Stinging nettles. View of the leaves of the stinging nettle (Urtica dioica). These plants are notorious for their stinging ability, which causes localised pain and swelling on the skin wherever contact is made. This is due to the presence of very fine hairs on the surface of the leaves and stems. When touched, these inject a mixture of ethanoic acid and biologically active chemicals such as histamine and serotonin. Nettles are also used medicinally. Chemicals in the roots act as a diuretic, and may also prevent benign prostatic hyperplasia (excessive growth of the prostate gland). Beating the body with nettles is said to ease rheumatic pains. Nettles are found worldwide.