All about onsen

22 Aug 2019 in Just Relax

From bubbling pools to luxury resorts, discover the world of Japanese hot springs.


As a land of volcanic activity, Japan has plenty of hot springs. In total, there are estimated to be some 30,000 dotted around the country, with around 3,000 transformed into onsen resorts. These facilities offer traditional ryokan-style accommodation, allowing guests to make the most of the bathing experience.

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If you’re looking for a unique insight into Japanese culture – as well as total-body relaxation, a visit to an onsen is a must. But what kind of onsen should you choose? How should you behave in the public baths? And how can you get the most from your hot spring experience?

A long history

In Japan, the official definition of hot springs is any water, steam or gas that originates from underground at a temperature of at least 25C and contains different salts and minerals. Most hot springs are of volcanic origin, with the water heated by magma several kilometres deep into the Earth’s crust and jettisoned to the surface. In onsen facilities, the water temperature is usually around 40C.

Hot springs have long had an important role in Japanese society, closely associated with the ritualistic cleansing of body and soul since the rise of Buddhism in the 6th century.



And from the early 18th century, they were recognized by the medical community for their curative and restorative powers. Today, numerous hot spring hospitals still offer treatments for everything from rheumatism to post-operation recovery.


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Many towns have forged their reputation on the quality of their onsen. Hakone, home to Hoshino Resorts KAI Hakone, is known nationwide for its baths dating back to the 8th century.


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And in the foothills of the Japanese Alps, HOSHINOYA Karuizawa has a century-old history. It was established in 1914 by Kasuke Hoshino, and has since been transformed into a luxury onsen resort by the 4th generation of the family.


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Mineral benefits

The mineral content of hot springs can vary significantly depending on their source. And each type of hot spring is said to have different effects on the skin and body, with many Japanese people claiming to feel the difference as soon as they enter the water.



A so-called “simple” hot spring is one that contains only small amounts of minerals and has an alkaline pH of 8.5 or more. These hot springs, which include those at lakeside Hoshino Resorts KAI Nikko in the Nikko National Park, are known for reducing fatigue and gently stimulating the skin. The alkalinity also helps to soften collagen and remove sebum, an oily secretion that can cause acne.


Chloride hot springs, such as Hoshino Resorts KAI Hakone, are rich in chloride and sodium, with the salt coating the body and helping to warm and moisturize the skin. Sulfate baths, meanwhile, help hydrate the skin, protecting it from drying out and accelerating the body’s natural healing process.

At Hoshino Resorts KAI Ito on the Izu Peninsula, the sulfate baths are also rich in calcium, giving the skin a smooth, silky glow.


Private or public

Most onsen offer single-sex public bathing, where visitors must respect a certain etiquette. This involves washing your body and hair at the shower space before you enter the water, tying up long hair and covering any tattoos. And you need to be naked: swimming costumes are not allowed! To optimize the experience, many Japanese use special breathing and stretching exercises to draw minerals into the body and improve the circulation.

At Hoshino Resorts, the onsen feature both indoor and outdoor public baths, usually with a view of nature.



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At Hoshino Resorts KAI Hakone, you can bathe while contemplating the verdant hillsides of Mt. Yusaka. And at Hoshino Resorts Oirase Keiryu hotel, the outdoor baths overlook the spectacular Oirase Gorge.


For an original onsen experience, head to HOSHINOYA Karuizawa, where you can bathe in the dark, or to HOSHINOYA Tokyo, where the roof-top baths are open all through the night, allowing you to gaze up at the stars in the middle of Tokyo.

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And for the ultimate luxury, why not treat yourself to a room with your own private onsen? Many Hoshino Resorts properties offer this service, but perhaps the ultimate setting is at Hoshino Resorts KAI Aso, where each private villa features an expansive terrace with a large hot spring tub, illuminated by a flaming torch at night.



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What better way to loosen your muscles after a day walking in the volcanic wilderness of the surrounding Aso-Kuju National Park?

Now you’ve read the article, test your knowledge with our Onsen Quiz!

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