XVI International Botanical Congess
A very small portion of atmospheric pollen will reach a compatible flower, and very few will also be deposited in the upper airways of mammals including man. Yet, some pollen types are causing health problems (pollinosis or 'hay fever'), because of the allergic sensitizing properties of certain substances called allergens. World-wide, the best known allergenic pollen types are Poaceae, Ambrosia, and Betula. Although symptoms of pollinosis are mainly localized in the eyes, nose, and throat, affliction of the lower airways (bronchial tubes) are also often observed. Pollen-allergenic activity carried by particles much smaller than intact pollen grains are thought to be responsible for this thoracic localization of symptoms.