What are allergies Symptoms Allergies vs. An allergy is an overreaction by the body to the presence of substances called allergens.
Common allergens are pollens, household dust, molds, domestic animal dander, smoke, and some foods.
The immune system responds to these allergens by releasing histamine and other inflammation-causing chemicals in an attempt to rid the body of the allergens. The release of histamine produces the familiar symptoms of watery eyes, runny nose, and sneezing. Some people respond to allergies in other ways such as asthma, swelling of the face and neck, itching and skin rashes. Rarely, nausea, vomiting or diarrhea may be allergic reactions to food. Fever, sore throat and muscle aches are characteristic of URI's.