Allergenic nature of Parthenium hysterophorus.

Parthenin has been reported as the active allergen in Parthenium hysterophorus contact sensitivity. A study was carried out to test various chemical fractions of the plant for isolating and identifying the exact allergens. Two additional sesquiterpene lactones apart from parthenin have been shown to be allergenically active. Structures of these sesquiterpenoids are presented. Photopatch tests do not indicate a photosensitizing capacity for these compounds.