The signature smell of hot springs. Sulfur (as hydrogen sulfide and sulfates) is the mineral most traditionally associated with skin conditions.
Sulfur is the mineral that announces a hot spring before you see it — the "rotten-egg" aroma comes from hydrogen sulfide gas rising off the water. It has the longest history in balneotherapy of any mineral: sulfurous springs have been prescribed for skin and joint complaints for two thousand years. Studies suggest sulfur baths may help inflammatory skin conditions such as eczema, psoriasis, and acne, thanks to mild antibacterial and keratolytic (skin-softening) effects. The smell fades from your awareness within a few minutes of soaking.
How you'll know it
The unmistakable "rotten-egg" smell, often milky or pale-green water.
Traditionally good for
Associations from long use and emerging research — restorative, not medical claims.
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Traditionally used for eczema, psoriasis, and acne
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Mild antibacterial and antifungal properties
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Often reported to leave skin softer after soaking
Good to know
The smell is harmless, but soak in well-ventilated spots and rinse afterward. Sulfur can tarnish silver jewellery — take it off.
Springs rich in sulfur
Sources & further reading
For general interest, not medical advice. Benefit claims reflect long tradition and emerging research; the strength of evidence varies by mineral and condition.