Allergic Reaction

10 Common Allergy Triggers Slideshow Pictures Pets and Allergies Slideshow Pictures Home Allergy Quiz Slideshow Pictures

Medical Author:

John P. Cunha, DO, FACOEP

John P. Cunha, DO, FACOEP

John P. Cunha, DO, is a U.S. board-certified Emergency Medicine Physician. Dr. Cunha's educational background includes a BS in Biology from Rutgers, the State University of New Jersey, and a DO from the Kansas City University of Medicine and Biosciences in Kansas City, MO. He completed residency training in Emergency Medicine at Newark Beth Israel Medical Center in Newark, New Jersey.

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Medical Editor:

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, Chief Medical Editor

Melissa Conrad Stöppler, MD, is a U.S. board-certified Anatomic Pathologist with subspecialty training in the fields of Experimental and Molecular Pathology. Dr. Stöppler's educational background includes a BA with Highest Distinction from the University of Virginia and an MD from the University of North Carolina. She completed residency training in Anatomic Pathology at Georgetown University followed by subspecialty fellowship training in molecular diagnostics and experimental pathology.

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• Allergic Reaction Overview
• Allergic Reaction Causes
• Allergic Reaction Symptoms and Signs
• When to Seek Medical Care
• Allergic Reaction Diagnosis
• Allergic Reaction Treatment
• Self-Care at Home
• Medical Treatment
• Allergic Reaction Medications
• Other Therapy
• Follow-up
• Allergic Reaction Prevention
• Allergic Reaction Prognosis
• For More Information
• Web Links
• Synonyms and Keywords
• Authors and Editors
• Pictures of Common Allergy Triggers - Slideshow
• Pictures of Pets and Allergies - Slideshow
• Pictures of Home Allegy - Slideshow
• Read more on Allergic Reaction from Healthwise
• Viewer Comments: Allergic Reaction - Treatment
• Viewer Comments: Allergic Reaction - Symptoms

Allergic Reaction Overview

An allergic reaction is the body's way of responding to an "invader." When the body senses a foreign substance, called an antigen, the immune system is triggered. The immune system normally protects the body from harmful agents such as bacteria and toxins. Its overreaction to a harmless substance (an allergen) is called a hypersensitivity reaction, or an allergic reaction.

• Anything can be an allergen. Dust, pollen, plants, medications, (such as ibuprofen, sulfa drugs like sulfamethoxazole and trimethoprim [Bactrim], codeine, amoxicillin [Amoxil, Amoxil Pediatric Drops, Moxatag, Trimox]), foods (common food allergies include shrimp and other shellfish, peanuts), insect bites (such as from mosquitos 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).



• A reaction may include one or several symptoms.

Most allergic reactions are minor, such as a rash from poison ivy, mosquito or other bug bites, or sneezing from hay fever. The type of reaction depends on the person's immune system response, which is sometimes unpredictable.

In rare cases, an allergic reaction can be life-threatening (known as anaphylaxis). Each year in the United States, it is estimated that there are 150,000 cases of anaphylaxis. Up to 500-1,000 fatalities due to anaphylaxis occur each year.

Allergies are very common. The Asthma and Allergy Foundation (AAFA) states allergies affect 50 million Americans, is the fifth leading chronic disease in the U.S., and the third leading among children. More than 40 million people have indoor/outdoor allergies as their primary allergy. More than 17 million people visit their doctor for allergies annually, and food allergies account for 50,000 visits to the emergency room annually.