Cross-reactivity with Tagetes in Arnica contact eczema.

A 69-year-old patient, with known mercury and adhesive plaster allergy, developed facial dermatitis within 24 h of contact with arnica (Arnica). Skin testing showed positive reactions to arnica and, among various other plants of the Compositae, also to Tagetes sp. hybr. (marigold). Cross-reactivity between Tagetes and arnica has not previously been described.