Comfrey (Symphytum officinale) is sometimes used on the skin to treat wounds and reduce inflammation from sprains and broken bones. Comfrey roots and leaves contain allantoin, a substance that helps new skin cells grow, along with other substances that reduce inflammation and keep skin healthy. Comfrey ointments have been used to heal bruises as well as pulled muscles and ligaments, fractures, sprains, strains, and osteoarthritis. In the past, comfrey was also used to treat stomach problems. However, it has toxic substances called pyrrolizidine alkaloids that damage the liver and can lead to death. Comfrey is no longer sold in the U.S., except in creams or ointments. The United Kingdom, Australia, Canada, and Germany also have banned the sale of oral products containing comfrey.