Allergy may be induced by the fertilizing element of flowering plants produced by the male sexual organ. Pollens are fine, powdery, yellowish grains or spores, and sometimes remain in masses. Airborne pollen types are considered to be the major component of allergens. Pollen cause widespread upper respiratory tract and naso-bronchial allergy with manifestations like seasonal rhinitis, hay fever, and various types of bronchial troubles.
Pollen grains of grasses and conifers are considered to be the principal group of allergen producers in the world. In Bangladesh the incidence of allergen pollen is comparitively high than neighbouring countries. An experiment conducted by M.K. Pasha, Chittagong University revealed that in Bangladesh the major allergenic pollen grains are released by plants are: Lantana camara, Acacia species, Cassia fistula, Cocos nucifera, Eleusine indica, Datura metel, Amaranthus spinosus, Cynodon dactylon, Achyranthes aspera, Albizzia lebbeck, Brassica campestris, Cannabis sativa, Carica papaya, Mangifera indica, and Xanthium.