The immune system is your body's defense system. It helps protect you from illness and infection. The immune system usually reacts to and attacks bacteria, viruses, and cancer cells. An allergy is when your body's immune system reacts to something harmless, such as food, plants, or medicine.
What is an allergic reaction?
What causes an allergic reaction?
Doctors aren't sure why some people who are exposed to a substance become allergic to it and others don't.
Common substances that trigger allergic reactions include:
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House dust
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Animal dander
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Pollen (of trees, grass, weeds)
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Molds
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Certain foods
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Certain medicines
What are the symptoms of an allergic reaction?
Mild allergic reactions may cause:
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Watery, itchy eyes
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Runny nose and sneezing
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Itchy skin, sometimes with a rash (hives)
Severe allergic reactions (anaphylaxis) may cause:
How do doctors tell if I have an allergic reaction?
How do doctors treat an allergic reaction?
How can I prevent allergic reactions?
The most important ways to prevent allergic reactions:
Avoiding an allergen may involve:
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Stopping a medicine
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Keeping pets out of the house or limiting them to certain rooms
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Using high-efficiency particulate air (HEPA) vacuums and filters
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Not eating a certain food
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Removing or replacing items that collect dust, such as soft furniture, carpets, and knickknacks
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Putting special covers on mattresses and pillows to keep out dust mites
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Using synthetic-fiber pillows
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Frequently washing bed sheets, pillowcases, and blankets in hot water
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Frequently cleaning the house, including dusting, vacuuming, and wet-mopping
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Using air conditioners and dehumidifiers in basements and other damp rooms
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Getting rid of cockroaches
With allergy shots, the doctor gives you shots of the substance you're allergic to. At first the shots have only a very, very tiny amount of the substance. The amount is too small to cause a severe reaction. Then the doctor gives you shots that have more and more of the substance. That way, your body can become used to the substance and not react to it. Allergy shots don't always work. And when they do work, you may have to keep getting the shots.
