Sauna, Onsen & the Global Culture of Heat Purification

Japan is in the midst of its "Third Sauna Boom." The first came in the 1960s with the introduction of Finnish saunas. The second arrived in the 1990s with the super-sento (mega bathhouse) wave. The third — and by far the largest — was ignited by the 2019 manga and TV drama "Sa-dō" (サ道) by Katsuki Tanaka, which introduced the concept of "totonou" to mainstream Japanese culture.

"Totonou" (ととのう) — literally "to be in order" — describes a state of mental and physical bliss achieved through the sauna-cold plunge-rest cycle. The word was nominated for Japan's Word of the Year in 2021. With 17.8 million enthusiasts and approximately 1 million new converts annually, sauna culture has become one of Japan's fastest-growing wellness movements.

Finland is synonymous with sauna — 3.3 million saunas for 5.5 million people. But the archaeological record tells a more complex story. Japan's mushiburo (蒸し風呂, steam bath) tradition appears in the 9th-century Makuranososhi: "Stones are placed inside small cottages. After heated, water is poured on them to produce steam." During the Kamakura period (1185-1333), cave-based steam baths proliferated across Japan.

The iwaburo (石風呂, stone bath) ruins near Kobe — from Toyotomi Hideyoshi's Yunoyama Goten — date back over 400 years. But heat-bathing in Japan likely goes back millennia further, intertwined with the volcanic landscape that gave birth to onsen culture. Whether Japan's heat traditions predate Finland's is debatable. What's undeniable is that both civilizations — separated by 8,000 km — independently arrived at the same insight: heat purifies the body and awakens the spirit.

Japan sits on the Pacific Ring of Fire. 27,000+ hot springs feed 3,000+ onsen facilities across the archipelago. Volcanic minerals — sulfur, sodium, iron, radium — each carry specific healing properties recognized by Japanese pharmacology for centuries. Where the sauna purifies through dry or wet heat, the onsen purifies through mineral dissolution: the earth's chemistry entering the body through the skin.

Modern Japanese wellness facilities increasingly combine both: sauna followed by onsen, or onsen followed by sauna, creating a complementary cycle of heat, mineral absorption, and cold contrast. The growing popularity of löyly (the Finnish steam ritual) in Japanese saunas represents a cultural cross-pollination that both countries would recognize — because the underlying wisdom is shared.