A video showcasing the stool and shower used for cleaning off, an inside pool and an outside pool

In Japan, onsen (温泉) are hot springs and the bathing facilities and traditional inns around them. There are approximately 25,000 hot spring sources throughout Japan, and approximately 3,000 onsen establishments use naturally hot water from these geothermally heated springs.^[1]

Onsen may be either outdoor baths (露天風呂 or 野天風呂, roten-buro / noten-buro) or indoor baths (内湯, uchiyu). Traditionally, onsen were located outdoors, although many inns have now built indoor bathing facilities as well. Nowadays, as most households have their own baths, the number of traditional public baths has decreased,^[2] but the popularity of sightseeing hot spring towns has increased.^[3]^{[better source needed]} Baths may be either publicly run by a municipality or privately, often connecting to a lodging establishment such as a hotel, ryokan, or minshuku.

The presence of an onsen is often indicated on signs and maps by the symbol ♨, the kanji 湯 (yu, meaning "hot water"), or the simpler phonetic hiragana character ゆ (yu).

Definition

According to the Japanese Hot Springs Act (温泉法, Onsen Hō), onsen is defined as "hot water, mineral water, and water vapor or other gas (excluding natural gas of which the principal component is hydrocarbon) gushing from underground".^[4] The law states that mineralized hot spring water that feeds an onsen must be at least 24 °C (75 °F) originating at a depth of at least 1.5 kilometres (0.93 mi), and contain specified amounts of minerals such as sulphur, sodium, iron, or magnesium.^[1]

When onsen water contains distinctive minerals or chemicals, establishments often display what type of water it is,^[5] in part because the specific minerals found in the water have been thought to provide health benefits.^[6] Types include sulfur onsen (硫黄泉, iō-sen), sodium chloride onsen (ナトリウム泉, natoriumu-sen), hydrogen carbonate onsen (炭酸泉, tansan-sen), and iron onsen (鉄泉, tetsu-sen).

Mixed bathing

Traditionally, men and women bathed together at both onsen and sentō communal bathhouses, but gender separation has been enforced at most institutions since the opening of Japan to the West during the Meiji Restoration. Mixed bathing (混浴, kon'yoku) persists at some onsen in rural areas of Japan,^[7] which usually also provide the option of separate "women-only" baths or different hours for the two sexes. Children are usually not limited by these rules.^{[citation needed]}

In some prefectures of Japan, including Tokyo, where nude mixed bathing is banned, people in mixed baths are required to wear swimsuits or yugi (湯着), which are specifically designed for bathing.^[8]

Etiquette

Ensuring cleanliness

As at a sentō at an onsen, all guests are expected to wash and rinse themselves thoroughly before entering the hot water. Bathing stations are equipped with stools, faucets, wooden buckets, and toiletries such as soap and shampoo; nearly all onsen also provide removable shower heads for bathing convenience. Entering the onsen while still dirty or with traces of soap on the body is socially unacceptable.^[a]

Swimsuits

Guests are not normally allowed to wear swimsuits in the baths. However, some modern onsen will require their guests to wear a swimming suit in their mixed baths.^[8]

Towel

Onsen guests generally bring a small towel with them to use as a wash cloth. The towel can also provide a modicum of modesty when walking between the washing area and the baths. Some onsen allow one to wear the towel into the baths, while others have posted signs prohibiting this, saying that it makes it harder to clean the bath. It is against the rules to immerse or dip towels in the onsen bath water, since this can be considered unclean. People normally set their towels off to the side of the water when enjoying the baths, or place their folded towels on top of their heads.

Tattoos

By 2015, around half (56%) of onsen operators had banned bathers with tattoos from using their facilities.^[9]^[10]^[11] The original reason for the tattoo ban was to keep out yakuza and members of other crime gangs who traditionally have elaborate full-body decoration.^[12]

However, tattoo-friendly onsen do exist.^[13] A 2015 study by the Japan National Tourism Organisation found that more than 30% of onsen operators at hotels and inns across the country will not turn someone with a tattoo away; another 13% said they would grant access to a tattooed guest under certain conditions, such as having the tattoo covered up.^[9] Some towns have many tattoo-friendly onsen that do not require guests to cover them up. Two such towns are Kinosaki Onsen in Hyōgo and Beppu Onsen in Ōita.^[14]

With the increase in foreign customers due to growing tourism, some onsen that previously banned tattoos are loosening their rules to allow guests with small tattoos to enter, provided they cover their tattoos with a patch or sticking plaster.^[9]^[15]

Risks

Article 18, paragraph 1 of the Japanese Hot Springs Act publishes guidance on contraindications and cautions for bathing in hot springs, and drinking their respective waters.^[16] Although millions of Japanese bathe in onsen every year with few noticeable side effects, there are still potential side effects to onsen usage, such as aggravating high blood pressure or heart disease.^[17]

Legionella bacteria have been found in some onsen with poor sanitation.^[18]^[19] For example, 295 people were infected with Legionella and seven died at an onsen in Miyazaki Prefecture in 2002.^[19]^[20]^[b] Revelations of poor sanitary practices at some onsen have led to improved regulation by hot-spring communities to maintain their reputation.^[21]

There have been reports of infectious disease found in hot bodies of water worldwide, such as various Naegleria species.^[22] While studies have found the presence of Naegleria in hot spring waters, Naegleria fowleri, responsible for numerous fatal cases of primary amoebic meningoencephalitis around the world, has not been found to be present in the water at onsen.^[22] Nevertheless, fewer than five cases have been seen historically in Japan, although not conclusively linked to onsen exposure.^[23]

Many onsen display notices reminding anyone with open cuts, sores, or lesions not to bathe. Additionally, in recent years onsen are increasingly adding chlorine to their waters to prevent infection, although many onsen purists seek natural, unchlorinated onsen that do not recycle their water but instead clean the baths daily.^[21] These precautions as well as proper onsen usage (i.e. not placing the head underwater, washing thoroughly before entering the bath) greatly reduce any overall risk to bathers.

Voyeurism is reported at some onsen.^[24]^[25] This is mitigated in some prefectures of Japan where nude mixed bathing is not permitted, visitors must wear swimsuits.^[8]

Selected onsen

Main article: List of hot springs in Japan

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