Onsen safety — seven rules against overheating, dizziness and scalding-hot baths
Most onsen accidents happen from staying in too long and from standing up too fast. Ten minutes per soak and a pause before you stand prevent most of them.
1. A glass of water before you go in
One soak costs 300–500 ml of sweat. Use the changing-room water dispenser or a bottle before and after. Bathing right after alcohol sends blood pressure swinging and is one of the most common causes of onsen accidents in Japan.
2. Ten minutes per soak, three soaks a day
At 42°C ten minutes warms you through. Short and repeated is easier on the body than one long soak. Sweat on your forehead means time to get out. Keep it to about three baths a day and avoid one right before bed.
3. Entering very hot water (43°C+)
- Pour water over yourself 10+ times: feet, then hips, then shoulders
- Slide in slowly and stay still (moving makes it feel hotter)
- Out after one or two minutes. Beginners: half-body or feet only
- Communal baths in Kusatsu, Nozawa and Beppu run 44–46°C as standard
4. Standing up is the most dangerous moment
Blood pressure drops in the water and can't catch up when you rise, causing a head rush. Sit on the rim for ten seconds, hold the rail and stand slowly. Wet floors and open-air rocks are slippery — watch your feet.
5. 'Nobose' versus 'yuatari'
| Nobose (overheating) | Yuatari (onsen sickness) | |
|---|---|---|
| When | During or right after | Hours later to next day |
| Signs | Flushed face, dizziness, racing heart | Fatigue, headache, nausea, no appetite |
| What to do | Get out, lie down somewhere cool, drink | Skip bathing for a day; fluids and rest |
Strong acidic (Kusatsu, Zao) and sulfur springs cause yuatari more easily. On multi-night stays, go easy on day one.
6. When not to bathe
- With a fever, right after alcohol, a big meal or hard exercise
- Early and late pregnancy: check with your doctor (no longer a legal contraindication in Japan, but fall and overheating risks remain)
- High blood pressure or heart conditions: 41°C or lower, under five minutes, half-body
- Under-threes: no long soaks — a few minutes in 38–40°C water
7. Sauna and cold-plunge order
Hot bath → cold plunge → rest outside. Jumping from the sauna straight into a hot spring doubles the load on your heart. Enter the cold bath gradually, feet to chest.