Pollen and molds are the two main types of seasonal allergens. The type of pollen in the air depends on the growing season and the area of the country. Molds may be present year-round, especially in damp spaces of buildings and in furniture, such as mattresses and pillows. You may be allergic to all molds or just to molds that are present during one particular season. When the pollen or molds come into contact with these tissues in an allergic person, cells in the tissues release a chemical called histamine.
Histamine causes the tissues to itch, swell, and produce more mucus or tears than is normal.
If you have asthma and you breathe into your lungs the substances you are allergic to, you may have symptoms of asthma. Hay fever is usually diagnosed from your medical history. If your symptoms occur just in certain seasons, your health care provider will suspect that you have hay fever. A check of your ears, nose, throat, and lungs may confirm the diagnosis. You may have tests for specific allergies.