When you hear the word "Onsen," what comes to mind? A steaming open-air bath, a secluded hot spring surrounded by snow-covered mountains, or perhaps a stroll through an onsen town in a yukata? Many foreign travelers visiting Japan look forward to experiencing an onsen as a highlight of their trip.

But what exactly is an "onsen"? How does it differ from a regular bath? As someone who has visited numerous onsens across Japan, I've learned the depth of onsen culture. This article provides a comprehensive explanation, from the definition of onsen to its culture and ways to enjoy it.

Definition of Onsen: Legally Defined

In Japan, onsens are clearly defined by the "Onsen Law." An onsen is "hot water, mineral water, and steam or other gases (excluding natural gas with hydrocarbons as the main component) that meet any of the following conditions" that emerge from the ground.

Condition 1: Temperature of 25°C or higher. The water temperature must be 25°C or higher at the time it emerges from the ground.

Condition 2: Contains a certain amount of specific components. It must contain at least one of the specified 19 components, such as lithium ions, hydrogen ions, iodide ions, or iron ions, in a prescribed amount.

Therefore, it doesn't necessarily have to be "hot." There are onsens at 25°C (called cold mineral springs). Conversely, if it contains specific components, it can be recognized as an "onsen" even if the temperature is low.

Every onsen facility displays an "onsen analysis certificate." This is an official document that lists the components, temperature, pH value, etc., of the onsen. Be sure to check it when you visit an onsen facility. I always check the onsen analysis certificate. Knowing the spring quality can greatly enrich your onsen experience.

Why Japan is a Hot Spring Superpower

The Japanese archipelago is located on the Ring of Fire. This geological feature makes Japan one of the world's leading hot spring superpowers.

There are over 27,000 hot spring sources, about 3,000 hot spring areas, approximately 18,000 hot spring facilities, and about 130 million annual users.

Every prefecture in Japan, from Hokkaido to Okinawa, has hot springs. This is extremely rare worldwide.

Japanese onsens are not only abundant in quantity but also in quality. All 10 types of spring qualities exist, offering a variety of benefits.

Differences Between Onsen and Regular Baths

Onsen is natural groundwater that emerges from deep underground. It's not tap water heated like a regular bath.

Onsen water contains various mineral components. These components create the unique benefits of onsen.

Many onsens naturally emerge at an optimal temperature (38-42°C). New onsen water continuously flows.

Depending on the spring quality, onsens have various colors, scents, and textures. Milky white, green, brown. The scent of sulfur. Silky texture. These are characteristics unique to natural onsens. I was moved by the unique scent and color when I first entered a milky sulfur spring.

What is "Gensen Kakenagashi"?

"Gensen Kakenagashi" is a method where freshly emerged onsen water is continuously poured into the bath, and the overflow is drained.

New onsen water is always added, with minimal water addition or heating, and it is not recirculated, making it clean. You can fully experience the original benefits of the onsen.

The circulation system filters and sterilizes used onsen water for reuse. While excellent in terms of hygiene, the onsen components are diluted.

Onsen facilities display labels like "Gensen Kakenagashi" or "100% Onsen." The "onsen usage status" is also listed in the onsen analysis certificate.

I prefer visiting onsens with Gensen Kakenagashi. The fresh quality of the onsen water is distinctly different from the circulation system.

Differences Between Onsen and Sento

Onsen uses natural hot springs and contains components defined by the Onsen Law. Most are located in the suburbs or tourist areas, with an entrance fee of about 500-2,000 yen.

Sento is a public bath using heated tap water, serving as a community-based public bathhouse. Located in residential areas of urban centers, the entrance fee is about 450-500 yen (in Tokyo).

However, some sento have natural hot springs, known as "onsen sento." These are hidden spots to enjoy onsen in urban areas.

History of Japanese Onsen

The history of Japanese onsen is very old. Japan's oldest historical texts, "Kojiki" and "Nihon Shoki," already mention onsens. Dogo Onsen has a history of about 3,000 years, and Arima Onsen about 1,300 years.

During the Heian period (794-1185), onsens were already used as places for healing. The culture of "toji," where nobles visited onsen areas to cure illnesses, began.

In the Edo period (1603-1868), onsen culture spread to the common people. Onsen rankings (a culture of ranking onsens like sumo rankings), toji trips (staying at onsen areas for weeks during the agricultural off-season), and the development of onsen towns (gathering of restaurants and inns).

Since the Meiji period (1868-), onsens have developed not only as medical facilities but also as places for tourism and leisure. The development of onsen medicine, improved access from urban areas due to railway development, and the development of onsen inns.

Today, onsens are deeply rooted in Japanese life. They are also very popular with foreign tourists and have become a must-experience in Japan travel.

Benefits of Onsen

Onsen has many scientifically proven health benefits. It promotes blood circulation, relieves fatigue, reduces stress, alleviates pain, improves skin, and boosts immunity.

The benefits vary depending on the spring quality. Simple onsens are effective for fatigue recovery, chloride springs for improving cold sensitivity, bicarbonate springs for skin beauty, and sulfur springs for skin diseases.

I also feel the health benefits of onsen. Regularly bathing in onsen helps maintain both physical and mental health.

How to Enjoy Onsen

Open-Air Bath

An outdoor onsen where you can bathe while feeling nature. Enjoy the scenery of each season.

Private Bath

A small onsen that can be used privately. Recommended for families or couples.

Strolling in Onsen Town

Stroll through the onsen town in a yukata. Enjoy visiting souvenir shops and restaurants.

Toji

A traditional style of long-term stay for onsen therapy. It allows you to reset both body and mind.

Onsen Ryokan

Experience Japanese culture deeply with in-room dining, kaiseki cuisine, and hospitality.

Onsen Etiquette

Wash your body before bathing, don't put towels in the bath, tie up your hair, bathe quietly, and don't bathe after drinking alcohol. These are basic manners.

Onsen is a public place shared with others. By following manners, everyone can enjoy onsen comfortably.

Conclusion: Onsen is Japan's Treasure

Onsen is a treasure created by Japan's nature. Natural groundwater, abundant mineral components, various spring qualities, long history, and health benefits. All these make onsen special.

I've visited onsens across Japan, and their splendor never fades no matter how many times I experience them. Each time, there's new discovery and excitement.

When you visit Japan, be sure to experience onsen. Onsen is one of the best ways to understand Japanese culture. Once you know the wonders of onsen, you'll likely become captivated by them.