Although swimsuits are allowed in a select few onsen, this is very rare. In most onsen, you take off all your clothes in the dressing room. Clothing and garments that are worn outside are considered sullied and should never be brought into an onsen. Nudity is a must for taking an onsen.
That being said, some Japanese onsen allow for bathing suits, but this is rare (and such an onsen will usually not provide the most authentic experience) and is typically found in more tourist-friendly hotels and resorts, if at all.
First, what do you wear in an onsen? With a few exceptions (like Kitahama TERMAS and Kaihin Sunayu) you will be completely nude while bathing and separated by gender, so there is no need to worry too much about your outfit. Perhaps easily removable clothing is preferable.
In general, it is acceptable for men to shave in the shower area of the onsen, and razors are even provided. For women, it is not generally acceptable to shave in the onsen as this is seen as an activity that should be done privately. Japan is still a bit behind the times in gender equality.
Amongst Muslims, hair removal is part of an impulse towards general purity and cleanliness and includes the trimming of nails and the removing of armpit and pubic hair. Both men and women should remove armpit and pubic hair at least every forty days.
The shortest answer to this, based on research on medical publications and articles in Japanese, doctors would in general not encourage you to go into an onsen while on your period. The most common reasons are that: It's unsanitary and disrespectful toward other people.
Avoid bathing in an onsen in the following cases. If you have chronic bronchitis and fever or difficulty in breathing. If you have stable angina and chest pain becomes frequent. Bathing may cause serious problems with dehydration or thrombosis.
The Japanese have perfected the art of onsen, or hot spring baths, for centuries. Traditionally, men and women would bathe together in the same facility, but these days the baths are segregated by gender. Today, konyoku (mixed-gender onsen) are hard to find, with places like Tokyo having bans on such establishments.
This is a snapshot of things to remember not to do in the onsen bath: Don't put your small towel or hair in the onsen bath water. Don't use your phone or camera in public onsen.
Onsen etiquette
Take a shower to cleanse yourself before bathing. Most onsens provide soap and shampoo for you to use. If not, you have to buy some. It's best not to eat before bathing in the onsen, but you need to drink a lot of water before and after your onsen bath.
It is recommended that you do not shower after bathing in an onsen, as rinsing your body will weaken the minerals' healing effects.
Duration of bathing depends on the temperatures of water, but generally it shall be around 3-10 minutes at one time, and can be extended to 15-20 minutes if you get used to it.
Massage with Onsen
It is essential that the hot springs are kept clean, so all guests need to shower thoroughly before entering. Since many massages involve oils, it is best to get your massage treatment later so that none of the massage oils will get in the onsen.
No matter the size of your tattoo, ink is no problem.
However, times are changing, and more and more onsen have relaxed their policies—in some cases to accommodate tattooed foreign tourists.
Each establishment has its own pricing system, but generally, you can expect private onsen costs to run between 1500 to 3000 yen per hour. However, at some special onsen in Beppu, the onsen can be as cheap as the price of a coffee, such as at Sabo Takasaki, or even free at secret onsen, such as Hebin Yu.
It's good manners to avoid using onsens during menstruation, particularly on heavy flow days, even when using a tampon. Onsens, like pools in Japan, do not use powerful disinfectants, so it's not very sanitary for anyone involved.
Although onsens are visited to keep healthy rejuvenate the body, there are also a few risks if you're not careful. Firstly, don't stay in the onsen for too long - generally speaking 30-40 minutes total is enough time to reap the benefits of the mineral rich water and not overdo it.
Some onsen have a strong sulfuric smell while others have a weaker one but, in general, the milkier the water, the stronger the sulfuric smell.
Onsen etiquette
It's best not to eat before bathing in the onsen, but you need to drink a lot of water before and after your onsen bath.
But there's one particular rule around bathing in an onsen that may forbid many tourists: people with tattoos are not allowed in.
Typically it is not permitted to take photos while inside an onsen, unless you are visiting a private onsen. Be sure to check out our Niseko and Hakuba onsen guides for a list of our top 10 in each area!
In the onsen you will rarely see anyone walking around in a towel, but if you want to keep covered up before you hop into the water, you can. You can rent a towel for a small fee, and most onsens will provide you with a 'modesty towel' to walk into the onsen with.
Wash Before Entering the Onsen, Don't Wash in the Onsen
It's customary, polite and hygienic to wash your hair and body before entering the onsen water. This keeps it clean for everyone. Nobody wants to sit in someone else's dirty bathwater.
Now, drinking milk after visiting sento, taking a bath, or getting out of onsen is almost as if written into the Japanese DNA. Milk and bathing are as inseparable as beer and edamame or wine and cheese. So next time you are wondering what you should do after onsen, consider drinking a cold glass of milk.