Allergies are an abnormal response of the immune system. People who have allergies have an immune system that reacts to a usually harmless substance in the environment. This substance (pollen, mold, and animal dander, for example) is called an allergen.
Allergies are a very common problem, affecting at least 2 out of every 10 Americans.
- Itchy, watery eyes
- Itchy, runny nose
- Feeling tired or ill
- Hives (a rash with raised red patches)
The most severe allergic reaction is called anaphylaxis. In anaphylaxis, allergens cause a whole-body allergic reaction that can include:
- Hives and itching all over (not just in the exposed area)
- Wheezing or shortness of breath
- Hoarseness or tightness in the throat
- Tingling in the hands, feet, lips, or scalp