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February 3, 2012
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Allergic Reaction

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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.

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Allergic Reaction - Treatment

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Allergic Reaction

Antibiotics Introduction

Antibiotics are among the most frequently prescribed medications in modern medicine. Antibiotics cure disease by killing or injuring bacteria. The first antibiotic was penicillin, discovered accidentally from a mold culture. Today, over 100 different antibiotics are available to cure minor, as well as life-threatening infections.

Although antibiotics are useful in a wide variety of infections, it is important to realize that antibiotics only treat bacterial infections. Antibiotics are useless against viral infections (for example, the common cold) and fungal infections (such as ringworm). Your doctor can best determine if an antibiotic is right for your condition.

Types of Antibiotics

Although there are well over 100 antibiotics, the majority come from only a few types of drugs. These are the main classes of antibiotics.

  • Penicillins such as penicillin and amoxicillin
  • Cephal...

Read the Antibiotics article »


Read What Your Physician is Reading on Medscape

Hypersensitivity Reactions, Immediate »

The immune system is an integral part of human protection against disease, but the normally protective immune mechanisms can sometimes cause detrimental reactions in the host.

Read More on Medscape Reference »

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