Arnica cream is a topical preparation that contains extracts of arnica, a perennial herb that can be poisonous to ingest but enjoys some popularity as a skin remedy, according to the American Cancer Society. As of 2015, there is limited scientific evidence to support the claims about arnica's healing properties.
Proponents of arnica suggest that topical use of the herb can assist in healing irritation, inflammation, wounds and bacterial infections, but these claims require more investigation, advises the American Cancer Society. Clinical studies have divided patients into groups where some receive arnica treatment and others receive a placebo for the purpose of testing the effectiveness of arnica in treating conditions such as pain, bruising and swelling. In some cases, there were reports of lower pain levels in the arnica group, but in many cases, researchers found no difference in the results.
Some individuals are allergic to arnica, which is a member of the plant family Asteraceae. Additionally, the effects of arnica on pregnant or breast-feeding women are unknown. These groups of people should avoid using arnica. Otherwise, arnica cream that contains small doses of the herb is generally safe for occasional use on the skin. However, high concentrations or frequent use of arnica can cause skin reactions. It's also not advisable to use arnica on broken skin or mucous membranes, as this can trigger severe reactions. Similarly, internal use of arnica can be dangerous and may rarely lead to death, warns the American Cancer Society.