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.

An allergic reaction occurs only in people who have a condition called atopy. It means that allergens are likely to cause an allergic reaction. An atopic person often develops more than one allergy. Experts don't know why people become atopic and have allergic reactions. Most people who have allergies have family members who also have some kind of allergy.

The first time you are exposed to an allergen in the air, your body's immune system may recognize the allergen as a foreign substance. Your body reacts by making antibodies against the allergen. The next time you are exposed to the allergen, the antibodies attack it, releasing histamine and other chemicals that cause the symptoms of your allergy. This is called sensitization. If sensitization occurs, it tends to be after age 3. Children who develop allergic rhinitis after age 3 generally become allergic to many allergens, including dust mites, dander on pets, and pollens.¹

See a picture of how an allergen affects the body.

If you have a pollen allergy, your symptoms may vary according to the climate and the types of plants that grow in your area. If you have symptoms in:

• Winter and spring, you are probably allergic to tree pollens.
• Summer, you are probably allergic to grass and weed pollens.
• Late summer and fall, you probably are allergic to ragweed or other weed pollens, such as tumbleweed or sage.

Complications

Allergic rhinitis can affect your health if you do not treat it. If it lasts a long time, you may have complications such as sinusitis, plugged ears and ear infections. Many people with asthma also have allergic rhinitis, and researchers are looking at whether allergic rhinitis may lead to asthma.

Allergic rhinitis can also affect your quality of life. You may avoid seeing people, have problems sleeping, and feel tired or irritable. You may have trouble with school or work.