The chemical allantoin in the plant Symphytum officinale, more commonly known as comfrey, helps new skin cells grow, keeps skin cells healthy and decreases inflammation, as explained by the University of Maryland Medical Center (UMMC). People use comfrey to heal wounds and bruises, and reduce inflammation caused by sprains, strains and arthritis. Comfrey is generally safe when used topically. Historically, comfrey was a traditional remedy for gastrointestinal problems, but the substance can produce serious side effects when taken internally.
Liver Toxicity
Comfrey roots and leaves contain pyrrolizidine alkaloid chemicals that are toxic to the liver, according to the UMMC. These chemicals can cause severe and even life-threatening liver damage. Internal comfrey use is linked to liver cancer and to fatal hepatic veno-occlusive disease, in which small veins in the liver become blocked. In July 2001, the U.S. Food and Drug Administration banned all oral comfrey products. Canada, the United Kingdom, Germany and Australia also forbid the sale of oral products containing comfrey. People should be cautious about using comfrey topically as well, because it can be absorbed through the skin. No one should use comfrey on broken skin because the herb may enter the bloodstream.
Allergic Reaction
Rarely, some people may experience an allergic reaction to comfrey root. Signs as listed by the Physicians' Desktop Reference include difficulty breathing, tightness in the throat or chest, chest pain, hives, rash, itchy skin or swollen skin. An allergic reaction to comfrey root should be considered a medical emergency.
Pregnancy Considerations
Pregnant and breastfeeding women should not use comfrey because any amount can be toxic to the baby due to comfrey's effects on the liver. Additionally, comfrey has abortive effects, as noted by Drugs.com, and it can lead to miscarriage or premature labor.
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