The plants possesses leafy, unbranched stems (often tinged with red). It grows in patches, attaining a height of 70 cm. The broad, lanceolate, sessile leaves are opposite and between 4 and 12 cm long. Its sweetly scented flowers are radially symmetrical and pink, or sometimes white. Each of the five flat petals have two small scales in the throat of the corolla. They are about 2.5 cm wide. They are arranged in dense, terminal clusters on the main stem and its branches. The long tubular calyx has five pointed red teeth.

As its common name implies, it can be used as a very gentle soap, usually in dilute solution. It has historically been used to clean delicate or unique textiles; it has been hypothesized that the plant was used to treat the Shroud of Turin. A lathery liquid that has the ability to dissolve fats or grease can be procured by boiling the leaves or roots in water. Take a large handful of leaves, bruise and chop them and boil for 30 minutes in 1 pint/600ml of water; strain off the liquid and use this as you would washing-up liquid. In the Romanian village of Sieu-Odorhei, natives call the plant “Sǎpunele”. It is traditionally used by the villagers as a soap replacement for dry skin.