I know from everything that I read that Japan is a super clean country. I have never been at an onsen but I read about related customs and I know that people wash themselves before entering without bathing suits. I am wondering if there are any regulations for sanitizing the onsen, knowing that supposedly no chemicals are used and the water temperature is not hot enough for killing potentially harmful bacteria. I hope nobody gets offended and that someone knows the answer. Thanks.

The more private ones are like bathtubs-they’re cleaned daily. It’s not like the water is just sitting there. Not like pool hot tubs. Which frankly I worry about sometimes. And the more public ones are closed for cleaning, at least where I stayed, so I’m assuming they are actually cleaned.

I don’t know specific regulations, but I’d say don’t worry about it, because it is true it is a very clean country. There’ve been plenty incidents at US hotels where even with chemicals, I wouldn’t use the pool or hot tub. I didn’t have any similar issues in Japan with the onsens. I might be more worried if you went to a resort where most guests are foreign, but the Japanese guests seem very serious about cleanliness in the Onsen. And then no diaper babies are allowed, or swimsuits, or even private towels—when you think about it, that eliminates LOT of the pathogens you’d find at a public swimming pool.

as usual, though- it’s personal choice. If I was immunocompromised, I probably wouldn’t use public pools at all.

If you mean water quality before it reaches the onsen—they do test that.

Most onsen contain circulating water- either by pump or naturally, so the water isn't just sitting there. Watch how the other users scrub themselves, and follow suit. They scrub every inch of themselves!
It's also considered taboo to enter with any sores or when you are sick, so the odds are pretty good that you will be safer soaking in an onsen that you are eating at a breakfast buffet.
If you are still worried, go first thing in the morning when it has just been cleaned.

Soaking in an onsen followed by a massage is one of the great joys for me of traveling in Japan, feels like heaven.

Thanks for sharing your experiences. I will make a decision based on the place.

I think that would be wise. Onsen come in many "varieties"-- natural or man-made, enclosed or open, etc. I have no idea what the laws or regulations are, or the extent to which they are honored, but would think that you would do well to learn more about any specific onsen before committing to enjoy it.

Good luck!

Thanks kja.

I located some additional info I found on the topic for anyone who might be interested about the same at:

https://en.wikipedia.org/wiki/Onsen#Infections

Just curious -- did that report cause you to change your plans?

I don't know yet, kja. I will see.

Leaving some decisions to the last moment can be a very good strategy. Enjoy your trip, Suzanna!

Thanks, kja. I am sure I will have more questions for the experts between now and March, as I will be focusing on details.

Just a tip; the plural form of onsen is...onsen. Hard to trust a Wikipedia article that keeps mentioning onsens. Same with Sento.

Soaking in an onsen are some of my greatest memories of my two trips (thus far) to Japan. An outdoor onsen on a chilly November night while all of the other barbers around me spoke Japanese provided a realization of “wow, you are really HERE”. And on my final morning on my trip this past year, chatting at the rotenburo outside my ryokan with a Japanese gentleman while staring out at snow capped Mt. Fuji was just incredible. Don’t cheat yourself out of these experiences.

That wiki mentions " potential side effects to onsen usage, such as high blood pressure or heart disease", but it misuses the term "side effect". Onsen use won't cause those conditions, but if you have either or both conditions then onsen usage is potentially dangerous. Same for saunas and hot tubs.

There is one practice that I wish Japanese would stop: the quick soak before scrubbing clean. They douse their bodies with buckets of water from the bath and then get in for a short soak, I think to "loosen the dirt", before doing the soaping and scrubbing. After cleaning they go for a longer soak.

The rinse is ok, it is the pre-soak that can leave a layer of oil and scum on the water. I think I saw this only once, at a hotel in Kirishima Onsen. It had a small indoor bath and then a large rotenburo with mountain views. You could see all the way to Sakurajima. I went for an early soak then went to a lounge area outside the onsen entrance. Watched the sumo tournament on TV with some new friends and all the while there were people coming and going from the bath. It was a holday, so it was busy. When I went back in the onsen area later that small indoor bath, the first one at the entrance, was unattractive.

In every case, though, the water is continuously exchanged. Water is flowing in and out.

Have never seen that.

The most interesting was the Denkiburo, hope I've got it right, or an electric bath, more a small lap pool sized "killer' tub often in an insignificant corner of an onsen. Beware. More a stun gun water pond , electrifying and scary. Designed to zap the daylights out of you, said to cure many an ailment, so they say,from impotency to headaches.Hangovers to haemorhoids. It'll probably also reboot your pace maker if you have one.
While i crawled into a quiet corner of an onsen , reasonably naked,away from the local soaked crowd, slipped into one of these....shot out with a yelp, dived in to an adjoining pool,a triple summersault, with a whole bunch of locals in raptures.....the joke was on me.... I survived.

Yikes!

@ inquest: OMG! Yikes is right!!!

My very limited understanding is that onsen differ in the types and extent of various minerals, including radium. Risks would, I think, vary with the person and the onsen.

All of the ryokan that I have been to (we have been to over 20 so far all throughout Japan some multiple times) and hotels with baths will close their baths at certain times everyday to drain and clean the baths. In ryokan this time is usually between 11:00 am to 3:00 pm. The hotels cleaning times will vary, some do it in the overnight hours when the baths are closed. I have also been to more rustic baths along the roadsides like on Hokkaido where the baths are not cleaned and some that are only cleaned periodically but for the most part most all ryokan and hotels clean their baths daily as cleanliness is a real big thing in Japan. I would not stay in a ryokan or hotel that did'nt clean their baths daily. You can ask your ryokan when their bath cleaning schedules are if you want but as most people only stay overnight and miss the cleaning times they don't tell you at check in unless you stay 2 days or more. Enjoy a ryokan and the baths its the most Japanese thing that you will do while there and not to be missed imho

Aloha!