Clays in pelotherapy. A review. Part II: Organic compounds, microbiology and medical applications

Abstract A review of the research on peloids and pelotherapy has been carried out considering only the publications in English. More than 300 publications were reviewed that included: articles, books and chapters from books related to the subject. Of them, a total of 198 have been chosen to be cited in the two papers related with this review (Part I and Part II), and 140 published in the period between 1990 and 2019 have been considered in this paper. In the present study a review on the organic compounds, organic matter content and microorganisms present in the peloids, as well as their therapeutic activity, were surveyed and analysed. The mineralogy, chemistry and physical and physicochemical properties of peloids, as well as historical background, definition and classification, forms of application, maturation process, presence of radioactive isotopes, peloid interstitial liquid, cation release and toxicity, are reviewed in the paper: Clays in pelotherapy. A review. Part I: Mineralogy, chemistry, physical and physicochemical properties (Carretero, 2020). The main microorganisms detected in peloids used with therapeutical purposes were microalgae, diatoms and thermophilic blue-green algae (Cyanobacteria) that are part of the so-called “bioglea”, which develop in some hot spring peloids and with a certain composition of minero-medicinal water and solid phase. Organic compounds were detected in the peloids that were associated to these microorganisms such as sulfoglycolipids, glycoglycerolipids, diacylglycerolipids, etc., which have proven anti-inflammatory properties. Many authors also indicated an antimicrobial action including the inhibitory effect on potential skin pathogens, that might partially explain the therapeutic properties of the peloids when they are used for dermatological diseases. Experimental findings or results of the therapeutic efficacy of peloids by means of in vitro and in vivo studies, or clinical trials or studies, demonstrated that the peloids improve the ailments of some diseases. Nevertheless the peloids are usually applied in combination with other techniques, therefore its therapeutic efficacy has not been fully demonstrated. On the other hand, there are numerous researches conducted on the study of clays for their possible use as peloids, which include the study of the mineralogical, chemical composition and physical and physicochemical properties of the obtained peloids. They are described in the part I of the review of clays in pelotherapy (Carretero, 2020). It should be said that the peloids used in the studies for their therapeutic efficacy are not characterized from the point of view of their mineralogical, chemical, physical, and physicochemical properties. There are also few studies carried out on the organic compounds and microorganisms present in peloids, and their relationship with their therapeutic activity. It should be noted that in no case was the composition and properties of the peloids related to their therapeutic efficacy. Therefore, these lines of research should be considered in the coming years.