The present study pretends to show what distinguishes natural peloids from artificial peloids. The last peloids referred to although being based mainly on natural constituents too, since they undergo design, manipulation, refining, maturation and beneficiation in an artificial environment are hereafter called designed and engineered peloids. Natural peloids are being less and less used in Thermal spas or Health resorts of all countries where traditionally have been used, and the reasons for that will be herewith referred to. It will be shown that the designed and engineered peloids could advantageously replace the use of natural peloids in Thermal spas, the advantages being threefold: 1. Simple composition based on raw materials, such as the almost monomineralic commercial clays kaolin or bentonite of both therapeutic and cosmetic grades, and the natural mineral water from a particular Thermal spa also recognized by their medicinal properties; 2. Easy incorporation of pharmacologically and medically recognized functional active principles, natural or synthetic, and inorganic or organic, into the maturated paste prepared with kaolin/natural mineral water or bentonite/natural mineral water; 3. Simple and effective sanitary control. Therefore, the identification, the control and the assessment of the healing action particularly provided by both natural mineral water and functional active principles existing in a certain peloid would be much easier with the simple composition of a designed and engineered peloid than with the complex composition of a natural peloid.