Allergic Reaction

• Allergic Reaction Overview
• Allergic Reaction Causes
• Allergic Reaction Symptoms
• When to Seek Medical Care
• Exams and Tests
• Allergic Reaction Treatment
• Self-Care at Home
• Medical Treatment
• Medications
• Other Therapy
• Next Steps
• Follow-up
• Prevention
• Outlook
• For More Information
• Web Links
• Synonyms and Keywords
• Authors and Editors
• Related allergies articles:
  Allergies - on WebMD
  Allergies - on MedicineNet

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, or allergic, reaction.

• Anything can be an allergen. Common dust, pollen, plants, medications, certain foods, insect venoms, viruses, or bacteria are examples of allergens.

• Reactions may be in one spot, such as a small skin rash or itchy eyes, or all over, as in a whole body rash.

• A reaction may include one or several symptoms.

In rare cases, an allergic reaction can be life threatening (see Anaphylaxis). Each year in the United States, over 400 people die from allergic reactions to penicillin, and over 50 people die from allergic reactions to bee and fire ant stings.

Most allergic reactions are much less serious, such as a rash from poison ivy or sneezing from hay fever. The reaction depends on the person but is sometimes unpredictable.

Allergies are very common.

Next: Allergic Reaction Causes »

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Last Editorial Review: 9/2/2005