I was recently delighted to hear from an editor who works for Martha Stewart Living. She was writing an article on using the herb calendula as a topical treatment.
Not having any celestial source of knowledge, I did my usual thing and dug into all the published peer reviewed articles that I could find on the topic. I found the herb quite interesting, and am inspired to write an article of my own. Here are some of the tidbits that I learned and shared with this editor:
Botany and Culinary:
Botany and Culinary:
Calendula is related to marigold, and sometimes called “pot marigold”, but the marigold that most people plant in their gardens is not calendula. It is related to it; in the same family (Asteraceae, also called Compositae) but not the same genus (the genus of the marigold is Tagetes and that of calendula is Calendula).
Calendula grows very easily and has bright yellow or orange daisy-like flowers. (I once had some completely invade my garden here in Utah, it took me a day to pull them all out of my garden.)
Calendula flower petals are edible, sometimes tossed in salads for color.
Laying chickens are sometimes fed calendula flower petals along with their feed, which turns the yolks a brighter yellow from the carotenoid pigments in the flowers.
Some researchers are investigating the use of calendula extracts to kill snails that carry parasites in developing countries.
Safety: Although calendula seems generally pretty safe, there is insufficient information to recommend taking large amounts of it orally on a regular basis. A few petals here and there in salads on occasion, for example, is unlikely to hurt you. Pregnant or lactating women should avoid consuming it therapeutically simply because it is an unknown. It is in a family of plants that always raises a red flag for allergies. People with allergies to other plants in this family (ragweed, daisies, dandelion, sunflower, chrysanthemums, arnica, and other daisy-shaped flowers) are more likely to have an allergy to calendula, or to eventually develop one. People in this category should perform a patch test if they want to try calendula topically, and should avoid eating it.
Nonetheless, reports of allergies to calendula are uncommon in the scientific literature, compared to allergies of other asteraceae plants. There is one published report, from Russia, of a woman who gargled with a preparation of calendula and she suffered anaphylaxis, a severe allergic reaction:
Klin Med (Mosk). 1974 Apr;52(4):142-3.
Title: [Anaphylactic shock after gargling with an infusion of Calendula]
[Article in Russian]
Another study showed that after 433 patients were patch tested for calendula allergy, 9 responded positively, showing they had the potential for a bad reaction to calendula:
Contact Dermatitis. 2001 Nov;45(5):269-72.
Title: The seamy side of natural medicines: contact sensitization to arnica (Arnica montana L.) and marigold (Calendula officinalis L.).
Reider N, Komericki P, Hausen BM, Fritsch P, Aberer W.
Department of Dermatology and Venereology, University of Innsbruck, Austria.
Animal tests show calendula is relatively nontoxic. Cell and animal studies show nothing alarming, but more studies should be done. Because studies are incomplete, a 2001 report prudently says “it is concluded that the available data are insufficient to support the safety of these ingredients in cosmetic formulations.” (This is not surprising since it is the status of all but the most thoroughly studied herbs.) At that time is was judged to be used in around 200 different cosmetic products.
Title:Final report on the safety assessment of Calendula officinalis extract and Calendula officinalis.
Int J Toxicol. 2001;20 Suppl 2:13-20. Review.
Homeopathic calendula: Homeopathic preparations of calendula (not to be confused with naturopathic or holistic) involve a particular method of diluting the herb down to nonexistence in the preparation. Homeopaths believe the preparation retains a “memory” of what was once it, which is really rather bizarre when you think about it. This has never been proven by any experiment, though people have repeatedly tried to prove it. There is no evidence that homeopathic remedies in general work any better than a placebo, although they have been repeatedly tested. (They can work by the placebo effect, which sometimes is impressive however.) Nonetheless, for this reason, I would never use or recommend a homeopathic preparation—I would prefer one that has actual calendula in it.
Formulation: Most of the folkloric and scientific use of calendula involves the use of the outer ray flowers. Each flower has many tiny “disk” flowers, as well, in the center of the flower, but these are not usually used, nor is the green part of the herb. Curiously, we now know that the ray flowers have the highest percentage of faradiol (farrah DIE-all) esters, which are thought to be antiinflammatory, and that could explain how they help skin to heal. (The faradiol esters were 10 percent higher in ray flowers than disk flowers, and 100 percent higher than the green bits.)
Zitterl-Eglseer K, Reznicek G, Jurenitsch J, Novak J, Zitterl W, Franz C.
Title: Morphogenetic variability of faradiol monoesters in marigold Calendula officinalis L.
Phytochem Anal. 2001 May-Jun;12(3):199-201.
Also, the faradiol esters are oil-soluble, and not water or alcohol soluble. So the best method of obtaining them is to soak the outer flowers in something oily like vegetable oil, or petroleum jelly.
Faradiol esters are also found in sunflower petals, arnica petals, coltsfoot flowers, and dandelion herb. Arnica, however, often causes a rash, and the other plants are less well known.
The oil-based preparations will end up being colored, since carotenoid pigments that are colored are oil-soluble and will leach out from the flower petals into the oil. Carotenoids in moderate doses are known to be antioxidant and protective. (Megadoses of oral carotenoids may be harmful, though. Most megadoses of antioxidants end up being more harmful than helpful, unfortunately. I can talk about why that is, if you like, on your radio show...)
Water or alcohol preparations are less likely to contain the above faradiol esters and carotenoids, but more likely to contain common plant flavonoids, which are not unique to calendula but found in most plants. Flavonoids often act as protective antioxidants by a variety of different mechanisms, and may in theory have anti-cancer activity.
Faradiol esters’ activity: Faradiol esters in an a category of common plant molecules known as triterpenes (try-TERP-enes). Faradiol esters are “antiedemic” (relieve localized swelling of tissues) and antiinflammatory in a small number of animal studies. It is possible that other triterpenes in calendula have similar, but perhaps less potent, activities. Antiinflammatories in general relieve “heat, pain, redness and swelling”—the four common signs of acute (short term) inflammation. They can also speed healing. Inflammation is caused by the immune system over-reacting and causing damage. It is a case of friendly fire. Inflammation also commonly underlies, and we now think, perpetuates many disease processes. So it often helps to shut it off.
This study singled out the faradiol esters as the most active antiinflammatory agents in calendula flowers:
Planta Med. 1994 Dec;60(6):516-20. Title: The role of triterpenoids in the topical anti-inflammatory activity of Calendula officinalis flowers.
Della Loggia R, Tubaro A, Sosa S, Becker H, Saar S, Isaac O.
Istituto di Farmacologia e Farmacognosia, Universita di Trieste, Italy.
In the following study the faradiol esters from calendula were found effective in reducing the swelling of mouse ears that were treated with an irritant. A compound derived from calendula’s faradiol esters, called faradiol, was just as effective as indomethacin, a prescription antiinflammatory medicine which is similar to ibuprofen. J Ethnopharmacol. 1997 Jul;57(2):139-44.
Title: Anti-oedematous activities of the main triterpendiol esters of marigold (Calendula officinalis L.).
Zitterl-Eglseer K, Sosa S, Jurenitsch J, Schubert-Zsilavecz M, Della Loggia R, Tubaro A, Bertoldi M, Franz C.
Institute for Botany and Food Science, University of Veterinary Medicine Vienna, Wien, Austria.
Freeze-dried calendula extracts protected mice from the inflammatory effects of injections of carageenan and prostaglandin E1 in another study. White blood cells normally infiltrate the site of injection, causing swelling, but calendula prevented this from happening.
Vet Med Nauki. 1981;18(6):87-94.
Title: [Anti-inflammatory action of a group of plant extracts]
[Article in Bulgarian]
Shipochliev T, Dimitrov A, Aleksandrova E.
Another Bulgarian study showed that calendula extracts sped wound healing in rats:
Acta Physiol Pharmacol Bulg. 1982;8(4):63-7. Title: Influence of the physiological regeneration and epithelialization using fractions isolated from Calendula officinalis.
Klouchek-Popova E, Popov A, Pavlova N, Krusteva S.
Inflammation caused by an irritating chemical placed on mouse ears was relieved markedly by calendula extracts:
Phytochemistry. 1996 Dec;43(6):1255-60.
Title: Triterpene alcohols from the flowers of compositae and their anti-inflammatory effects.
Akihisa T, Yasukawa K, Oinuma H, Kasahara Y, Yamanouchi S, Takido M, Kumaki K, Tamura T.College of Science and Technology, Nihon University, Tokyo, Japan.
How does it work? This is always what I am most interested in, because some mechanisms are better than others, some are safer than others. So far, we don’t really know calendula works, because those studies have not been done.
But there is a hint that water and alcoholic extracts of calendula do not work like aspirin and other related (NSAID) drugs. These drugs prevent an enzyme (cyclooxygenase or “COX”) from making prostaglandins, and some prostaglandins are known to promote inflammation. Calendula and a number of other herbs were tested for this aspirin like-activity (tested for COX inhibition). Calendula was not singled out in the article for COX inhibition as other herbs were, so it doesn’t seem to work that way. However this study used alcohol and water extracts and these extracts do not contain the faradiol esters, so they don’t say anything about how the faradiol esters might work. It might still be that faradiol esters act like aspirin (but their structure is not very aspirin-like so I personally doubt that.)
Roum Arch Microbiol Immunol. 2003 Jan-Jun;62(1-2):117-29.
Title: Hydroalcoholic plant extracts with anti-inflammatory activity.
Herold A, Cremer L, Calugaru A, Tamas V, Ionescu F, Manea S, Szegli G.
National Institute of Research-Developmentfor Microbiology and Immunology Cantacuzino, Bucharest, Romania.
Looking at the structure of faradiol esters, they look very steroid-y to me, that is, they look like steroids. Steriods can be either hormonal, or inflammatory, in general. Some steroids have activities both of hormones and anti-inflammatories. We don’t know if calendula has any hormonal activity, those studies have not been done.
One of the most well-known steroidal antiinflammatories is hydrocortisone cream, or cortisol. In theory, faradiol esters might act like hydrocortisone, because they resemble hydrocortisone, but that is not known, the studies have not been done. Hydrocortisone and other antiinflammatory steroids work by preventing the precursor to prostaglandins (called arachidonic acid) from getting released from cell membranes. Aspirin-like drugs, on the other hand, prevent this arachidonic acid from being turned into prostaglandins by the enzyme cyclooxygenase (“COX”).
Clinical studies with actual people: These are always so much nicer, for so many reasons, than animal studies. There is only one well-designed one. This is a French study comparing oil-based calendula extracts to trolamine, published in the Journal of Clinical Oncology.
The punchline is that women using calendula (126 women) had statistically significantly less acute dermatitis than those using (128 women) trolamine (trade name Biafine). The dermatitis that radiation therapy causes is similar to sunburn, but can be more severe, with red skin, peeling, and blisters forming. The women using calendula also had less pain and this effect was also statistically significant. What I thought exciting about the study was that the women using calendula were more likely to continue radiation therapy without interruption, which is more likely to get rid of their cancer. Patients in the trolamine group requested 12 total suspensions of radiotherapy treatments because of dermatitis, but only 1 patient in the calendula group requested an interruption in her therapy, and that request was not related to her dermatitis.
J Clin Oncol. 2004 Apr 15;22(8):1447-53.
Title: Phase III randomized trial of Calendula officinalis compared with trolamine for the prevention of acute dermatitis during irradiation for breast cancer.
Pommier P, Gomez F, Sunyach MP, D'Hombres A, Carrie C, Montbarbon X.
Department of Radiation Oncology, Centre Leon Berard, 28 rue Laennec, 69373 Lyon Cedex 08, France.
You can read the article yourself if you want, if you link to https://www.jco.org/cgi/reprint/22/8/1447
The authors of the study are up front, which is nice, about a couple of limitations of their study. First, they did not compare calendula to an inactive placebo, which would be more ideal so we could see just how effective calendula is. But it perhaps it would have not been kind to give half of the women an ineffective skin treatment after their breasts were burned with radiation. Trolamine is often used on skin after it has been treated with lasers or radiation therapy. It actually is not thought to be all that effective, so in that respect it may have acted somewhat like a placebo.
Another limitation of their study was that it was single blind, not double blind. Ideally, you want neither the subjects nor the scientists to see who is getting what, so no one can subjectively form any preconceived bias for a particular treatment. But the calendula ointment is yellow, so it was impossible to disguise it from the patients. So they knew what treatment they were getting. The doctors, on the other hand, did not know who got what treatment, since the patients could were required apply their ointments many hours before their skin was examined by the doctors, and by that time their skin was not yellow.
The article mentions several times, by the way, that 30% of the women using calendula did not like applying it, (compared to 5% of the women using trolamine.) The article didn’t say why. Perhaps they did not like putting something so yellow on their skin, or perhaps the tactile sensation of the ointment was unpleasant. Trolamine did not have such a problem with compliance.
Rare and previously undiscovered carotenoids in calendula flowers: Carotenoids are a type of plant pigment that is common in plants; they are often yellow, orange, or red. They are likely anti-oxidant and free radical scavenging (that’s a good thing.) I was intrigued that three new versions of lycopene were discovered in orange, but not yellow, calendula flowers. The common form of lycopene, that we are most familiar with, is what makes tomatoes red. (These new versions have similar structure as chain-like molecules, but are “cis-trans isomers”, that is, they bend in different ways along the chain at locations of double bonds.) Orange calendula flowers also contain some carotenoids that are relatively rare in nature. We don’t know what their properties are, if any, but it is likely that they are at least similar in activity to other more common carotenoids:
Biosci Biotechnol Biochem. 2005 Nov;69(11):2122-8.
Title:Analysis of carotenoid composition in petals of calendula (Calendula officinalis L.).
Kishimoto S, Maoka T, Sumitomo K, Ohmiya A.
National Institute of Floricultural Science, Ibaraki, Japan. email@example.com