An allergy is a type of immune system reaction that occurs when the body’s immune system overreacts to a substance that is normally harmless, such as pollen, pet dander, or certain foods. When a person is exposed to an allergen, their immune system mistakenly identifies it as a harmful substance and releases chemicals, such as histamine, to fight it off. This immune system reaction can cause a range of symptoms, such as itching, redness, hives, runny nose, sneezing, watery eyes, and difficulty breathing.
Allergies can range in severity, from mild to severe. In severe cases, an allergic reaction can be life-threatening and cause anaphylaxis, a rapid and severe reaction that can cause difficulty breathing, low blood pressure, and unconsciousness.
Common types of allergies include hay fever (allergic rhinitis), food allergies, skin allergies, and insect sting allergies. Allergies can be diagnosed through a combination of medical history, physical examination, and allergy testing, such as skin prick tests or blood tests. Treatment for allergies can include avoiding the allergen, taking medications, such as antihistamines or corticosteroids, or receiving immunotherapy, also known as allergy shots.