Allergic Reaction

General or Other | Allergy & Immunology | Allergic Reaction (Disease)


An allergic reaction is the hypersensitive response of the immune system of an allergic individual to a substance. Allergic reactions occur as a reaction of a persons immune system to normally harmless substances in the environment.

Symptoms and signs of an allergic reaction include any, some, or many of the following: skin: irritation, redness, itching, swelling, blistering, weeping, crusting, rash, eruptions, or hives (itchy bumps or welts); lungs: wheezing, tightness, cough, or shortness of breath; head: swelling or bumps on the face and neck, eyelids, lips, tongue, or throat, hoarseness of voice, headache; nose: stuffy nose, runny nose, sneezing; eyes: red, itchy, swollen, or watery or swelling of the area around the face and eyes; stomach: pain, nausea, vomiting, diarrhea, or bloody diarrhea; other: fatigue, sore throat.

Causes and Risk factors

A substance that causes a reaction is called an allergen. Anything can be an allergen: dust, pollen, plants, medications such as ibuprofen, sulfa drugs like sulfamethoxazole and trimethoprim, codeine, amoxicillin, foods (common food allergies include shrimp and other shellfish, peanuts), insect bites such as from mosquitoes or bees, animal dander, viruses, or bacteria are examples of allergens.

Reactions may occur in one spot, such as a small localized skin rash, itchy eyes, face bumps, or all over, as in a whole body rash such as or hives (urticaria).

Diagnosis and Treatment

For typical allergic reactions, a doctor will examine the patient and ask questions about the symptoms and their timing. Blood tests and X-rays are needed in case of unusual circumstances.

Treatments for allergies include avoiding known allergens, use of medications such as anti-histamines that specifically prevent allergic reactions, steroids that modify the immune system in general, and medications such as decongestants that reduce the symptoms. ...