An "allergy" is a sensitivity of your immune system to something that is ordinarily harmless. When your body tries to get rid of the "allergen" (foreign substance), you experience symptoms like sneezing, itchy, watery eyes, and a runny, stuffy nose. Typical allergens include pet dander, pollen, dust mites and mold.

The medical description for allergy symptoms is "allergic rhinitis." ("Rhinitis" comes from the ancient Greek word "rhinos" for nose, and "itis" means inflammation.)

"Seasonal allergic rhinitis" describes allergies that change with the seasons due to pollen from plants. For people with seasonal allergies, symptoms come and go with the pollination seasons of certain trees, grasses or weeds. Pollen levels from these plants can vary day to day, depending upon several factors, including the weather. High pollen levels can, in turn, affect the severity of symptoms.

"Perennial (or chronic) rhinitis" describes allergies that can occur any time of the year, which are caused by substances like dust mites, mold spores, cockroaches or pet dander. For more information on allergies, you can read our frequently asked Questions & Answers.