Sensitization to arnica.
Allergens: Sesquiterpene lactones such as xanthalongine, helenalin, carabron and other substances of this group which have not yet been experimentally investigated must be regarded as potential contact allergens.
Sensitizing potency: Strong. Experimental sensitization showed a strong sensitizing potency both with the wild plants and with the commercial drug material as well as the individual isolated sesquiterpene lactones.
Frequency of sensitization: In comparison to other plants, arnica allergy occurs relatively frequently due to its versatile use. Arnica is one of the most important contact allergy inducing species within the composite family. Sensitization occurs not only in people who cultivate, harvest, extract and process the plants (occupationally), but above all in individuals who use arnica tinctures and other arnica-containing topicals.
Improper application (not diluted down) may initially lead to irritant dermatitis with blistering, which may subsequently lead to sensitization.
Cross-reactions with other composites, in particular tansy, yarrow, chrysanthemums, feverfew and sunflowers have been observed. Cross-reactions may also occur with other plant species (e.g. laurel and magnolia) which also contain sesquiterterpene lactones.