56 TESTING
Measuring skin barrier: key for many applications
n C. Uhl, G. Wiora, D. Khazaka – Courage & Khazaka, Germany
When the first objective skin measurement systems were developed in the 1980s, the measurement of the Transepidermal Waterloss (TEWL) was among the very first. Until today, it has remained one of the most important measurements for the assessment of skin health. Our skin is a protective barrier against
environmental influences. It continuously releases water which is part of its metabolism. This normally imperceptible process is called Transepidermal Water Loss (TEWL). It is based on complex physical diffusion processes taking place in and above the skin. Molecules of water and air move in a chaotic way and transfer energy between each other and to the environment through collisions. The difference in concentration between the skin surface and the surrounding atmosphere is the driving force that turns the random movement of the particles into a directed redistribution. The TEWL is a measure for this gradient,
expressed in g/m²/h. It is a good indicator for the quality of the skin as the outermost barrier of the body. There are different methods on the
market to assess this parameter. One is called “open chamber measurement” where the unobstructed diffusion in real time takes place in a hollow cylinder. There are also “closed chamber” systems on the market using a cold plate to collect the water in the chamber (real time measurement) or using a short measurement time and extrapolation for a TEWL result. Until today, the “open chamber” is the
most used method. A large number of studies with this measurement method over the years proves this fact. In a recent guideline for in vivomeasurement of water in the skin from the EEMCO group the “open chamber” measurement of the Tewameter®
was mentioned as the “still
preferred techniques to measure the water balance in the skin”.1 The C+K Tewameter has always
operated based on the “open chamber” measurement. It assesses the gradient of
PERSONAL CARE EUROPE Figure 1: Tewameter® TM 300 with 2 sensor pairs, the latest Tewameter® pairs gaining 15 times more information.
water molecules between the skin surface and the ambient surrounding by temperature and relative humidity sensor pairs. Whereas the predecessor model
Tewameter TM 300 featured two pairs of sensors, with the new Tewameter TM Hex, sixty sensors (30 pairs) for temperature and relative humidity are embedded in the inner wall of the chamber. These sensors are continuously
recording a massive amount of data on the evaporation without influencing the micro environment of the skin. With this high data volume for each
single TEWL measurement value, the probe acts like a camera which “sees” the temperature and humidity distribution inside the diffusion tube, thus giving extremely accurate, reproducible and quick results. In addition, through the dense local and
temporal resolution provided by the measurement, precise knowledge is available for the areas right outside probe: skin surface and ambience. Thus, the calculation of new, exciting parameters is possible which may give interesting insights in several research fields. 2
Local Skin Energy Balance One promising new parameter is the Local Skin Energy Balance describing the heat
flow from the skin to the environment. Skin is constantly emitting energy in two ways: Through diffusion of warm air molecules over the skin surface and through evaporation cooling. For the first time, these two can be recorded independently during a TEWL measurement and describe collectively the local energy balance of the skin. The measured values are expressed in W/m². The result ranges from a few W/m² for skin sites like the inner forearm up to 100 W/m² and more for areas such as the palms of the hands, for example. Typically, the heat loss by evaporation cooling is the dominant effect. Humans under normal conditions have a
basal metabolic rate of approx. 30 to 90 W and a body surface of approx. 2 m². Therefore, the average total heat loss is approx. 15-45 W/m², depending on conditions, age, gender and measured skin site it can be lower or higher.3
TEWL Under standard ambient conditions, a healthy skin barrier is characterised by a moderate Transepidermal Water Loss. As soon as the barrier function of the skin is slightly damaged, the water loss will increase - even with the smallest damages imperceptible to the human eye. TEWL is an important parameter in
dermatological basic research since several September 2020
TM Hex features 30 sensor
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