Piešťany's healing sulfur mud contains various forms of sulfur and sulfur compounds (the main active ingredient), minerals such as calcium, magnesium, bromine, organic substances, and special thermotolerant sulfur bacterial flora It is one of the most unique and recognized natural peloids (medicinal substances) in the world. It is a key therapeutic resource at the Piešťany Spa and is used primarily for the treatment of musculoskeletal disorders.

On Spa Island, mineral water springs from 11 sources through cracks in tectonic plates at a depth of 60 to 200 meters below ground. The water reaches a very high temperature of 67–69 °C on the surface, so it is cooled before being used in the baths. The thermal mineral water is unique for its high content of sulfur (6–10 mg/l) and hydrogen sulfide (4,7 mg/l), which have beneficial effects in the treatment of chronic inflammation and diseases of the musculoskeletal system.