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. Common dust, pollen, plants, medications, certain foods, insect venoms, animal dander, viruses, or bacteria are examples of allergens.
•Reactions may occur 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 (known as anaphylaxis). Each year in the United States, over 400 people die from anaphylactic reactions to penicillin, and nearly 100 Americans die from anaphylactic reactions to insects, according to the Asthma and Allergy Foundation of America (AAFA).
Most allergic reactions are much less serious, such as a rash from poison ivy or sneezing from hay fever. The type of reaction depends on the person but is sometimes unpredictable.
Allergies are very common. The AAFA states allergies account for more than 17 million visits to the doctor each year. More than half of all allergy visits are for seasonal allergies. More than 7 million people visit their doctor for skin allergies annually, and food allergies account for 30,000 visits to the emergency room.