arnica

Arnica is a genus of perennial plants in the sunflower family (Asteraceae). The best known species is Arnica montana, commonly called mountain arnica, native to Europe; other species include Arnica chamissonis in North America. They are leafy perennials with bushy growth and bright yellow flower heads; the flowers produce the medicinal material used in topical products.

Chemical constituents include helenalin and other sesquiterpene lactones, flavonoids, and essential oils. These compounds are associated with anti-inflammatory effects but also with skin irritation in some people. Because of their irritant potential, preparations contain restricted concentrations and are not intended for internal use.

Arnica is used in traditional herbal medicine topically for bruises, sprains, muscle soreness, and localized inflammation. Commercial products include ointments, creams, and gels, and arnica tinctures used by some practitioners. Homeopathic arnica preparations are highly diluted and used for similar indications, though evidence is limited.

Evidence and safety: Systematic reviews have found insufficient evidence that arnica is effective for preventing or treating bruising or reducing muscle soreness beyond placebo, and evidence for osteoarthritis is inconclusive. Topical arnica can cause contact dermatitis and skin irritation in susceptible individuals. Ingested arnica preparations can be toxic, with risks including nausea, vomiting, and more serious toxicity; internal use is not recommended by many health authorities. Arnica should not be applied to broken skin or mucous membranes, and use during pregnancy or lactation is typically cautioned.

Regulatory status: Arnica products are widely sold as herbal medicines and cosmetic ingredients, with regulation varying by jurisdiction. They are generally considered adjuncts rather than primary treatments for injury or pain.