Almost all arnica sold is not an essential oil. It is a carrier oil the flowers have been steeped in, or a tincture, because distilling arnica gives a tiny and costly yield. That distinction matters, because helenalin and the other compounds arnica is researched for are too heavy to carry over into a distilled oil. A review of trials found arnica preparations beat placebo for bruising, swelling and pain after surgery and injury.^[1] Those trials used gels, creams and tinctures, not the essential oil.^[1]