Allergic Reaction Overview
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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.
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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