Disturbance of the epidermal barrier function, which is maintained mainly by cor-neocytes and stratum corneum lipids, occurs with increased transepidermal water loss (TEWL). This phenomenon occurs early in irritant reactions and precedes visible skin changes. Accordingly, the TEWL is a very sensitive parameter and has become one of the most important bioengineering methods. Measurement of the TEWL has been used in several studies on the vulvar skin, mainly to quantify irritant contact dermatitis (2,23,24). Different methods for TEWL measurements are available. In general, the more common open-chamber devices, such as the Tewameter® (Courage & Khazaka, Cologne, Germany), and the Evapori-meter® (Servo Med, Stockholm, Sweden) have become much more established, as compared to the closed-loop systems (25). The open-chamber methods utilize a cylindric probe that is integrated in a hand piece and equipped with a pair of sensor units (hygro sensors coupled with thermistors). When placed onto the skin, the probe measures the continuous water vapor gradient from the skin surface. Ideally, the probe should be handled in a horizontal plane position, which is difficult to achieve on the vulvar skin. In contrast, the closed system is designed to be applicable in different positions (25). However, the main drawback of this method is the tendency to occlude the skin, thus causing artifacts. Furthermore, continuous measurements are not possible with this method (26).
Baseline values of the TEWL were found to be significantly higher on the vulva compared to the forearm skin (27). Age-related differences were observed between pre- and post-menopausal women, as the TEWL was significantly lower in postmenopausal compared to premenopausal women (28). In general, significant intra- and inter-individual variations of the TEWL are well known, not only in the genital area. As the water evaporation from the skin is also influenced by thermoregulative requirements of the individual and sweat gland activity, it is of utmost importance to exclude disturbing variables by thoroughly following the guidelines of the European Society of Contact Dermatitis on the measurements of TEWL (26). TEWL can only be measured after an appropriate waiting period for the postocclusion water loss to subside (9).
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