## 1 Introduction  
Whole-body cryotherapy (WBC) is defined as the technique of extreme cooling of the body (below \(-\)100 \({}^{\circ}\)C) for a short period (1-3 min) to induce a physiological response to cold [1]. The term cryostimulation refers to the use of cold exposure among healthy subjects(e.g., athletes); cryotherapy, on the other hand, refers to the use of cold in medical treatment including the management of injuries, inflammation, and other disorders [2]. Cryogenic temperatures have been successfully used in patients with rheumatoid arthritis [3], multiple sclerosis [4], fibromyalgia [5], and more recently, adjunctively in the treatment of obesity [6; 7; 8]. The effects of cryotherapy on improving mood and mental state are also indicated [9; 10; 11]. Additionally, growing evidence suggests the potential use of low temperatures in dermatology and cosmology [12; 13; 14]. The skin is responsible for many functions including secretory, sensory, and defense [15]. It protects internal organs and tissues, receives signals from the environment, and prevents excessive water loss. In addition to its biological functions, it defines a person's physical appearance, affecting his or her well-being and quality of life [16]. Skin characteristics such as hydration, pH, and TEWL ensure the integrity of the epidermal barrier. TEWL, defined as the amount of condensed water diffusing through a fixed area of the stratum corneum into the air in a given unit of time, is one of the most important parameters characterizing the skin barrier. Increased values may be associated with epidermal barrier dysfunction [17]. In cryotherapy, the skin is directly exposed to low temperatures. A decrease in peripheral temperature, primarily of the skin, triggers basic thermoregulatory responses aimed at maintaining a constant body temperature. There is a constriction of blood vessels in the skin bed, reducing blood flow and consequently minimizing heat transfer between the body's core and outer layers [18; 19]. As previous studies have indicated, the effects of low-temperature treatments on the human body are dependent on body composition [8; 20]. These reactions are most likely related to the presence of adipose tissue acting as an insulator. On the other hand, however, it has also been pointed out that body composition has a strong influence on skin condition [21]. Individuals with a higher BMI have been reported to have higher traumatic scores, indicating reduced skin barrier capacity [22]. This may be related to the presence of chronic, subclinical inflammation that is part of obesity and metabolic syndrome. Its presence is associated with a higher incidence of certain dermatoses in obese individuals [23]. Single exposures to cold [13] and the use of a series of WBC treatments [24] and their effects on basic skin characteristics have already been the subject of scientific research. However, the number of publications addressing this topic is still small. A 2021 study [13] evaluated the effect of a single 3 min WBC treatment on skin features. A total of 77 young people (age 23.63 \(\pm\) 1.36) participated. This study suggests that a single WBC treatment leads to an improvement in skin hydration and a decrease in acid-base reaction, but statistical significance was not reached. However, an unfavorable direction of change was indicated for skin barrier function as assessed by evaluating TEWL (transepidermal water loss), measured in men on the zygomatic bone. The study by [PERSON] et al. [24] involved 22 middle-aged women (58.7 \(\pm\) 7.54) who underwent 10 WBC treatments. Skin characteristics were measured before and after the first and last treatment. After the first treatment, there was an increase in hydration, which was statistically significant in only one of the eight measured locations on the body. An adverse effect on the hydration level of the stratum corneum was noted for the entire treatment series.