Allergic eczematous contact dermatitis caused by ragweeds (Ambrosia), named "ragweed oleoresin contact dermatitis," was found to be due to ten sesquiterpene lactones possessing a methylenegroup attached to the lactone. An additional 14 lactones possessing such a group and derived from ragweeds, are probably allergenic.
Mitchell JC, Roy AK, Dupuis G, Towers GHN. Allergic Contact Dermatitis From Ragweeds (Ambrosia Species)The Role of Sesquiterpene Lactones. Arch Dermatol. 1971;104(1):73-76. doi:10.1001/archderm.1971.04000190075012