bath salts; bathwater additive; medicinal bath mix
A powdered or granular product added to bathwater to mimic hot spring water, often containing minerals, fragrances, and coloring.
When you add bath salts, the bath becomes like a hot spring.
I bought bath salts as a souvenir from my trip.
入浴剤 is a broader term for any bath additive (including oils, bubbles, etc.), while 温泉の素 specifically refers to products that recreate hot spring water.
Standard kanji spelling for this product name.
Alternate kanji spelling using 元; less common but still seen.
Compound of 温泉 (hot spring) + の (possessive particle) + 素 (element, ingredient). Literally 'hot spring ingredient', referring to a product that turns regular bathwater into a hot spring-like experience.