The genus Parietaria has about 10 species, which are highly cross-reactive to each other. Parietaria pollen allergens (officinalis, judaica, lusitanica, creatica) are one of the most common causes of pollinosis in areas where the plants grow. A close correlation exists between the species P. judaica and P. officinalis. In some geographical areas one species may dominate, and IgE antibodies to only one of the species can be found in sensitised individuals.