By definition, allergies are the abnormal response of the immune system to substances that are usually harmless, such as pollen, fur or peanuts. When the immune system reacts, the result is the symptoms such as sneezing, itching and watery eyes.

Allergies are often associated with foods or seasonal changes. When weather warms up, trees, plants and grasses emit pollen into the air, which often triggers reactions in people. Some people have allergies that last year-round as well, with reactions to plants, animals, food and more.

There are several ways in which patients can be exposed to allergens. Perhaps the most common is inhalation or skin exposure, and this can occur with pollen, ragweed or animal dander. Symptoms include: