An allergy is a condition in which the body’s immune system responds to a foreign substance, usually a protein.
Allergic reactions can be limited to mild skin rashes and itching, or they can be life-threatening. One kind of life-threatening allergic reaction, called anaphylactic shock, occurs when an individual is subjected to a foreign substance to which his or her body has already become sensitized—that is, a substance to which the individual has been exposed and has developed antibodies against.
