Coumarins are lactones that have had an intramolecular reaction where a lactone has fused to a benzene (aromatic) ring. Okay, that's the chemical explanation. Three groups of coumarins found in plants are furanocoumarins, hydroxycoumarins, and pyranocoumarins. What we're briefly touching on here is what coumarins do, where they're found, and what the warnings for them are.
Coumarins tend to be antiallergenic, anti-asthmatic, anticarcinogenic, anti-diabetic, anti-inflammatory, antimicrobial, antioxidant, antispasmodic, antiviral, calming, fungicidal, and hypotensive. They tone blood vessels and can relieve varicose veins and hemorrhoids.
Within herbs, certain plant families have significant coumarins including the Carrot Family, the Coffee Family, the Grass Family, the Pea Family, and the Rue Family. The aroma you smell after cutting grass or hay comes from the coumarins in the plants. In essential oils we find two furanocoumarins - Bergapten and Bergamotine. These are found in citrus oils that have been obtained by cold pressing and in Angelica Root, Bergamot, Rue, Mandarin Leaf, and Taget.
The warnings with coumarins mainly concern the furanocoumarins in essential oils because they are phototoxic. If you apply these oils topically at too high of a dilution rate (rates vary by oil) and are exposed to UV rays within 12 - 18 hours, the furanocoumarins can cause skin damage that ranges from temporary rash and discoloration to severe and permanent burn damage and discoloration. Take note that distilled Lime and Sweet Orange essential oils do not contain furanocoumarins and are not phototoxic.
There is one other factor to keep in mind with coumarins in herbs. By themselves, they have little to no anticoagulant ability; however, if the herb gets moldy, the coumarins in the plant are changed into a chemical called dicoumarol. Dicoumarol is anticoagulant and its effects cannot be reversed. As scientists studied this chemical, they decided to try to synthesize it. Eventually, they came up with something that was initially used as rat poison -- Warfarin®. Yes, you're reading that right - what started out as rat poison turned into a blood-thinning medication for humans. I explain this because, if you are taking Warfarin®, you need to have your INR monitored regularly if you ingest herbs that have coumarins as they may have the potential to interfere with it.
You can learn more about individual coumarins when their datasheets become available in the membership section.
The information contained in this blog is for educational purposes only and has not been evaluated by the Food and Drug Administration.