## 4 Discussion
Covering the skin (e.g., with wound dressings) increases skin moisture on the one hand, and on the other hand, increased TEWL values are also recorded when measured after removal of the occlusion [28; 29; 30]. A German study has already shown that TEWL values increased significantly after the application of epicutaneous plasters with sodium lauryl sulphate (SLS) in various concentrations (0.25%, 0.5%). This was demonstrated for incubation times of 12, 24 and 48 h [31]. Similar results were also shown in other studies [28]. However, only one type ofskin coverage was examined. Similar results could even be achieved with furred animal skin. In the examination of the stratum comeum of 10 healthy dogs, increased TEWL values were also associated with impaired skin barrier function [32]. The TEWL value is one of the most important measurable parameters for assessing the barrier function of the skin [25; 26; 28; 33; 34]. It represents the amount of condensed water that diffuses to the skin surface via the stratum comeum per unit of time [33]. It is a relevant but susceptible parameter. In the present study, increased TEWL values were measured on average across all test subjects for almost all wound dressings on the second day of the study. The only exceptions to this were Solvaline and Metalline. Both wound dressings were compresses. The mean measured daily difference values are only slightly negative, and could also have come about within the framework of acceptable intraindividual measurement variability. However, the nature of the wound dressings could also be responsible for the results. Both dressings can be used for wounds with low-to-moderate exudation. Most simple wound dressings are made of cotton. This material is characterized by the fact that it is soft, absorbent and hypoallergenic, and is therefore well tolerated by most people [35]. The high absorbency could explain why none of the wound dressings in the simple wound-dressings category showed a significant difference in TEWL between the two measurement days or between the respective preparation and the control group. It could be concluded that the proportion of water lost via the epidermis is absorbed by the preparations and that the accumulation of humidity under the wound dressing is lower and the TEWL is therefore not affected. Transparent dressings like Teagoderm, on the other hand, are only minimally absorbent. Their advantage is that their transparency allows for the monitoring of wound status. Although these polyurethane films are semi-permeable in nature, fluid collects underneath these dressings [35]. They therefore have a highly occlusive character, which fits the results of our study and explains the high TEWL and skin-hydration values, which were not only significantly higher on the second day, but also in contrast to the control site. All film dressings examined in the study are made up of different versions of Suprasorb P. The dressings are used for moderately exuding wounds. They are based on polyurethane foam and silicone, are bacteria- and waterproof, and also attempt to create a moist skin environment. Typical areas of application are superficial injuries, minor burns, ulcers and chronic wounds. Film dressings, therefore, share similar areas of application to foam wound dressings. They also consist of polyurethane but, unlike the transparent and film dressings, they have much thicker sheets and can absorb a higher amount of skin moisture [35]. In order to create an optimal healing environment for ulcers, a wound environment that is as moist as possible should be established [36]. Biatain dressings showed the highest mean daily differences in terms of skin hydration, while Allevyn products achieved the highest differences in terms of TEWL. The main component of both types of wound dressing is a hydrophilic polyurethane foam. Both wound-dressing manufacturers use a silicone-based adhesive layer, which contributes significantly to the occlusive character. These similarities with regard to the structure of the products could explain the findings.