Introduction to Japanese Hot Springs

Hot springs are numerous in Japan, and for centuries the Japanese people have enjoyed hot spring bathing. Visits to hot spring resorts were hailed not only as a means of relaxation but also for the beneficial properties attributed to thermal spring water. Hot springs are still major attractions for vacationing Japanese, and many have been modernized and developed into large-scale resort complexes. Under the 1948 Hot Spring Law, the Japanese government recognizes as onsen only those hot springs that reach certain standards regarding temperature and mineral composition; the number of these as of 1990 was about 2300. Since 1954 the Ministry of Health and Welfare has accorded special recognition to 64 hot spring resorts capable of providing medical treatment.

A hot spring is defined by the Hot Spring Law as "hot water, mineral water, water vapor and other gases (except natural gas containing hydrocarbons as the main element) that issue from the ground with a temperature in excess of 25 degrees C (77 degrees F) or contain more than a predescribed amount of designated substances." Thus a cool mineral spring under 25 degrees C but containing more than a prescribed amount of the designated substances may be called a hot spring; even volcanic gas or volcanic vapor may be called a hot spring, creating cases that do not agree with the general concept of hot spring water.

The Japanese take special pleasure in mineral and hot spring bathing. The popularity of hot springs for such purposes in ancient Japan is described in the regional chronicles called fudoki. The Izumo fudoki reports that Tamatsukuri onsen was continually thronged with visitors and that by "bathing once, the visitor was made fair of face and figure; bathing twice, all diseases were healed; its effectiveness has been obvious since of old."

Dogo onsen in Iyo province (now Ehima prefecture) is reputedly the oldest hot spring in Japan. It was the site, according to tradition, of therapeutic bathing by several legendary or early historic emperors. Buddhist monks developed hot springs for medicinal purposes and used hot springs for the bathing that is part of the Buddhist purification ritual. Farmers and fishermen engaged in ritualistic baths at various times of the year.

Goto Konzan, a doctor in Edo (now Tokyo), noticed the effectiveness of hot spring bathing as a cure for certain disorders and in 1709 initiated the first medical study of hot springs, advocating the use of baths as therapy for various ailments. In 1874 the Japanese government undertook the chemical analysis of mineral springs. After the founding of the Balneotherapy Institute (now called the Medical Institute of Bioregulation) at Beppu onsen in Oita prefecture by Kyushu University in 1931, the medical study of hot springs began to be systematized, with many universities establishing research facilities at various hot springs. After World War II, national hot spring hospitals were created, making hot springs for medical treatment available around the country. Hot springs are utilized in the treatment of chronic rheumatism; neuralgia; chronic diseases of the stomach; intestines; liver, and gallbladder; hypertension; hemi-plegia; glucosuria; and gout. They are also used for treating external injuries and for postoperative treatment and rehabilitation.

Although hot springs are used mainly for bathing, in some places the heat they release is utilized for heating rooms and hothouses, for cooking food, for brewing sake, or for making miso (bean paste). In addition, certain hot springs that reach very high temperatures are now being utilized as energy sources for geothermal electricity generation. The first geothermal generation of electricity in Japan was carried out in 1925 in Beppu, producing 1 kilowatt. During the 1950s and 1960s more power was produced, and, spurred by the oil crisis of 1973, 50 megawatt power stations were constructed during the 1970s. As of 1990, 12 geothermal power stations were operating in Japan, altogether producing a total of 269950 kilowatts. Despite a national program to promote it, however, geothermal electricity generation remains relatively small in scale, limited by concern for the environment and turism.