Demystify Japan’s Hot Water Baths: Onsen vs Sento

If you close your eyes and imagine a quintessential Japanese experience some will consider tucking into a bowl of ramen in a back alley, or enjoying an omakase sushi meal near the old Tsukiji Fish Market. Others picture the cherry blossoms drifting down in dramatic sakurafubuki (storm of falling petals) fashion, or geisha walking through the well-preserved districts of Kyoto.

For those of us fortunate enough to have soaked in the therapeutic waters of Japan’s numerous geothermal hot spots, onsen are at the forefront. Whether you’re staying at a traditional ryokan with a private rotenburo (open-air onsen bath), or just soaking your feet in a public ashiyu (foot bath), it’s hard to forget the calming and transportive effect.

There are various forms of hot water baths when you travel to Japan, and I’m here to demystify these for you. The main contenders you’re likely to run into while traveling are onsen and sento, though there are some unique variations like the aforementioned ashiyu which I’ve recently run into in Takayama, Hakodate, and Arashiyama. If you see one along your travels, be sure to pop off your shoes and take a moment to relax!

Sento

Sento are found throughout the country and are also often referred to as public baths. As many older Japanese homes didn't have their own baths, it was extremely common for each neighborhood to have a sento to service the local residents. While most contemporary Japanese homes have their own bathrooms complete with soaking tub, there are still some homes in older districts that depend on their local bathhouses. You pay a small fee to rent a towel, locker, and make your way into the bathing area to wash then soak in the larger baths.

Ashiyu Footbath in Gunma

difference between sento and onsen is the all in the water. Sento water is essentially tap water that is heated with a boiler for bathing. There are some really fun, almost theme park style, sento around Japan that are worth a visit if you want a unique cultural experience. Some "Super Sento" have numerous bathing options from individual wooden tubs to shallow stone baths where you lie on the ground in several inches of hot water. Saunas, creative therapy rooms like coal rooms, herbal rooms, ice rooms with a snow machine in the ceiling, and much more may be enjoyed as part of your admittance. Massages, snacks, and drinks are usually available for some additional cost.

Sento can be a laid back every day type of experience, or a luxurious retreat, depending on the location you choose to visit! Here are a few suggestions if you want to try a relaxing Japanese custom while in Tokyo:

- Saito Yu *tattoos are okay at this establishment

- Arai Yu

- Fukunoyu [Honkomagome]

Onsen

Due to Japan’s volcanic activity, there are thousands of onsen throughout the country. Global Base Camps tours often include onsen visits, usually in conjunction with a traditional ryokan stay. These can be noted as onsen, rotenburo, tenboburo, open-air baths, and hot springs. Onsen translates to "hot spring" but there is more to these healing waters than simply being geothermally heated.

Dogo Onsen, Matsuyama

order to be granted the title of "onsen", the bath must be filled directly by a local spring source and must have a minimum percentage of minerals, which are believed to have healing effects. The mineral composition varies based on location and types of onsen can be broken down into smaller sub-sects of water and mineral type like alkaline, acidic, simple, sulfur, etc.

These combinations of natural minerals such as sodium chloride, zinc, calcium, magnesium, sulfate, iron, and potassium in conjunction with the thermal waters are thought to penetrate into the body to help relieve joint and muscle pain as well as aid overall relaxation. Many studies about the health benefits of onsen attribute regular soaking to helping with everything from arthritis to maintaining beautiful skin. There is even a dedicated field of medicine for studying treatment of disease by bathing called balneology.

In addition to the above effects, the onsen waters are said to have special restorative benefits to combat oxidation, giving them a "fountain of youth" quality.

Onsen waters normally range from a minimum of about 35ºC/95ºF to upwards of  42ºC/107ºF. Some ryokan will offer several baths at different temperatures so you can work your way up to the hottest, or dip into a cold water bath between soaking sessions. If visiting in winter, however, I personally recommend laying in snow briefly between soaks to stimulate your body.

Onsen are a joy to soak in, even if some of their natural benefits are yet to be proven by science. If you need more of a reason to hop in the nearest tub, many ryokan and specialty onsen towns or resorts will add therapeutic or occasionally wacky ingredients to the onsen water for an extra kick. Hakone's Yunessun Onsen is well known for their wine (see vinotherapy for another layer of reputed benefits), coffee, and green tea baths.

Some locations add seasonal or special ingredients like royal jelly, whole yuzu (a type of citrus fruit), and seaweed. Baths with unique ingredients should have a sign noting the add-in, so you can learn about the benefits before you sink into the waters.

Another must-try that's a bit intimidating at first glance is a denkiburo, or "electric bath." These are more often found at sento, but are occasionally offered at onsen. You may see a posted sign with a warning for anyone with heart issues to avoid these tubs. The current in the bath can vary from mild to strong, and takes a bit of getting used to. An electrical current runs through the bath water and the pulses can aid muscle relaxation. If you're game to give the denkiburo a try, dip in a toe or your hand to gauge the strength of the current before stepping in.

A few onsen or onsen towns to consider on your next trip to Japan:

- Ooedo Onsen Monogatari - Tokyo

- Kusatsu Onsen - Gunma

- Kinosaki Onsen - Hyogo

- Gero Onsen - Gifu

- Noboribetsu Onsen - Hokkaido

- Dogo Onsen - Ehime

There is no bad season for soaking in Japan, but we do recommend the winter, or spring and autumn evenings which have lower temperatures to aid longer bathing comfort.

Post-Bath Rituals

The onsen experience in Japan, is about much more than just bathing. While the hot waters are relaxing, the atmosphere and time devoted to self-care are also very important. Many rotenburo allow you to take in the local scenery as you bathe. These views highlight natural beauty such as forests, mountains, coastlines, and rivers. Other baths are built in small gardens with landscaping meant to evoke peace and tranquility. These thoughtful surroundings can help you achieve a calmer almost meditative state, which helps to rejuvenate your mind as well as your body.

Once you've had enough time in the baths, a cool beverage is the perfect end to your onsen or sento visit. Many offer a variety of drinks, from cold milk to draft beer, that you can have while unwinding. Do be sure to rehydrate if you have spent a longer time soaking.

Onsen towns encourage travelers to wear yukata (cotton robes similar to kimono) and take a stroll in the cooler evening air. This is highly recommended for a memorable and romantic honeymoon or anniversary.

Since Japan is blessed with so much geothermal activity, there may be a convenient onsen experience to add to your next trip to Japan. Be sure to ask your travel specialist if you're interested in taking part in this stress reducing and peaceful aspect of Japanese life!