What is it?
An essential oil distilled from the flower heads of mountain arnica, Arnica montana, a daisy-family plant of European mountains. The flowers hold only 0.2 to 0.35 percent essential oil, which is used mainly as a fragrance. Many products sold as “arnica oil” are instead arnica flowers steeped in a vegetable oil, a form of arnica extract. Arnica preparations have long been used in European folk medicine on bruises and sprains.
Key information
- Arnica flowers contain sesquiterpene lactones, mainly helenalin and its relatives, which are thought to cause a delayed allergic skin reaction known as arnica dermatitis.
- Swallowing arnica products has caused severe gastroenteritis, a rapid heartbeat, muscle weakness and death.
- In 2001 the CIR Expert Panel found the available data insufficient to support the safety of arnica extract and arnica in cosmetics.
- The European Medicines Agency does not recommend arnica preparations for children under 12 or during pregnancy or breastfeeding.
More information
Arnica’s distinctive compounds are sesquiterpene lactones, chiefly helenalin, dihydrohelenalin and their esters, which make up 0.3 to 1.0 percent of the dried flowers. The distilled flower oil is different: a 2025 analysis found it was mostly E-caryophyllene, caryophyllene oxide, germacrene D, farnesyl acetate and dodecanal, and did not report helenalin among its components.
Helenalin-type lactones are thought to cause arnica dermatitis, a delayed (type IV) allergy seen in people who handle the flowers or use arnica preparations. The European Medicines Agency’s herbal committee reviewed arnica in 2014 and found the safety of skin use of certain arnica preparations well documented in adults and adolescents. The most common side effects were allergic skin reactions such as itching, redness and eczema, which may occur in about 1 in 100 users. It said people allergic to daisy-family (Asteraceae) plants should not use arnica and, for lack of data, did not recommend it for children under 12 or during pregnancy and breastfeeding.
Swallowing arnica is dangerous. The Cosmetic Ingredient Review (CIR) Expert Panel noted that ingestion of arnica products has caused severe gastroenteritis, nervousness, a rapid heartbeat, muscle weakness and death, and Germany’s Commission E limited arnica to external use. In its 2001 review, the Panel concluded that the available data were insufficient to support the safety of arnica extract and arnica in cosmetics, asking among other things for genotoxicity tests in a mammalian system; one extract was mutagenic in a bacterial test.
Keep arnica products away from children and out of the mouth. If you know you are allergic to daisy-family plants, check labels for any Arnica Montana ingredient.
Sources: International Journal of Toxicology (2001): CIR final report on the safety assessment of Arnica montana extract and Arnica montana; European Medicines Agency: Assessment report on Arnica montana L., flos (2014); Molecules (2025): Effect of different Arnica montana plant parts on the essential oil composition, antimicrobial activity, and synergistic interactions with antibiotics
