Shobu-yu (the sweet flag bath)

May 5th is the Boy’s day, a Japanese national holiday to celebrate and wish boys’ healthy growth and happiness. Japanese take a bath called Shobu-yu on this day.


1.What is Shobu-yu?

Shobu-yu is a bath in which leaves of Shobu plant are soaked. Shobu is a type of iris or sweet flag in English.


Shobu are sold at every supermarket in early May.People buy Shobu and put the leaves in a bathtub of hot water at home on May 5th.


The Shobu plant has been thought to be a kind of herb for driving away evil spirits since the old days in Japan. Its leaves have a strong scent and they were used medicinally. In the hope to have good health and a long life, people started using the leaves in the bath.


This is a main reason why the traditional custom, taking the Shobu bath on Children’s day, has been handed down to this day in Japan.


2. Relationship with samurai

There are some other reasons. The shape of the very pointy leaves reminded people of the Samurai sword, so they wanted to place it at the entrance in order to get rid of the evil spirits coming into the house. 


The name “Shobu” has the same sound as the word ‘Shobu (尚武)’ which means martial/Samurai spirit. Another Japanese word which has the same sound as ‘Shobu’ is ‘勝負’, which means ‘contest/match/game/win-defeat’. 


Obviously, it is important for a Samurai family to win in a match, so parents used Shobu for the Boy’s Day decoration by wishing the healthy growth of a boy who would become a great Samurai.


3. Health benefits

Shobu-yu offers health benefits. The plant contains many essential oil ingredients, such as Asarone and eugenol. You can expect the effect to relieve neurosis and backache from them.


In addition, the plant has a unique aroma that helps you to relax.


4. Conclusion

Many public bathes offer the Shobu-yu bath on May 5.

It might be an interesting experience for visitors to soak in the Shobu yu.



(1) “Shobu-yu – The origin and health benefit of the Japanese sweet flag bath”


(2)” Shobu (菖蒲) / Iris” on