Although the allergen in hay fever is usually plant pollen, allergic rhinitis can have other causes. These can be things like feathers, dust, or animal dander. Sometimes it is hard to know whether a stuffy nose or itchy eyes are due to pollen or another cause. People with allergies have developed antibodies through exposure to substances known as allergens. These antibodies circulate in the blood stream and localize in the tissues of the nose and in the skin.
Antibodies react with allergens, such as pollen or house dust.
When this happens, histamine is released in the blood. This causes the lining of the nose, sinuses, eyelids, and eyes to swell and is known as allergic rhinitis. These allergic attacks may last 15 to 20 minutes, or for several days. People with hay fever may get these symptoms every year when certain plants bloom. For many, hay fever is only a minor problem, for others it interferes with daily activities.