Any of a class of glycosides, found widely in plants, that have detergent properties and form a lather when shaken with water. They are especially concentrated in the soapwort (Saponaria officinalis), whose foliage was formerly boiled and used as a soap substitute. Chemically saponins consist of a sugar group (e.g. glucose) linked to a steroid or triterpene group (a sapogenin). Their presence in plants is thought to act as a deterrent to herbivores—they are bitter-tasting and cause gastric irritation if ingested. They are also highly toxic to fish. If injected into the bloodstream they disrupt red cells, through their effects on plasma membranes. Some saponins are extracted commercially from plants such as yuccas and quillaja and may have beneficial effects on health.