Knitback
Scientific Name: Comfrey
Other Names: Ass Ear, Black Root, Blackwort, Bruisewort, Common Comfrey, Consolidae Radix, Consound, Gum Plant, Healing Herb, Knitbone, Salsify, Slippery Root, Symphytum Radix, Symphytum officinale, Wallwort
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Uses
Comfrey contains chemicals that are unsafe to take by mouth. Some of these chemicals, known as pyrrolizidine alkaloids, have been associated with liver damage in humans. Some study animal that were given comfrey developed liver cancer.
In 2001, the U.S. Food and Drug Administration (FDA) and the U.S. Federal Trade Commission (FTC) asked manufacturers to remove all oral comfrey products from the U.S. market. Oral forms of comfrey are also prohibited in several other countries, but they may be sold in some places if they are labeled as a dietary supplement. Warnings were also placed on the labels of topical products that contain comfrey. As recently as December 2003, the Canadian health organization, Health Canada, re-issued warnings that comfrey products may contain harmful chemicals and that comfrey should neither be taken orally nor be applied to raw skin. Not all pyrrolizidine alkaloids are poisonous to humans, but the kinds, amounts, and proportions of pyrrolizidine alkaloids in comfrey products may vary greatly. Which type of comfrey plants were used, where they grew, what the weather conditions were, what time of year they were harvested, how they were processed, and where they were stored, all may affect the composition of commercial comfrey products. Similar products from different manufacturers and even different batches of the same product may have very different contents.
In addition, individual response to pyrrolizidine alkaloids is also quite variable. Some individuals, particularly children, senior adults, poorly nourished individuals, and those who have chronic illnesses, may have adverse results from doses of comfrey that are not toxic to other individuals. In a few documented case reports, however, young and middle-aged adults with no apparent health conditions are believed to have suffered liver damage from taking comfrey. The damage may be gradual, so comfrey poisoning may not be evident for periods up to 3 months.
Especially when high doses are used, or when low doses have been taken for long periods of time, pyrrolizidine alkaloids have been associated with causing a rare, but severe condition known as hepatic veno-occlusive disease. In this condition, the blood veins in the liver become clogged because a liver enzyme changes pyrrolizidine alkaloids into chemicals that may stick to the inside of veins and damage vein tissue. They may also damage lung tissue, potentially resulting in pulmonary hypertension, which is high blood pressure in the artery from the heart to the lungs. Some of the chemicals produced when pyrrolizidine alkaloids break down may stay in the body for years, continuing to damage blood vessels or other tissue.
However, comfrey contains several potentially beneficial substances that may be applied to the skin. Generally, it has high concentrations of:
Allantoin, a protein that encourages new cells to grow
Rosmarinic acid, which is anti-inflammatory
Tannins, that help to firm skin tone
Comfrey may also have topical pain-relieving effects. Because comfrey also contains mucilage, which swells in liquids, it forms a soft, sticky covering that stays in contact with the skin. All of these properties make comfrey useful when applied topically to soothe and treat arthritis pain, bruises, minor skin irritation, and sprains. It should be used only on small places of unbroken skin, however--not on large areas or open wounds. A mouth rinse made from comfrey may have some benefit in soothing sore gums and sore throat, but care must be taken not to swallow it. The mouth should be rinsed thoroughly with plain water after a comfrey rinse has been used.
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