Onsen (温泉) is a Japanese word that translates in English as hot spa. Onsen is a specific type of hot spa, that is a naturally occurring hot spa caused from thousands of years of underground volcanic eruptions. Hot springs are heated naturally from underground magma, known as a geothermal reaction. There are however Onsen’s that are heated from unnatural sources, and according to Japanese law they must be heated to more than 25°C to be classified as an Onsen.Hot springs are traditionally believed to have healing qualities, and there are Onsen’s that are advertised for specific needs based on its mineral composition. People may go to an Onsen to try to ease symptoms of muscle pain, arthritis, arthralgia, chronic skin diseases, or diabetes. An Onsen must have at least one of nineteen specific mineral or chemical elements, it is the naturally occurring minerals that are believed to have the healing effects on the body.
An Onsen is indicated on signage and maps by the kanji symbol yu (湯) meaning hot water. Sometimes the Hiragana symbol is used (ゆ) as it is easier for younger people and foreigners to understand.
Bathers are not allowed to wear swimsuits in an Onsen and should bathe naked. There are some modernised Onsen that do allow people to wear a towel or swimsuit, but this is an exception. Before going to an Onsen you should try to become accustomed to the idea of bathing in a public area without clothes on. Towels can be used for modesty when walking between wash stations and bathing facilities, however they are not to be used in the water as it is considered unclean and that it can contaminate the water.
Other important factors to remember when visiting an Onsen is to tie up long hair so it does not fall into the water and do not put your head or face in the water, you must not be intoxicated or drink alcohol while bathing, maintain hygiene and cleanliness at all times, respect other people and keep noise to a minimum, be careful when entering the water as it will be hot it is advisable to enter slowly. Also after bathing it is possible the body will become dehydrated from the long bathing in water of such a high temperature, therefore drinking fluids is important after bathing in an Onsen.