In hot water: Types of Japanese onsen and their surprising health benefits

Jozankei is a beautiful onsen city in Hokkaido. Pic: newtap77/Shutterstock

RELAXING in the tranquil waters of a Japanese onsen (hot springs) is an experience no traveler should miss.

These hot springs are found throughout the country in remarkable locations, with many renowned for their natural beauty and therapeutic benefits. With this in mind, we plunge into one of Japan’s oldest traditions.

What is an onsen?

Pic: Hirohito Takada/Shutterstock

Onsen bathing has a long history and is enshrined in Japanese culture. Its roots can be traced back more than 1,000 years when it was used as a purification ritual in the ancient religion of Shinto.

Later, during the Edo period, it became popular with ordinary citizens who visited the hot springs as part of their seasonal “togi” to cleanse their minds and bodies and promote better health. Today, there are more than 26,000 onsens in Japan, and they are popular with locals and tourists alike.

To be an “official onsen“, the geothermally heated water must be above 25 degrees and contain a certain amount of naturally occurring chemicals. Beyond this, onsens vary considerably in shape, size, color and form.

But broadly speaking, they can be defined as rotenburo, which are open-air outdoor pools, indoor onsens that are usually attached to ryokans or hitou which are secluded hot springs.

While some onsens allow mixed (konyoku) bathing, others insist on segregated pools for men and women. Similarly, some allow bathers to wear swimsuits, whereas others are strictly au naturel only.

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The benefits of onsen

Onsens are categorized according to their mineral content which can vary depending on geological factors and location. For this reason, some are more acidic while others are more alkaline, and of course, there are pools that fall somewhere in between.

The warm, soothing onsen waters are believed to stimulate the metabolism and boost the regulatory function of the autonomic nervous system. But each type is also thought to offer bathers specific health benefits when nutrients and chemicals from the water are absorbed through the skin, inhaled or drunk.

Types of onsen

Pic: Hirohito Takada/Shutterstock

Iron (Ferruginous) springs
These distinct red-brown onsens are believed to increase the body’s own iron levels as well as relief aches and pains associated with poor circulation and arthritis.

One of the most impressive iron-rich hot springs can be found on the volcanic island of Shikine-jima. The modest rock pools of the Jinata Onsen are only meters from the sea and offer visitors a unique place to enjoy the rolling ocean.

Acidic springs
While the steamy waters of acidic onsens are capable of dissolving aluminium coins, they also offer a surprising number of therapeutic benefits. These springs can ease stiffness, muscular pain and various symptoms associated with gynaecological problems and chronic fatigue.

The pools, like those found at the onsen resort of Kusatsu, also have a natural antibacterial quality owing to the sulphur, aluminium sulphate and chloride in the water.

Sodium bicarbonate saline springs
The crystal clear, alkaline springs known locally as “Bihada no Yu” (beautiful skin waters) gently remove dirt and excess oils to give bathers soft, smooth, and radiant complexions.

The water itself has an unusual but pleasant silky feel because of its sodium bicarbonate and sodium chloride content. The pools can be enjoyed either indoors or outdoors and some places, like the onsen town of Ureshino, offer both.

Sulphur springs
The inviting, milky white waters contain hydrogen sulphide which is thought to expand blood vessels and alleviate hypertension.

While the potency of springs can vary, the open-air Manza Onsen is believed to be Japan’s most sulphuric. It is best enjoyed in the winter when it is surrounded by snow and can offer stunning views of a wintery mountain landscape.

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