expression, noun
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.
温泉の素を入れると、お風呂が温泉みたいになる。
When you add bath salts, the bath becomes like a hot spring.
旅行のお土産に温泉の素を買った。
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.
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.