical relevance is sometimes not clear (Kottner et al. 2013, Hahnel et al. 2017). Therefore, changes of TEWL over time of the same skin area seem to provide much more useful information than single or comparative estimates.
Hahnel E, Blume-Peytavi U, Trojahn C, Dobos G, Stroux A, Garcia Bartels N, Jahnke I, Lichterfeld-Kottner A, Neels-Herzmann H, Klasen A, Kottner J. The effectiveness of standardized skin care regimens on skin dryness in nursing home residents: A randomized controlled parallel-group pragmatic trial. Int J Nurs Stud. 2017;70:1-10.
Kottner J, Lichterfeld A, Blume-Peytavi U. Transepidermal water loss in young and aged healthy humans: a systematic review and meta-analysis. Arch Dermatol Res. 2013;305(4):315-23.
Rogiers V; EEMCO Group. EEMCO guidance for the assessment of transepidermal water loss in cosmetic sciences. Skin Pharmacol Appl Skin Physiol. 2001;14(2):117-28.