See this chalky stuff building up around this onsen bath? Looks pretty gross, right?
Wrong.
This chalky looking residue is actually the hot spring's mineral deposits, known affectionally as 'yunohana'. Yu (湯) means hot water, onsen or bathing water, and hana (花) means flower in Japanese, giving these tiny mineral crystals their name.
Yunohana form around the spring when the spring source is particularly rich in mineral deposits.
The Japanese have been bathing in hot springs for thousands of years, and bathing in waters that are very rich in minerals has proven therapeutic uses, such as relieving stress, eliminating toxins, reactivating the metabolism, improving blood circulation, regenerating skin cells, or boosting the immune system.
As the yunohana mineral deposits are an indication of the water's high density of minerals, onsen baths with visible signs of natural yunohana are considered undisputedly exceptional quality by the Japanese.
The tiny yunohana crystals don't dissolve in the water, which can leave it with an incredible silky feel, not to mention a mesmerising shimmer, and can sometimes give the water an etherial milky hue.
Yunohana are so popular, in certain areas of Japan where the spring water is particularly rich in minerals, the deposits are cultivated and collected in hot water fields called yubatake (湯畑), to be gathered up and sold as unique bath salts.
There are over 3000 hot springs in Japan, and each spring's yunohana can give waters different qualities, in texture, and characteristics such as colour, scent and various health benefits, so yunohana can make great souvenirs of different onsen towns when visiting Japan.
Adding yunohana to your bath at home can instantly transform boring tap water into a magical onsen experience, one that helps you relax, boosts the immune system, and leaves the skin feeling incredibly silky and smooth.
For maximum effects from the beneficial yunohana rich water, don't rinse off after bathing, as leaving this natural residue on the skin will allow the minerals to work for longer.