Allergic rhinitis, often called hay fever, occurs when your immune system overreacts to particles in the air that you breathe-you are allergic to them. Your immune system attacks the particles in your body, causing symptoms such as sneezing and a runny nose. The particles are called allergens, which simply means they can cause an allergic reaction.

See a picture of how an allergen affects the body.

Several types of allergens cause allergic rhinitis, including pollens, mold, dust mites, animal dander, and cockroaches. Although polluted air is not an allergen, it can irritate your nose and lungs. An irritated nose or lungs may make an allergic reaction more likely when you breathe in an allergen.