An allergy is the most serious of the three conditions. It occurs when the body mistakes a food ingredient as harmful and defends itself by producing high levels of a type of antibody called immunoglobulin E. Sometimes a food allergy is life-threatening and requires immediate medical attention. The most common food allergies are to shellfish, nuts, fish, and eggs. A person with a food allergy may have symptoms similar to an intolerance or sensitivity, but he or she also can experience hives, throat swelling, and shortness of breath.
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