An onsen (温泉) is a term for hot springs in the Japanese language, though the term is often used to describe the bathing facilities and inns around the hot springs. As a volcanically active country, Japan has thousands of onsen scattered along its length and breadth. Onsen were traditionally used as public bathing places and today play a central role in directing Japanese domestic tourism.
Onsen come in many types and shapes, including outdoor (露天風呂 or 野天風呂 roten-buro or noten-buro ) and indoor baths. Baths may be either public run by a municipality or private (内湯 uchiyu ) often run as part of a hotel, ryokan or bed and breakfast (民宿 minshuku ).
Onsen are a central feature of Japanese tourism often found out in the countryside but there are a number of popular establishments still found within major cities. They are a major tourist attraction drawing Japanese couples, families or company groups who want to get away from the hectic life of the city to relax. Japanese often talk of the virtues of "naked communion" (裸の付き合い hadaka no tsukiai ) for breaking down barriers and getting to know people in the relaxed homey atmosphere of a ryokan with an attached onsen. Japanese television channels often feature special programs about local onsens.
The presence of an onsen is often indicated on signs and maps by the symbol ♨ or the kanji, 湯 (yu, meaning "hot water"). Sometimes the simpler hiragana character ゆ (yu) is used, to be understandable to younger children.
Traditionally, onsen were located outdoors, although a large number of inns have now built indoor bathing facilities as well. Onsen by definition use naturally hot water from geothermally heated springs. Onsen should be differentiated from sentō, indoor public bath houses where the baths are filled with heated tap water. The legal definition of an onsen includes that its water must contain at least one of 19 designated chemical elements, including radon and metabolic acid and be 25 °C or warmer before being reheated. Stratifications exist for waters of different temperatures. Major onsen resort hotels often feature a wide variety of themed spa baths and artificial waterfalls in the bathing area utaseyu (打たせ湯).
Onsen water is believed to have healing powers derived from its mineral content. A particular onsen may feature several different baths, each with water with a different mineral composition. The outdoor bath tubs are most often made from Japanese cypress, marble or granite, while indoor tubs may be made with tile, acrylic glass or stainless steel. Different onsen also boast about their different waters or mineral compositions, plus what healing properties these may contain. Other services like massages may be offered.
Traditionally, men and women bathed together at the onsen and sentō but single-sex bathing has become legalized as the norm since the opening of Japan to the West during the Meiji period. Mixed bathing (混浴 kon'yoku ) persists at some special onsen in the rural areas of Japan, which usually also provide the option of separate "women-only" baths or different hours for the two sexes. Children of either sex may be seen in both the men's and the women's baths.
People often travel to onsen with work colleagues, friends, couples or their families.
Ensuring cleanliness 
At an onsen, as at a sentō, all guests are expected to wash their bodies 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.
Bathers are not normally allowed to wear swimsuits in the baths. However, some modern onsen with more of a waterpark atmosphere require their guests to wear a swimming suit in their mixed baths.
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 sometimes against the rules to immerse or dip towels in the onsen bath water, since this can be considered unclean. In this latter case, 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.
Onsen vary from quiet to noisy, some play piped music and often feature gushing fountains. Bathers will engage in conversation in this relaxed situation. There are usually prohibitions against rowdiness in the washing and bathing areas. A small amount of excess energy and splashing around is usually tolerated from children, however.
Many onsen ban bathers with tattoos, which in Japan, as in the West prior to the radical changes that have taken place in society, are perceived as a badge of criminality—Yakuza traditionally have elaborate tattoos. Despite this background reason, the rule is often enforced strictly against all, including foreigners, women, and even when tattoos are small and "peaceful".
The volcanic nature of Japan provides plenty of springs. When the onsen's water contains distinctive minerals or chemicals, the onsen establishments display what type of onsen it is.
Some examples of types of onsen include:
- Sulphur 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 )
- Iron onsen (鉄泉 tetsu-sen )
In Japan, it is said onsen have various medical effects. Japanese people believe that a good soak in proper onsen heals aches, pains and diseases, and visit onsen to treat the illnesses, such as arthralgia, chronic skin diseases, diabetes, constipation, menstrual disorders and so on.
These medical benefits have given onsen a central role in balneotherapy which is called "Onsen Therapy" (温泉療法 onsen-ryōhō ). Onsen Therapy is a comprehensive bathing treatment conducted to maintain health, normalize dysfunctions and prevent illness.
Although millions of Japanese bathe in onsen every year with few noticeable side effects, there are still contraindications to onsen usage, such as high blood pressure or heart disease.
In recent years, Legionella bacteria have been found sporadically in onsen with poor sanitation. Revelations of poor sanitary practices at some onsen have led to improved regulation by hot spring communities to maintain their reputation.
There have been reports of infectious disease found in hot bodies of water worldwide, such as:
- Various Naegleria species. While studies have found the presence of Naegleria in hot spring waters, the worrisome Naegleria fowleri amoeba has not been identified. Nevertheless, less than 5 cases have been seen historically in Japan, although not conclusively linked to onsen exposure.
Many onsen have posted notices for visitors, reminding anyone with open cuts, sores, or lesions to not 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 instead does not recycle its water, cleaning baths daily. These precautions as well as proper onsen usage (i.e. not placing the head underwater, washing thoroughly before entering the bath) greatly reduces any overall risk to bathers.
In 2001, onsen owners in the port city of Otaru, Hokkaido referred to incidents of rowdy Russian fishermen bothering other customers and causing lost business as reason to refuse service to anyone not Japanese. This issue was highlighted in February 2001, when naturalized-Japanese Debito Arudou and two co-plaintiffs sued Yunohana Onsen in Otaru, Hokkaidō, for openly refusing service to customers because of their race. Yunohana Onsen lost the lawsuit in November 2002.
In another case of discrimination, Kurokawa Onsen Hotel in Kumamoto Prefecture ran into legal trouble when leprosy patients were refused entry. Leprosy is not contagious once treated, and laws that used to force seclusion on leprosy patients have long been overturned.
Out of the thousands of onsen in operation in Japan, there have been few reports of businesses practicing discrimination of this kind.
Selected onsen 
- Akagi, Gunma
- Akayu, Yamagata
- Arima Onsen, Kobe, Hyōgo
- Asamushi Onsen, Aomori Prefecture
- Aso, Kumamoto, a famous onsen area alongside Mount Aso, an active volcano
- Atami Onsen (ja), Atami, Shizuoka, major onsen resort town near Tokyo
- Template:Awara Onsen, Awara, Fukui Prefecture
- Awazu Onsen (ja), Komatsu, Ishikawa
- Beppu Onsen, Beppu, Ōita Prefecture, famous for its multi-coloured baths
- Dōgo Onsen, Ehime Prefecture
- Futamata, Hokkaidō
- Gero Onsen (ja), Gero, Gifu, famous for its free open bath on riverbank of Hida River
- Getō Onsen (ja), Iwate Prefecture
- Ginzan Onsen, Obanazawa, Yamagata
- Hakone, Kanagawa, famous onsen resort town near Tokyo
- Hanamaki, Iwate
- Hirayu Onsen (ja), Takayama, Gifu
- Hokkawa Onsen (ja), Shizuoka
- Ibusuki Onsen, Kagoshima Prefecture
- Ikaho Onsen (ja), Ikaho, Gunma
- Itō, Shizuoka
- Iwamuro, Niigata, famous for onsen since the Edo period
- Jigokudani, Nagano Prefecture
- Jōzankei Onsen (ja), Hokkaido
- Kaike Onsen (ja), Yonago, Tottori
- Kakeyu Onsen (ja), Nagano
- Kanzanji Onsen (ja), Shizuoka
- Katayamazu Onsen (ja), Kaga, Ishikawa
- Kawayu Onsen (ja), Tanabe, Wakayama
- Kindaichi Onsen, Iwate
- Kinosaki, Hyōgo
- Kinugawa Onsen, Tochigi
- Kurokawa Onsen, Aso, Kumamoto Prefecture
- Kusatsu Onsen, Gunma Prefecture
- Misasa Onsen (ja), Misasa, Tottori Prefecture
- Nagaragawa Onsen, Gifu, Gifu
- Sawatari, Gunma Prefecture
- Shima, Gunma Prefecture
- Nanki-Katsuura Onsen (ja), Nachikatsuura, Wakayama
- Nanki-Shirahama Onsen (ja), Shirahama, Wakayama Prefecture
- Naruko, Miyagi
- Noboribetsu, Hokkaido
- Nuruyu Onsen, Kumamoto Prefecture
- Nyūtō Onsen (ja), Akita Prefecture
- Onneyu Onsen (ja), Hokkaido
- Ōfuka Onsen, Akita
- Ryujin Onsen (ja), Tanabe, Wakayama, one of Japan's famous three beautifying onsen
- Sabakoyu Onsen, Fukushima Prefecture, the oldest community onsen in Japan
- Sakunami Onsen, Miyagi
- Senami Onsen (ja), Niigata Prefecture
- Shimabara, Nagasaki
- Shimobe Onsen (ja), Yamanashi Prefecture
- Shiobara Onsen (ja), Tochigi Prefecture
- Shuzenji Onsen (ja), Shizuoka Prefecture
- Sōunkyo Onsen (ja), Hokkaido
- Sukayu Onsen, Aomori Prefecture
- Sumatakyō Onsen (ja), Shizuoka Prefecture
- Suwa, Nagano Prefecture
- Takanoyu Onsen, Akita Prefecture
- Takaragawa, Gunma, one of the largest outdoor mixed baths in Japan
- Takarazuka, Hyōgo
- Tara, Saga
- Tōyako, Hokkaidō
- Tsubame Onsen (ja), Niigata - famous for its free open mixed onsen
- Tsukioka Onsen, Niigata (ja), Niigata Prefecture
- Tsurumaki Onsen (ja), Kanagawa
- Unazuki Onsen (ja), Kurobe, Toyama Prefecture
- Wakura Onsen, Nanao, Ishikawa Prefecture
- Yamanaka Onsen, Kaga, Ishikawa
- Yamashiro Onsen (ja), Kaga, Ishikawa
- Yubara Onsen (ja), Okayama Prefecture, one of the largest mixed baths at the foot of Yubara dam
- Yudanaka Onsen (ja), Nagano Prefecture
- Yufuin, Ōita Prefecture
- Yugawara, Kanagawa Prefecture
- Yumura Onsen (ja), (Shin'onsen, Hyōgo)
- Yunogo Onsen, Okayama Prefecture
- Yunokawa Onsen, Hokkaido
- Yunomine Onsen (ja), Tanabe, Wakayama, site of the UNESCO World Heritage Tsuboyu bath
- Yuzawa, Niigata
- Zaō Onsen, Yamagata Prefecture
See also 
- This term should be carefully differentiated from the word skinship (スキンシップ sukinshippu ) which refers to the benefits of physical contact, for instance, on babies by their mothers.
- In very isolated onsen, where there is no possibility to use soap before entering in the bath, onsen users are expected to at least rinse their body with the water of the bath before entering it.
- Covering the offending tattoo with sticking plaster can sometimes solve the problem. "Onsen Warnings and Hassles"
- Tattoo in Japan (2009-12-22). "Tattoo in Japan". Boing Boing. Retrieved 2010-12-07.
- "Sunnypages - Tokyo reviews by English speakers". Sunnypages.jp. Retrieved 2010-12-07.
- Getting into hot water for health. The Japan Times. May 25, 2003.
- "Hot Spring Treatment｜Hot Spring Encyclopedia｜ONSEN｜BEPPU CITY｜". City.beppu.oita.jp. Retrieved 2010-12-07.
- H. Miyamoto; S. Jitsurong, R. Shiota, K. Maruta, S. Yoshida, E. Yabuuchi (1997). "Molecular determination of infection source of a sporadic Legionella pneumonia case associated with a hot spring bath". Microbiol Immunol. 41 (3): 197–202. PMID 9130230.
- Eiko Yabuuchi; Kunio Agata, Kansenshogaku zasshi (Kansenshogaku zasshi) (2004). "An outbreak of legionellosis in a new facility of hot spring Bath in Hiuga City". Kansenshogaku zasshi 78 (2): 90–98. ISBN 0387-5911 Check
|isbn=value (help). PMID 15103899.
- "Onsen: know what you're getting into". The Japan Times.
- Shinji Izumiyama; Kenji Yagita, Reiko Furushima-Shimogawara, Tokiko Asakura, Tatsuya Karasudani, Takuro Endō (07 2003). "Occurrence and Distribution of Naegleria Species in Thermal Waters in Japan". The Journal of Eukaryotic Microbiology 50 (s1): 514–5. doi:10.1111/j.1550-7408.2003.tb00614.x. PMID 14736147.
- Yasuo Sugita; Teruhiko Fujii, Itsurou Hayashi, Takachika Aoki, Toshirō Yokoyama, Minoru Morimatsu, Toshihide Fukuma & Yoshiaki Takamiya (05 1999). "Primary amebic meningoencephalitis due to Naegleria fowleri: An autopsy case in Japan". Pathology International 49 (5): 468–70. doi:10.1046/j.1440-1827.1999.00893.x. PMID 10417693.
- Charles Scanlon (2001-02-01). "Bath house in hot water". BBC News. Retrieved 2003-11-21.
- Michael Hoffman (2002-04-21). "Quiet after Otaru onsen storm - Hokkaido public forum finds birthplace no bar to a bath". Japan Times.
- "Racist Japanese bathhouse fined". BBC News. 2002-11-11.
- "Japan lepers reject spa apology". BBC News. 2003-11-21.
Further reading 
- Hotta, Anne, and Yoko Ishiguro. A Guide to Japanese Hot Springs. New York: Kodansha America, 1986. ISBN 0-87011-720-3.
- Fujinami, Kōichi. Hot Springs in Japan. Tokyo: Board of Tourist Industry, Japanese Government Railways; Maruzen Company, Ltd., 1936.
- Neff, Robert. Japan's Hidden Hot Springs. Rutland, Vermont: Charles E. Tuttle, 1995. ISBN 0-8048-1949-1.
- Seki, Akihiko, and Elizabeth Heilman Brooke. The Japanese Spa: A Guide to Japan's Finest Ryokan and Onsen. Boston: Tuttle Publishing, 2005. ISBN 0-8048-3671-X. Reprinted as Ryokan: Japan's Finest Spas and Inns, 2007. ISBN 0-8048-3839-9.
|Wikimedia Commons has media related to: Hot springs of Japan|
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- Onsen of Fukuoka Prefecture from official page of Fukuoka Prefecture Tourism Association
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- Tanabe City Kumano Tourism Bureau Indepth information on onsen in Wakayama Prefecture