Dai-ichi Takimotokan

Sulfate springs (硫酸塩泉) contain dissolved calcium, sodium, or magnesium sulfate and are among the most therapeutically versatile spring types. Calcium sulfate springs are traditionally associated with wound healing and post-surgical recovery — the calcium ions support tissue repair and the sulfate has mild astringent properties. Sodium sulfate springs are linked to liver and digestive function; they are one of the few spring types used in Japan's national spa therapy clinics for chronic digestive complaints. The water typically has a clean, slightly bitter mineral taste.

Sulfate springs are generally well-tolerated. Those with kidney stones of the calcium oxalate type should consult a doctor before bathing regularly. Sodium sulfate springs can have a mild laxative effect in sensitive individuals — stay hydrated.

Sulfuric hot springs are among the most studied in Japanese balneology. The sulfur compounds — primarily hydrogen sulfide and thiosulfate — have documented antimicrobial and anti-inflammatory properties. Regular bathing is associated with relief from chronic skin conditions including eczema and psoriasis, as well as joint inflammation and muscle soreness. Sulfuric waters have been prescribed in Japanese medical practice since the Edo period.

The distinctive rotten-egg smell dissipates quickly after leaving the bath. Avoid if you have a sulfur allergy, very sensitive skin, or respiratory conditions. Remove silver jewellery before entering — sulfur will blacken it permanently.

Iron-bearing springs are recognised by their characteristic rust-red or amber colour and metallic taste. The iron content — primarily ferrous bicarbonate or ferric sulfate — is associated with stimulation of red blood cell production and is traditionally recommended for anaemia and fatigue recovery. The distinctive colouring comes from iron oxidising on contact with air and is not a sign of contamination.

Iron springs will stain light-coloured swimwear and towels a persistent brownish-orange. Avoid wearing white or light fabrics into the water. Those with haemochromatosis (iron overload condition) should seek medical advice before bathing.

Bicarbonate springs (sodium bicarbonate, calcium bicarbonate, or hydrogen carbonate) are particularly effective for skin conditions. The bicarbonate ions cleanse and soften the skin surface, removing excess sebum without stripping the skin's acid mantle. These springs are traditionally recommended for acne-prone skin and as a gentle option for sensitive skin types. The water has a characteristically clean, soft feel.

Bicarbonate springs are generally among the most gentle and well-tolerated onsen types. Those with very dry skin may wish to apply moisturiser after bathing, as the cleansing effect can temporarily reduce surface oils.