Causes

The immune system produces antibodies that defend against foreign substances. This is good when a foreign substance is harmful, such as certain bacteria or viruses. But some people's immune systems overreact to substances that don't normally cause an allergic reaction.

Allergy symptoms aren't usually life-threatening, but a severe allergic reaction can lead to anaphylaxis. Even if you or your child has had only a mild anaphylactic reaction in the past, there's a risk of more severe anaphylaxis after another exposure to the allergy-causing substance.

The most common anaphylaxis triggers in children are food allergies, such as to peanuts and tree nuts, fish, shellfish, wheat, soy, sesame and milk. Besides allergy to peanuts, nuts, fish, sesame and shellfish, anaphylaxis triggers in adults include:

• Certain medications, including antibiotics, aspirin and other pain relievers available without a prescription, and the intravenous (IV) contrast used in some imaging tests
• Stings from bees, yellow jackets, wasps, hornets and fire ants
• Latex

Although not common, some people develop anaphylaxis from aerobic exercise, such as jogging, or even less intense physical activity, such as walking. Eating certain foods before exercise or exercising when the weather is hot, cold or humid also have been linked to anaphylaxis in some people. Talk with your health care provider about precautions to take when exercising.

If you don't know what triggers an allergy attack, certain tests can help identify the allergen. In some cases, the cause of anaphylaxis is not identified (idiopathic anaphylaxis).