TEWL reference values in healthy adults

Transepidermal water loss (TEWL) is the amount of water which passes from inside the human body through the skin layers to the outside. This diffusion cannot be observed directly so we use different measurement devices to detect it. Measurement of TEWL can be useful to identify healthy or diseased skin. Higher TEWL can be a sign of skin impairment, meaning the skin's protective barrier is damaged or not working properly, and therefore letting more water pass through. However, TEWL is affected by many factors such as temperature, humidity, age, gender, anatomical region (body part), skin temperature, measurement device and many other factors. Therefore, TEWL must be carefully interpreted and a "normal" TEWL does not exist. This systematic review and meta‐analysis, from Germany, aimed to find out TEWL reference estimates for healthy skin in adults by combining many different individual studies published in the last 60 years. The authors provided TEWL estimates for 86 skin areas from 212 studies in healthy adults. They found that TEWL is highly dependent on skin area and seems to show a symmetrical pattern between the right and left body sites. TEWL in the elderly seems to be generally similar or decreased compared with younger adults. The difference between TEWL estimates for different measurement devices seems to be minimal.