Tagetes minuta (Mexican marigold), a common weed in south eastern Africa and subtropical America has a vesicant primary irritant effect on intact skin and can cause severe and prolonged allergic contact dermatitis, with cross-sensitization to other Compositae plants. This is demonstrated with patch tests using fresh plants and with diluted extracts in three sensitive patients and in 43 controls. Tagetes minuta also has several other noxious effects on mammals and insects. Its action on human skin, including sensitization, is similar to that of the closely related genus Helenium.
Verhagen AR, Nyaga JM. Contact Dermatitis From Tagetes minutaA New Sensitizing Plant of the Compositae Family. Arch Dermatol. 1974;110(3):441-444. doi:10.1001/archderm.1974.01630090075019