Plant by Plant

Calendula: The Compounds in the Flower and What the Studies Found

Calendula is the orange-flowered plant also called pot marigold, Calendula officinalis, and it belongs to the daisy family, Asteraceae. According to a 2023 review by Shahane and colleagues, the flowers are the part used in skin preparations, both the alcohol-based ones and the oil-based ones.

What's in the flower

The orange color of the flowers comes from pigments called carotenoids, which the flowers carry in large amounts. In calendula those include lutein, beta carotene, lycopene, flavoxanthin and zeaxanthin. The flowers also carry flavonoids, quercetin among them, and a group of compounds called triterpenoids (Shahane et al., 2023).

The triterpenoids are the group researchers have traced to a specific effect. In 1994, Della Loggia and colleagues took a calendula flower extract, split it into separate fractions, and tested each fraction on the skin of lab animals to see which one calmed inflammation, the redness and swelling the body produces around irritated tissue. Each fraction that showed activity was split again and retested until the active compounds were isolated. That method is called bioassay-guided fractionation.

The triterpenoids came out as the most important anti-inflammatory compounds in the flower. One of them, faradiol monoester, mattered most because the extract contains so much of it. Faradiol on its own, without the ester attached, was the strongest compound they tested, and in their test it matched indomethacin, an anti-inflammatory drug. That free form of faradiol wasn't present in the extract itself, though, so inside the extract the monoester is the compound that accounts for most of the activity. They also found that the anti-inflammatory effect of different extracts rose in step with how much faradiol monoester each one contained (Della Loggia et al., 1994).

What the wound studies found

In 2019, Givol and colleagues searched five research databases for every study that compared calendula flower extract on its own against a control for wound healing. They found 14: seven animal experiments and seven clinical trials in people.

The fresh wound results lined up the most. Five animal studies and one randomized trial in people found that calendula-treated wounds moved through the inflammation stage faster and formed more granulation tissue, the new tissue that fills a wound in as it heals.

The chronic wound results were more varied. Two studies on venous ulcers, which are slow-healing sores on the lower leg, found the ulcers shrank more with calendula than in the control groups. A randomized trial on diabetic leg ulcers found no difference. Burn studies split the same way, with two animal studies showing a protective effect when calendula was given before the burn, and one human trial showing no difference from the control (Givol et al., 2019).

One trial in that set tested calendula on skin during radiation treatment. Pommier and colleagues assigned 254 people who'd had breast cancer surgery to apply either a calendula ointment or trolamine, the cream many hospitals already used, to the treated skin after every radiation session. Skin reactions of grade 2 or higher showed up in 41% of the calendula group and 63% of the trolamine group. The calendula group also reported less pain from the radiation, and rated their satisfaction higher, even though they found the ointment harder to apply (Pommier et al., 2004). Givol's review also includes a second radiation trial, which compared calendula with a water-based gel cream and found no difference.

Where that leaves calendula

The most consistent results so far come from fresh wounds, and every one of these studies tested calendula applied to the skin. Givol's team found some evidence of benefit, consistent with calendula's traditional use on wounds, and called for larger, well-designed trials as the next step. The chemistry gives those trials a clear compound to measure, since the 1994 work showed the anti-inflammatory effect rising with the amount of faradiol monoester in an extract.

Go further

My Mama & Baby guide has a full chapter on calendula as a skin flower, alongside colloidal oatmeal for dry, sensitive skin: kbaco.net/downloads/seasonal-mama-baby

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