In early spring, allergic rhinitis is caused by pollinating trees. During the late spring and early summer, allergic rhinitis is caused by pollinating grasses. In the late summer and early fall months, pollinating ragweed and other weeds are the culprit. Dust Mites and Mold . If your allergies last all year, you may be allergic to dust mites or mold.
Dust mites are present all year long and are found in large quantities in carpeting and bedding.
Molds are parasitic, microscopic fungi whose spores float in the air like pollen. Outdoor mold spores begin to appear after a spring thaw and also in the fall. Those allergic to pets are allergic not to the animal's hair, but to an airborne allergen found in the saliva, dander, or urine of an animal. There are various forms of nonallergic rhinitis, which produce year-round symptoms, especially nasal congestion.