An allergic reaction is an overreaction of the immune system to a substance called an allergen. Allergens include chemicals, foods, medicines, mold, plants, and pollen.
Symptoms of an allergic reaction can range from mild and annoying to severe and life threatening.
- Allergens can affect any tissue in the body, such as the airway, eyes, gastrointestinal tract, nose, lungs, and skin.
- Some allergic reactions, such as hives or itching around an insect bite or where a plant or chemical touched the skin, affect only one area of the body.
- Other allergic reactions may affect the entire body, causing itching, swelling, or difficulty breathing.
- A severe allergic reaction (called anaphylaxis) can lead to shock and even death. Allergic reactions do not occur the first time a person is exposed to an allergen. A person may become more sensitive to the allergen with each exposure.
