## 1 Introduction  
Kefalonia Island, one of the larger islands in Greece and the largest in western Greece, belongs to the Ionian Islands. It is a famous vacation spot that hosts thousands of tourists every year. One activity that visitors enjoy on this island is the \"well-known\" mud bath, using local geomaterial with clay minerals in Xi Beach, located in the Lixouri area. More specifically, Kefalonia island became a member of the International parks of Unesco (geopark) in the last few years, receiving extended visibility from visitors looking for points of interest such as these pelotherapy spots. Clay minerals focused the interest of the researchers during the last decades due to their special characteristics. As they are natural materials with advanced properties and low cost, their exploitation increased, with the main aim being their use in industrial applications [1]. Greece contains clay minerals deposits and occurrences that were extensively investigated for their characteristics as well as their industrial applications, which differ from one mineral to another [2, 3, 4]. A variety of clay minerals are used in the cosmetics industry due to their several optimum physical, as well as physicochemical, properties, such as specific surface area, high adsorption capacity, swelling capacity and reactivity to acids [5, 6]. Clay minerals and their microstructural characteristics, as mentioned, are the subject of numerous studies in various fields, such as geology, cosmetiology, materials science, pharmacy and medicine. They were used as traditional folk remedies for more than 2000 years because of their health benefits. Nowadays, they are utilized in traditional healing therapies and other natural skin care products [7; 8; 9]. [PERSON] and [PERSON] [10] related the ultrastructure of the colloidal dispersions of clay to the rheological properties affecting peloid application. However, peloid microstructure was previously specifically and systematically studied by very few authors, such as [PERSON] et al. [11]. Numerous researchers studied the use of clays in the preparation of peloids and dermcosmetic products [5; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21], and they found that the main phyllosilicates presented are smectites, kaolinite, illite, illite-smectite mixed layers, and chlorite in different proportions [6]. A comparative physico-chemical composition study of muds from different areas in the Homogeneous Euganean Hills Hydromineral Basin (B.I.O.C.E. ), Italy, reported the composition of peloids as \"claysey-silt\" (65.42% silt and 24.62% clay) and \"silty-clay\" (64.37% clay and 34.41% silt). Their heavy metal content was studied via comparison with commercial cosmetic mud and was found to be higher than in commercial mud; however, no allergic reactions were detected. A proposal to establish a protocol for effective control of these types of natural products was proposed in [22]. The use of natural cosmetic products is increasing around the world. Despite their natural origin, the risks of intoxication, allergic processes, prolonged chemical exposure, or presence of other side effects are significant. Mud baths with peloids were traditionally used for cosmetic or therapeutic purposes. Peloids are wet or dry fine-grained geomaterials composed of clay minerals, such as smectite, muscovite and kaolinite, as well as non-clay minerals, i.e., quartz, calcite and feldspars, in several amounts and with or without organic matter [23]. Generally, peloids derived from bentonite that have chemical and rheological properties, such as appropriate heat dissipation and high swelling potential, as well as operability properties, may be considered as suitable for pelotherapy. However, pelotherapy results depend on a complex of various parameters, such as physical skin characteristics, the temperature of skin or peloid, duration of external application and light exposure, amount of coated peloid paste on skin, etc.