First: an onsen is not a sento

The difference is legal, not aesthetic. An onsen must use water from a natural geothermal source, at a defined temperature and mineral content - it's written into law. A sento is a public bathhouse using ordinary heated water.

The etiquette is identical, but a sento is everyday neighbourhood life (400 - 550 yen) while an onsen is a destination. At the entrance to an onsen there's always a board with the water analysis: composition, temperature, what it helps with.

The whole routine, in order

  1. Shoes go in a locker at the entrance, before the till.
  2. You pay, get a key and usually two towels: the big one stays in the changing room, the small one comes with you.
  3. The changing room is split into women's (red curtain, 女) and men's (blue, 男). You undress completely, everything goes into a basket or locker.
  4. Washing. You sit on a stool at a shower station and wash your whole body. Soap and shampoo are usually provided. Rinse thoroughly - you enter the water clean.
  5. The bath. Get in slowly and put the small towel on your head or on the edge. The towel never goes in the water.
  6. Getting out. Dry off with the small towel by the bath, so you don't drip through the changing room.

Rinse afterwards or not?

By default no - the minerals are meant to stay on your skin and keep working. The exception: strongly acidic or sulphurous springs can irritate, especially sensitive skin. In Kusatsu the water has a pH below 2, roughly lemon juice. Rinse with fresh water there.

Simple rule: if the water stings or smells strongly of sulphur, rinse. If it's mild, leave it.

Tattoos - no sugar-coating

Plenty of places still refuse entry with visible tattoos. The reason is historical and tied to yakuza associations, but in practice it's simply house rules. What you can do:

  • Small tattoo - cover it with a plaster. Chemists sell skin-toned patches made for this (tattoo seal).
  • Large one - look for places advertised as tattoo friendly. There are whole listings of them, and Beppu or Hakone have plenty.
  • Safest - book kashikiri, a private bath for 45 - 60 minutes. Usually 2,000 - 4,000 yen and nobody asks anything. Many ryokan include it.
  • A ryokan room with its own open-air bath (kashitsuki rotenburo) removes the problem entirely.

The things that genuinely matter

  • Tie long hair up so it doesn't touch the water.
  • No phones. This isn't about manners, it's house rules - people are naked in the changing room and photos are banned.
  • No swimming, diving or noise. An onsen is not a pool.
  • Don't get in after drinking. Hot water plus alcohol is a genuine fainting risk, not an exaggeration.
  • Drink water before and after. A quarter of an hour at 42 degrees dehydrates more than you'd think. There's almost always a vending machine at the exit.
  • Open wounds, dressings, fever - skip it. Same for heart conditions and high blood pressure without medical advice.

Types worth seeking out

  • Rotenburo - an open-air bath. In winter, in the snow, in Hokkaido or Kyushu - this is the experience people travel for.
  • Ashiyu - a free foot bath, often right by the station in a spa town. Great when you haven't time for a full bath.
  • Sand bath in Ibusuki, Kyushu - they bury you in hot sand by the sea. Strange and excellent.
  • Konyoku, mixed gender - rare these days, mostly at mountain inns.

Where to go

Classics close to the usual routes: Hakone (an hour from Tokyo), Kinosaki (a town you walk around in a yukata between seven bathhouses), Kusatsu (the strongest water in the country), Beppu and Yufuin in Kyushu, Noboribetsu in Hokkaido.

💡 From me: if you're going to feel self-conscious, book a private bath for the first time or go early in the morning when it's empty. After ten minutes it stops being an issue, genuinely. Nobody is looking at anybody.