Beppu Onsen

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.

Sodium chloride springs — essentially natural saltwater baths — are celebrated for their warming and moisturising effects. The salt forms a thin film on the skin after bathing that slows moisture evaporation, keeping skin hydrated longer than a freshwater bath. This "heat-retaining" property means bathers stay warm for significantly longer after leaving the water, making these springs especially popular in winter. Salt springs are among the most accessible for first-time onsen visitors.

Those with high blood pressure or heart conditions should consult a doctor before bathing, as the warming effect increases circulation. Avoid immersing open wounds. The salt will sting slightly in eyes — take care when submerging.

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.

Simple thermal springs (単純温泉) have a lower dissolved mineral content than other spring types but are valued for the pure therapeutic effect of heat immersion itself. The warmth increases core body temperature, promotes sweating, eases muscle tension, and improves peripheral circulation. Simple thermal springs are the most common onsen type in Japan and are recommended as the gentlest introduction to onsen bathing — suitable for a wide range of health conditions and ages.

Simple thermal springs are the most broadly accessible onsen type. Standard precautions apply: avoid bathing within 30 minutes of eating, keep soaks to 10–15 minutes for first-timers, and hydrate before and after.