Comfrey has been widely used in folk remedies as far back as the 16th century in different areas of Europe and Asia. It’s been highly acclaimed as a miracle drug and has been banned in several countries for being a health hazard. While there is no denying that comfrey can cause potentially lethal liver damage, it is also clear that when used properly, it can be helpful in many ways from moisturizing skin to quickly healing severe wounds. This makes comfrey a very puzzling plant that merits investigation. Just how dangerous can this plant be anyway?
In truth, the plant is extremely dangerous in many ways that one wouldn’t even imagine. Symphytum officinale (a common form of comfrey found in North America) has a more than slight resemblance to the highly lethal plant, foxglove. Foxglove [Digitalis purpurea] can be found throughout New England as well as a few Northwestern states. The most widely known case of mistaken foxglove ingestion took place in Washington when an elderly couple drank a home-made tea using foxglove instead of comfrey [1]. About an hour later, the wife suffered from nausea, vomiting, dizziness, and sweating. She died before being admitted into the hospital, while the husband died from a refractory ventricular fibrillation after being in a stable condition for 17 hours.
Mistaken foxglove use isn’t the only danger of comfrey. Comfrey is a known source of hepatotoxic pyrrolizidine alkaloids (PA’s), meaning it is a carcinogen that affects the liver. The danger is that small veins are destroyed which can lead to cirrhosis and eventual liver failure. Some scientists argue that America should follow the lead of Canada and Germany and have comfrey banned [2]. It is widely known that PA’s can cause both acute and chronic veno-occlusive disease (VOD) of the liver (This is when veins of the liver are destroyed), but there is little evidence in cases of human VOD that would point specifically to comfrey [3]. The few cases that have shown a link to comfrey poisoning were uncertain and the two cases that identified PA’s from herbal teas were only noted after ingestion of the tea. It would seem that if comfrey were to be banned, a considerable amount of testing and study should go into precisely what the dangers of the plant are, especially when one takes the benefits of comfrey in mind.
Comfrey is the primary source of allantoin, a chemical compound that has potent healing and soothing properties. It is a common folk remedy with minor fractures to heat a compress of comfrey leaves and place it over the break to speed up the healing process [4]. This technique was also used in World War I with serious wounds, due to the allantoin present. This is also the reason that wounds infested by maggots would heal faster, as the maggots secrete allantoin [5].
Allantoin has many medicinal uses, especially for skin diseases. It allows water to bind to the layer of skin that it is acting on, as well as directly acting on keratin molecules and improving their ability to hold more water, a trait that would be helpful for those suffering from psoriasis. The allantoins dissolve the cement holding cornified cells together in calluses, as well as provide a non-irritating skin moisturizer. Certain studies have also shown that allantoin may offset in vivo free radical activity. In vivo free radical activity is a result of outside sources acting on the body, as tobacco smoke, toxins, or pollutants, which can damage cells, proteins, and DNA by altering its chemical structure.
With all this in mind, it seems hard to believe that all these benefits come from the same plant that so many people denounce for its effect on the liver. The reason for this discrepancy is the form that the comfrey is taken in. As a tea, it is potentially dangerous, and is ingested as opposed to only being in contact with the skin. This is most likely due to the fact that the pyrrolizidine alkaloids only have an effect on the body if ingested. It is also true that the PA’s are not as toxic when they are in their original form [6]. The process of making tea from the leaves could very possibly change the form of the pyrrolizidine alkaloids found in comfrey.
Studies have shown that when applied to the skin, comfrey is anything but harmful. There is no reason that comfrey should not be used as long as it is not ingested. It has been shown to reduce pain sensitivity to UV-B irradiation as well as get rid of redness of the skin [5]. Allantoin has also proved to be a very efficient substitute to soap and water. In a test taking place at an elementary school, students using the allantoin-based product were 33% more likely to stay healthy throughout the course of the study than the group of students who used a placebo product [4]. It is also notable that the only cases where pyrrolizidine alkaloids in comfrey has been cited as the cause of the problem are cases where comfrey is used in a tea or cereal [2].
Comfrey has proven to be an effective answer to skin irritation of all kinds. That is too say a temporary irritation as opposed to an irritation caused by a disease such as psoriasis. Furthermore, studies on comfrey’s effects in relation to healing minor fractures and bruises should be conducted before any consideration goes into banning it whatsoever. The same goes for its effect on serious wounds. It seems that since allantoin is the chemical produced by maggots that comfrey may be helpful in the same manner.
As for the confusion between foxglove and comfrey, that is an evolutionary tactic that one must learn to overcome to use the comfrey, not unlike the Julia butterfly adapting in appearance to resemble the toxic Monarch butterfly. Some tell-tale signs of comfrey are that its leaves taper more at the apex and base, its smaller veins do not extend into the wings of the leaf-stalk, and the comfrey leaves have stiff isolated hairs on the surface of the leaves [7].
It should be warned against being used as a tea, because there is an obvious hazard on account of the pyrrolizidine alkaloids found in comfrey. But the potential beneficial properties of comfrey are too effective and helpful to not be looked into further. Studies should definitely be conducted in the near future so that comfrey can be an alternative source for an end to skin irritation and a speedy recovery from broken bones and severe injuries.

REFERENCES

[1]. Manteiga R, et al. ‘Risks Associated with Consumption of Herbal Teas.’ Reviews of Environmental Contamination & Toxicity 1997; vol.150, page 23.

[2]. Anonymous. ‘No Comfort in Comfrey.’ The Science Teacher May 2000; vol. 67, is. 5, page 14.

[3]. Zuckerman M, et al. ‘Hepatic Veno-Occlusive Disease as a Result of a Traditional Remedy: Confirmation of Toxic Pyrrolizidine Alkaloids as the Cause, Using an In Vitro Technique.’ Journal of Clinical Pathology Sept 2002; vol. 55, is. 9, pages 676-80.

[4]. Baumann L. ‘Cosmeceutical Critique: Allantoin.’ Skin & Allergy News June 2003; vol. 34 is. 6 page 10.

[5]. Bone K. ‘Topical Comfrey Helps Sprained Ankles.’ Townsend Letter for Doctors and Patients Jan 2001; page 140.

[6]. Dharmananda S. ‘Safety Issues Affecting Herbs: Pyrrolizidine Alkaloids.’ http://www.itmonline.org/arts/pas.htm Nov 2001.

[7]. Grieve M. ‘A Modern Herbal | Comfrey.’ http://botanical.com/botanical/mgmh/c/comfre92.html 1995.