As I was walking through the forest of the Institute for Nature Study in Meguro, Tokyo this autumn, I came across lots of these seeds on the ground … a fellow hiker told me that if you dropped the seeds into a pet bottle of water, you’d have a foamy soap solution. This is because the endocarps contain saponin so it was used as substitute for soap in olden days in Japan and apparently, by other cultures such as the Native Americans as well as in India where they are a popular ingredient in Ayurvedic shampoos and cleansers. They are used in Ayurvedic medicine as a treatment for eczema, psoriasis, and for removing freckles. Soap nuts have gentle insecticidal and antimicrobial properties and are traditionally also used for removing lice from the scalp. — A.K.
See original page Soapnut tree (mukuroji) for more details and photos on the soapnut tree.