They work like soap because their shells contain a substance called saponin, which is released when it comes in contact with warm water. The inner seed is hard and black and contains no saponin. Reetha/ Soap nuts can be used in whole or in powdered form. It is gentle on human hands. It removes dirt from clothing in a gentle, highly effective way. Because of its mildness, it preserves the colours and the structure of your valuable clothing longer than normal detergents. It's so gentle that is not even necessary to add a softener. The laundry turns out amazingly soft! Because of these characteristics, soapnuts are excellent detergents.