"Allergic rhinitis occurs when allergens in the air are breathed by a patient that is allergic to them, irritating and inflaming the nasal passages. Allergens may include dust mites, pollen, molds, or pet dander. In people who are allergic to them, these particles trigger the release of a chemical in the body that causes nasal congestion, sneezing, watery eyes, and runny nose. These symptoms can lead to poor sleep, which can result in significant daytime sleepiness and fatigue.
Allergic rhinitis (allergies) may occur year-round or seasonally. When it occurs seasonally it is usually caused by airborne particles from trees, grass, ragweed, or outdoor mold. Causes of year-round allergic rhinitis include indoor substances such as pet dander, indoor mold, cockroach and dust mites in bedding, mattresses, and carpeting."