## 1 Introduction  
In the United States, more than 6 million patients suffer from chronic wounds [1], while acute and chronic wounds affect around 1.5-2 million people in Europe [2]. Not only is the prevalence of wounds very high, their treatment is also costly and accounts for a significant proportion of the healthcare budget [2]. A Welsh study analyzed the cost factor of patients with chronic wounds. With an overall prevalence of chronic wounds of 6% in the population, the cost of wound care, comorbidities and complications amounted to 5.5% of total healthcare expenditure [3]. In the United States, chronic wounds are even listed as one of the main causes of morbidity and mortality [4]. This is one of the reasons why knowledge about the correct care of wounds is so relevant. As the range of wound dressings available is large, and choosing the right dressing is not a trivial matter, clinical staff must be trained accordingly. Ultimately, correct wound care is also a cost factor. The initial correct treatment of a wound saves money for the healthcare system and also accelerates the healing process for the patient [5]. Wound dressings can be divided into interactive, inactive and bioactive dressings [6]. Inactive wound dressings are characterized by their high absorption capacity and rather low cost factor. They are made of cotton or synthetic fibers. Interactive wound dressings fulfill several criteria. They should generate a sufficiently moist wound environment and a constant pH value. They are also supposed to absorb any toxic substances that are released. And they should prevent wound infections, be practical and enable simple and painless changing of the dressings. Interactive wound dressings include alignates, hydrofiber dressings, wound dressings containing silver, hydrogels, hydrocolloids, hydropolymer wound dressings, foams and gauzes. Bioactive wound dressings are reserved for special medical indications. They are mainly used in the treatment of chronic wounds, and predominantly in hospitals. These are skin substitutes such as autologous- skin, pig-skin or collagen-based wound dressings [6]. Wound dressings also differ in terms of their occlusive properties: dressings with a membrane overlay (such as dressings with an adhesive border), for example, are more occlusive than those without a membrane, such as compresses or plain foam dressings. However, how exactly the skin underneath a wound dressing changes has not yet been sufficiently investigated. Similarly, there is no established method for quantitative assessment, for example in the clinical testing of wound dressings, with regards to their occlusive effects. This study aims to investigate how transepidermal water loss (TEWL) and skin moisture change under different wound dressings as a result of topical therapy with the associated different occlusion. Different types of wound dressings are used in the medical treatment of wounds. The selection of the correct dressing depends on the cause of the skin damage, on the one hand, and on the determination of the degree of drainage and depth of the wound, on the other [4]. During treatment, attention must also be paid to the likelihood that the tissue is already colonized with pathogenic microorganisms and to the amount of necrotic tissue in the wound [7]. The degree of exudation also plays an important role in wound care. With an area of 1.4 to 2 m\({}^{2}\), the skin is the largest organ in the human body. It makes up about 15% of the human body weight and has a thickness of 1-2 mm [8; 9; 10]. It is built up in several layers. A distinction is made between two larger compartments: the dermis, whose functions are diverse and complex [11], and the overlying epidermis, which, among other things, fulfills barrier functions. Four further layers, the stratum corneum, stratum granulosum, stratum spinosum and stratum basale, in turn, form the structure of the epidermis [8; 9; 10]. The stratum corneum plays a special role in relation to the significance of the present study.