What Is Onsen? A T+L Wellness Primer

Ready to take a dip? Here’s everything you need to know about Japanese onsen in order to experience it like a pro

What is onsen : Public hot spring, KAIKirishima

Public Hot Spring, KAIKirishima. Courtesy of Hoshino Resorts

By Kissa Castañeda

Feb 14, 2022


IT’S HARD TO IMAGINE A TRIP to Japan being complete without a visiting an onsen. But admittedly, disrobing in front of strangers to immerse yourself in hot springs can seem quite intimidating at first, especially in Japan, land of so many cultural strictures. While onsen at five-star hotels usually have a handy how-to guide, there are many unwritten rules when it comes this centuries-old bathing ritual.

What is onsen exactly?

What is onsen : Maru-no-yu, KAI Poroto
Maru-no-yu, the public hot springs at KAI Poroto. Courtesy of Hoshino Resorts

Onsen are natural hot-spring waters whose mineral content is believed to have healing powers. The mineral composition will vary by location, and an onsen bathing experience might include gradual submersion of the body into just one warm pool or a series of several at increasing temperatures. You might be in a public onsen spa or private ryokan (a traditional inn built around springs). In any case, it’s a meditative enterprise meant to restore body and mind.

“Onsen bathing is not only about keeping the body clean,” says Keiko Watanabe, spa and wellness manager at Hoshino Resorts, “but it also helps regulate the autonomic nervous system, promote peripheral blood circulation, improve health, and has many other benefits.”

Note that the word “onsen” might refer to the waters themselves—which by Japanese law must be 25ºC or hotter or contain a certain composition of 19 substances—the pool or the spa/place that houses them.

How did onsen become an integral part of Japan’s wellness culture?

What is onsen : Public Hotsprings at Aman Spa, Japan
Public hot springs at Aman Spa. Courtesy of Amanemu

The bathing ritual is said to have evolved from Buddhist cleansing practices. In the seventh century, health-boosting herbal baths had become popular among Japanese nobility, and it eventually trickled down to the masses.

The practice became an established community activity during the Edo period, according to Yuki Kiyono, head of wellness and spa (group director) at Aman: “It was said that samurai would use onsen to restore their health and heal from battle. As well as alleviating fatigue and pain, onsen bathing was believed to generally improve well-being.” 

In ancient times, it was also seen as a way to recover physical strength from arduous tasks such as farming and fishing, Watanabe adds.

Onsen became so embedded in Japanese culture that it has shaped the travel industry, with locals traversing the country to experience various ryokans built around mineral-rich baths. Today, there are about 3,000 hot-springs resorts in Japan, some featuring springs that have been flowing for more than 1,000 years.

How do you prepare for an onsen?

What is onsen : Hand bath, KAI Beppu
Hand bath, KAI Beppu. Courtesy of Hoshino Resorts

It starts before you get there. The first rule is to avoid big meals and alcohol, Watanabe says. “An average of 800 cc of water is lost during bathing, so you have to be hydrated beforehand.”

Once you’re inside, you have to disrobe completely (no bikinis or trunks allowed) and clean yourself. “Today, many people shower rather than use an oke (a traditional wooden Japanese bucket) to clean their body,” Kiyono says. Both are fine as long as you thoroughly cleanse yourself because you want to ensure that the pools remain as pristine as possible. Most establishments provide complimentary shampoo, conditioner and soap but bringing your own beauty essentials is accepted and seen as a way to personalize the experience. 

Then, avoid the rookie move of entering the water right away as one would do in a Jacuzzi. “You have to familiarize the body with the temperature by pouring 10 to 20 pails of hot-spring water over the body, an act called kakeyu” Watanabe says. “You must start from the place furthest away from the heart such as fingers or toes.” 

Likewise, you shouldn’t soak the entire body at once but gradually—first soaking the knees, hips, chest and finally letting the water reach your shoulders. Then, all that’s left to do is take a deep breath, clear the mind, and enjoy.

How do you use an onsen and what is the etiquette?

What is onsen : Outdoor Onse, Aman Kyoto
Rotenburo, an outdoor onsen at Aman Kyoto. Courtesy of Aman Kyoto

Needless to say, the onsen is not a place for drinking, chatting, light swimming or, God forbid, selfies. Enjoyment entails quiet, mindful immersion. While soaking, make sure you keep your hair and towel out of the water; it’s considered bad etiquette if you let them touch it as they’re perceived as dirty.

How long does it take to reap the benefits of the mineral-rich waters? There’s actually no time requirement to staying in. Much like a Finnish sauna, it’s up to you to judge when you feel it’s the right time to surface (if you have sweat on your brow, it’s probably time). 

In fact, you can leave the water and reenter as many times as you want. If there are pools with different temperatures including a rotenburo, an outdoor bath that’s typically the hottest, the rule of thumb is to go to the one with the lowest temperature then progress to the highest, and back to the lowest before you finish.     

Once you’ve had your fill, you must shower again in case the hot-spring water is acidic, alkaline, or contains sulfur or iron. “When water with such qualities is left on the skin, it can lead to skin problems or it can affect the body,” Watanabe warns. 

What is onsen : Pavillion Bathroom at Aman Kyoto
Pavillion bathroom at Aman Kyoto, Japan. Courtesy of Aman Kyoto

Then you must dry yourself as it’s frowned upon to enter the changing room dripping wet. An older establishment would typically provide a tenugui—a small, woven cotton cloth—but nowadays you can find bigger towels, too. 

As you get dressed, don’t forget to moisturize (you’ll find lotions for free) as well as hydrate with the water provided. Once you’re dressed and refreshed, it’s time to indulge in your drink of choice, which you can get from the vending machines within the halls. The Japanese often go for cold teas or juices, with some opting for wholesome milk.

Where should I go for an onsen retreat?

This is no easy question considering there are thousands of hot-springs resorts in Japan, but both of these brands have several options alone.

What is onsen : Sora Suite Bathroom, Amanemu, Japan
Sora Suite bathroom, Amanemu. Courtesy of Amanemu

Amanemu. Forested in Honshu’s Mie Prefecture and overlooking Ago Bay, this is one of three Aman resorts in Japan, and it draws on the thermal waters of the surrounding Ise Shima National Park to offer both public and private onsen experiences.

Hoshino Resorts. This Japanese hotel conglomerate’s most famous brand is Hoshinoya, and you’ll find onsen at these luxury properties (including the one in Taiwan) and even a” sky onsen” at Hoshinoya Tokyo. They also have a hospitality brand dedicated to onsen travel called Kai, with 19 hotels built in classic hot-springs regions around Japan like Hakone, Nikko, Beppu, Hokkaido and more.

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