Arnica (Arnica montana) has a long history of traditional use for treating minor injuries, including abrasions, bruises, and sprains. The plant has been used in European folk medicine for centuries, typically as a topical preparation (such as ointments, creams, or gels). The rationale behind arnica's use for abrasions is largely based on its believed anti-inflammatory and antimicrobial properties, as well as anecdotal reports of pain relief and promotion of wound healing. However, most traditional applications advise against using arnica on broken skin, including open abrasions, because arnica can be irritating and even toxic if absorbed through damaged skin in significant quantities.

Scientific evidence supporting arnica's efficacy specifically for abrasions is limited. Most clinical studies focus on its effects for bruising and muscle soreness rather than open wounds. The available scientific literature suggests that while arnica may help reduce inflammation and bruising under certain circumstances, it is not generally recommended for use on open abrasions due to the risk of allergic reactions and toxicity. Reputable sources, including the National Institutes of Health (NIH) and the European Medicines Agency (EMA), advise that arnica should not be applied to broken skin.

In summary, arnica's use for abrasions is justified primarily by traditional practices rather than robust scientific evidence, and modern medical guidance cautions against its application to open wounds.