What Causes Allergies?
Seasonal allergies, or "allergic rhinitis," are triggered by allergens -- substances that trigger reactions in the body. Pollens or molds are among the most common allergens, according to the American Academy of Allergy, Asthma and Immunology (AAAAI).
Pollen is produced by trees, grasses, and weeds, and is easily carried by the wind. The most common pollen allergens during the spring are trees such as oak, elm, birch, ash, hickory, poplar, sycamore, maple, cypress, walnut, and western red cedar; and grasses such as timothy, Bermuda, orchard, red top, and sweet vernal. In late summer and fall, weeds such as ragweed, sagebrush, pigweed, Russian thistle, and cocklebur become problematic for allergy sufferers.
People experience symptoms because they have a sensitivity to certain allergens. The allergens, usually inhaled, combine with an antibody called immunoglobulin E (IgE). IgE, the "allergic antibody," is normally present in your body at very low levels. But when you develop allergies, it's produced in larger quantities. When the allergen and IgE pair up, chemicals are released that cause inflammation. The resulting symptoms include itchy, watery eyes, sneezing, nasal congestion, a runny nose, drowsiness, and headaches.